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diff --git a/Documentation/i2c/busses/i2c-ali1535.rst b/Documentation/i2c/busses/i2c-ali1535.rst new file mode 100644 index 0000000000..6941064730 --- /dev/null +++ b/Documentation/i2c/busses/i2c-ali1535.rst @@ -0,0 +1,45 @@ +========================= +Kernel driver i2c-ali1535 +========================= + +Supported adapters: + * Acer Labs, Inc. ALI 1535 (south bridge) + + Datasheet: Now under NDA + http://www.ali.com.tw/ + +Authors: + - Frodo Looijaard <frodol@dds.nl>, + - Philip Edelbrock <phil@netroedge.com>, + - Mark D. Studebaker <mdsxyz123@yahoo.com>, + - Dan Eaton <dan.eaton@rocketlogix.com>, + - Stephen Rousset<stephen.rousset@rocketlogix.com> + +Description +----------- + +This is the driver for the SMB Host controller on Acer Labs Inc. (ALI) +M1535 South Bridge. + +The M1535 is a South bridge for portable systems. It is very similar to the +M15x3 South bridges also produced by Acer Labs Inc. Some of the registers +within the part have moved and some have been redefined slightly. +Additionally, the sequencing of the SMBus transactions has been modified to +be more consistent with the sequencing recommended by the manufacturer and +observed through testing. These changes are reflected in this driver and +can be identified by comparing this driver to the i2c-ali15x3 driver. For +an overview of these chips see http://www.acerlabs.com + +The SMB controller is part of the M7101 device, which is an ACPI-compliant +Power Management Unit (PMU). + +The whole M7101 device has to be enabled for the SMB to work. You can't +just enable the SMB alone. The SMB and the ACPI have separate I/O spaces. +We make sure that the SMB is enabled. We leave the ACPI alone. + + +Features +-------- + +This driver controls the SMB Host only. This driver does not use +interrupts. diff --git a/Documentation/i2c/busses/i2c-ali1563.rst b/Documentation/i2c/busses/i2c-ali1563.rst new file mode 100644 index 0000000000..eec32c3ba9 --- /dev/null +++ b/Documentation/i2c/busses/i2c-ali1563.rst @@ -0,0 +1,30 @@ +========================= +Kernel driver i2c-ali1563 +========================= + +Supported adapters: + * Acer Labs, Inc. ALI 1563 (south bridge) + + Datasheet: Now under NDA + http://www.ali.com.tw/ + +Author: Patrick Mochel <mochel@digitalimplant.org> + +Description +----------- + +This is the driver for the SMB Host controller on Acer Labs Inc. (ALI) +M1563 South Bridge. + +For an overview of these chips see http://www.acerlabs.com + +The M1563 southbridge is deceptively similar to the M1533, with a few +notable exceptions. One of those happens to be the fact they upgraded the +i2c core to be SMBus 2.0 compliant, and happens to be almost identical to +the i2c controller found in the Intel 801 south bridges. + +Features +-------- + +This driver controls the SMB Host only. This driver does not use +interrupts. diff --git a/Documentation/i2c/busses/i2c-ali15x3.rst b/Documentation/i2c/busses/i2c-ali15x3.rst new file mode 100644 index 0000000000..d4c1a2a419 --- /dev/null +++ b/Documentation/i2c/busses/i2c-ali15x3.rst @@ -0,0 +1,122 @@ +========================= +Kernel driver i2c-ali15x3 +========================= + +Supported adapters: + * Acer Labs, Inc. ALI 1533 and 1543C (south bridge) + + Datasheet: Now under NDA + http://www.ali.com.tw/ + +Authors: + - Frodo Looijaard <frodol@dds.nl>, + - Philip Edelbrock <phil@netroedge.com>, + - Mark D. Studebaker <mdsxyz123@yahoo.com> + +Module Parameters +----------------- + +* force_addr: int + Initialize the base address of the i2c controller + + +Notes +----- + +The force_addr parameter is useful for boards that don't set the address in +the BIOS. Does not do a PCI force; the device must still be present in +lspci. Don't use this unless the driver complains that the base address is +not set. + +Example:: + + modprobe i2c-ali15x3 force_addr=0xe800 + +SMBus periodically hangs on ASUS P5A motherboards and can only be cleared +by a power cycle. Cause unknown (see Issues below). + + +Description +----------- + +This is the driver for the SMB Host controller on Acer Labs Inc. (ALI) +M1541 and M1543C South Bridges. + +The M1543C is a South bridge for desktop systems. + +The M1541 is a South bridge for portable systems. + +They are part of the following ALI chipsets: + + * "Aladdin Pro 2" includes the M1621 Slot 1 North bridge with AGP and + 100MHz CPU Front Side bus + * "Aladdin V" includes the M1541 Socket 7 North bridge with AGP and 100MHz + CPU Front Side bus + + Some Aladdin V motherboards: + - Asus P5A + - Atrend ATC-5220 + - BCM/GVC VP1541 + - Biostar M5ALA + - Gigabyte GA-5AX (Generally doesn't work because the BIOS doesn't + enable the 7101 device!) + - Iwill XA100 Plus + - Micronics C200 + - Microstar (MSI) MS-5169 + + * "Aladdin IV" includes the M1541 Socket 7 North bridge + with host bus up to 83.3 MHz. + +For an overview of these chips see http://www.acerlabs.com. At this time the +full data sheets on the web site are password protected, however if you +contact the ALI office in San Jose they may give you the password. + +The M1533/M1543C devices appear as FOUR separate devices on the PCI bus. An +output of lspci will show something similar to the following:: + + 00:02.0 USB Controller: Acer Laboratories Inc. M5237 (rev 03) + 00:03.0 Bridge: Acer Laboratories Inc. M7101 <= THIS IS THE ONE WE NEED + 00:07.0 ISA bridge: Acer Laboratories Inc. M1533 (rev c3) + 00:0f.0 IDE interface: Acer Laboratories Inc. M5229 (rev c1) + +.. important:: + + If you have a M1533 or M1543C on the board and you get + "ali15x3: Error: Can't detect ali15x3!" + then run lspci. + + If you see the 1533 and 5229 devices but NOT the 7101 device, + then you must enable ACPI, the PMU, SMB, or something similar + in the BIOS. + + The driver won't work if it can't find the M7101 device. + +The SMB controller is part of the M7101 device, which is an ACPI-compliant +Power Management Unit (PMU). + +The whole M7101 device has to be enabled for the SMB to work. You can't +just enable the SMB alone. The SMB and the ACPI have separate I/O spaces. +We make sure that the SMB is enabled. We leave the ACPI alone. + +Features +-------- + +This driver controls the SMB Host only. The SMB Slave +controller on the M15X3 is not enabled. This driver does not use +interrupts. + + +Issues +------ + +This driver requests the I/O space for only the SMB +registers. It doesn't use the ACPI region. + +On the ASUS P5A motherboard, there are several reports that +the SMBus will hang and this can only be resolved by +powering off the computer. It appears to be worse when the board +gets hot, for example under heavy CPU load, or in the summer. +There may be electrical problems on this board. +On the P5A, the W83781D sensor chip is on both the ISA and +SMBus. Therefore the SMBus hangs can generally be avoided +by accessing the W83781D on the ISA bus only. diff --git a/Documentation/i2c/busses/i2c-amd-mp2.rst b/Documentation/i2c/busses/i2c-amd-mp2.rst new file mode 100644 index 0000000000..ebc2fa8993 --- /dev/null +++ b/Documentation/i2c/busses/i2c-amd-mp2.rst @@ -0,0 +1,25 @@ +========================= +Kernel driver i2c-amd-mp2 +========================= + +Supported adapters: + * AMD MP2 PCIe interface + +Datasheet: not publicly available. + +Authors: + - Shyam Sundar S K <Shyam-sundar.S-k@amd.com> + - Nehal Shah <nehal-bakulchandra.shah@amd.com> + - Elie Morisse <syniurge@gmail.com> + +Description +----------- + +The MP2 is an ARM processor programmed as an I2C controller and communicating +with the x86 host through PCI. + +If you see something like this:: + + 03:00.7 MP2 I2C controller: Advanced Micro Devices, Inc. [AMD] Device 15e6 + +in your ``lspci -v``, then this driver is for your device. diff --git a/Documentation/i2c/busses/i2c-amd756.rst b/Documentation/i2c/busses/i2c-amd756.rst new file mode 100644 index 0000000000..bc93f392a4 --- /dev/null +++ b/Documentation/i2c/busses/i2c-amd756.rst @@ -0,0 +1,29 @@ +======================== +Kernel driver i2c-amd756 +======================== + +Supported adapters: + * AMD 756 + * AMD 766 + * AMD 768 + * AMD 8111 + + Datasheets: Publicly available on AMD website + + * nVidia nForce + + Datasheet: Unavailable + +Authors: + - Frodo Looijaard <frodol@dds.nl>, + - Philip Edelbrock <phil@netroedge.com> + +Description +----------- + +This driver supports the AMD 756, 766, 768 and 8111 Peripheral Bus +Controllers, and the nVidia nForce. + +Note that for the 8111, there are two SMBus adapters. The SMBus 1.0 adapter +is supported by this driver, and the SMBus 2.0 adapter is supported by the +i2c-amd8111 driver. diff --git a/Documentation/i2c/busses/i2c-amd8111.rst b/Documentation/i2c/busses/i2c-amd8111.rst new file mode 100644 index 0000000000..d08bf0a7f0 --- /dev/null +++ b/Documentation/i2c/busses/i2c-amd8111.rst @@ -0,0 +1,43 @@ +========================= +Kernel driver i2c-adm8111 +========================= + +Supported adapters: + * AMD-8111 SMBus 2.0 PCI interface + +Datasheets: + AMD datasheet not yet available, but almost everything can be found + in the publicly available ACPI 2.0 specification, which the adapter + follows. + +Author: Vojtech Pavlik <vojtech@suse.cz> + +Description +----------- + +If you see something like this:: + + 00:07.2 SMBus: Advanced Micro Devices [AMD] AMD-8111 SMBus 2.0 (rev 02) + Subsystem: Advanced Micro Devices [AMD] AMD-8111 SMBus 2.0 + Flags: medium devsel, IRQ 19 + I/O ports at d400 [size=32] + +in your ``lspci -v``, then this driver is for your chipset. + +Process Call Support +-------------------- + +Supported. + +SMBus 2.0 Support +----------------- + +Supported. Both PEC and block process call support is implemented. Slave +mode or host notification are not yet implemented. + +Notes +----- + +Note that for the 8111, there are two SMBus adapters. The SMBus 2.0 adapter +is supported by this driver, and the SMBus 1.0 adapter is supported by the +i2c-amd756 driver. diff --git a/Documentation/i2c/busses/i2c-diolan-u2c.rst b/Documentation/i2c/busses/i2c-diolan-u2c.rst new file mode 100644 index 0000000000..c18cbdcdf7 --- /dev/null +++ b/Documentation/i2c/busses/i2c-diolan-u2c.rst @@ -0,0 +1,29 @@ +============================ +Kernel driver i2c-diolan-u2c +============================ + +Supported adapters: + * Diolan U2C-12 I2C-USB adapter + + Documentation: + http://www.diolan.com/i2c/u2c12.html + +Author: Guenter Roeck <linux@roeck-us.net> + +Description +----------- + +This is the driver for the Diolan U2C-12 USB-I2C adapter. + +The Diolan U2C-12 I2C-USB Adapter provides a low cost solution to connect +a computer to I2C slave devices using a USB interface. It also supports +connectivity to SPI devices. + +This driver only supports the I2C interface of U2C-12. The driver does not use +interrupts. + + +Module parameters +----------------- + +* frequency: I2C bus frequency diff --git a/Documentation/i2c/busses/i2c-i801.rst b/Documentation/i2c/busses/i2c-i801.rst new file mode 100644 index 0000000000..10eced6c2e --- /dev/null +++ b/Documentation/i2c/busses/i2c-i801.rst @@ -0,0 +1,188 @@ +====================== +Kernel driver i2c-i801 +====================== + + +Supported adapters: + * Intel 82801AA and 82801AB (ICH and ICH0 - part of the + '810' and '810E' chipsets) + * Intel 82801BA (ICH2 - part of the '815E' chipset) + * Intel 82801CA/CAM (ICH3) + * Intel 82801DB (ICH4) (HW PEC supported) + * Intel 82801EB/ER (ICH5) (HW PEC supported) + * Intel 6300ESB + * Intel 82801FB/FR/FW/FRW (ICH6) + * Intel 82801G (ICH7) + * Intel 631xESB/632xESB (ESB2) + * Intel 82801H (ICH8) + * Intel 82801I (ICH9) + * Intel EP80579 (Tolapai) + * Intel 82801JI (ICH10) + * Intel 5/3400 Series (PCH) + * Intel 6 Series (PCH) + * Intel Patsburg (PCH) + * Intel DH89xxCC (PCH) + * Intel Panther Point (PCH) + * Intel Lynx Point (PCH) + * Intel Avoton (SOC) + * Intel Wellsburg (PCH) + * Intel Coleto Creek (PCH) + * Intel Wildcat Point (PCH) + * Intel BayTrail (SOC) + * Intel Braswell (SOC) + * Intel Sunrise Point (PCH) + * Intel Kaby Lake (PCH) + * Intel DNV (SOC) + * Intel Broxton (SOC) + * Intel Lewisburg (PCH) + * Intel Gemini Lake (SOC) + * Intel Cannon Lake (PCH) + * Intel Cedar Fork (PCH) + * Intel Ice Lake (PCH) + * Intel Comet Lake (PCH) + * Intel Elkhart Lake (PCH) + * Intel Tiger Lake (PCH) + * Intel Jasper Lake (SOC) + * Intel Emmitsburg (PCH) + * Intel Alder Lake (PCH) + * Intel Raptor Lake (PCH) + * Intel Meteor Lake (SOC and PCH) + * Intel Birch Stream (SOC) + + Datasheets: Publicly available at the Intel website + +On Intel Patsburg and later chipsets, both the normal host SMBus controller +and the additional 'Integrated Device Function' controllers are supported. + +Authors: + - Mark Studebaker <mdsxyz123@yahoo.com> + - Jean Delvare <jdelvare@suse.de> + + +Module Parameters +----------------- + +* disable_features (bit vector) + +Disable selected features normally supported by the device. This makes it +possible to work around possible driver or hardware bugs if the feature in +question doesn't work as intended for whatever reason. Bit values: + + ==== ========================================= + 0x01 disable SMBus PEC + 0x02 disable the block buffer + 0x08 disable the I2C block read functionality + 0x10 don't use interrupts + 0x20 disable SMBus Host Notify + ==== ========================================= + + +Description +----------- + +The ICH (properly known as the 82801AA), ICH0 (82801AB), ICH2 (82801BA), +ICH3 (82801CA/CAM) and later devices (PCH) are Intel chips that are a part of +Intel's '810' chipset for Celeron-based PCs, '810E' chipset for +Pentium-based PCs, '815E' chipset, and others. + +The ICH chips contain at least SEVEN separate PCI functions in TWO logical +PCI devices. An output of lspci will show something similar to the +following:: + + 00:1e.0 PCI bridge: Intel Corporation: Unknown device 2418 (rev 01) + 00:1f.0 ISA bridge: Intel Corporation: Unknown device 2410 (rev 01) + 00:1f.1 IDE interface: Intel Corporation: Unknown device 2411 (rev 01) + 00:1f.2 USB Controller: Intel Corporation: Unknown device 2412 (rev 01) + 00:1f.3 Unknown class [0c05]: Intel Corporation: Unknown device 2413 (rev 01) + +The SMBus controller is function 3 in device 1f. Class 0c05 is SMBus Serial +Controller. + +The ICH chips are quite similar to Intel's PIIX4 chip, at least in the +SMBus controller. + + +Process Call Support +-------------------- + +Block process call is supported on the 82801EB (ICH5) and later chips. + + +I2C Block Read Support +---------------------- + +I2C block read is supported on the 82801EB (ICH5) and later chips. + + +SMBus 2.0 Support +----------------- + +The 82801DB (ICH4) and later chips support several SMBus 2.0 features. + + +Interrupt Support +----------------- + +PCI interrupt support is supported on the 82801EB (ICH5) and later chips. + + +Hidden ICH SMBus +---------------- + +If your system has an Intel ICH south bridge, but you do NOT see the +SMBus device at 00:1f.3 in lspci, and you can't figure out any way in the +BIOS to enable it, it means it has been hidden by the BIOS code. Asus is +well known for first doing this on their P4B motherboard, and many other +boards after that. Some vendor machines are affected as well. + +The first thing to try is the "i2c-scmi" ACPI driver. It could be that the +SMBus was hidden on purpose because it'll be driven by ACPI. If the +i2c-scmi driver works for you, just forget about the i2c-i801 driver and +don't try to unhide the ICH SMBus. Even if i2c-scmi doesn't work, you +better make sure that the SMBus isn't used by the ACPI code. Try loading +the "fan" and "thermal" drivers, and check in /sys/class/thermal. If you +find a thermal zone with type "acpitz", it's likely that the ACPI is +accessing the SMBus and it's safer not to unhide it. Only once you are +certain that ACPI isn't using the SMBus, you can attempt to unhide it. + +In order to unhide the SMBus, we need to change the value of a PCI +register before the kernel enumerates the PCI devices. This is done in +drivers/pci/quirks.c, where all affected boards must be listed (see +function asus_hides_smbus_hostbridge.) If the SMBus device is missing, +and you think there's something interesting on the SMBus (e.g. a +hardware monitoring chip), you need to add your board to the list. + +The motherboard is identified using the subvendor and subdevice IDs of the +host bridge PCI device. Get yours with ``lspci -n -v -s 00:00.0``:: + + 00:00.0 Class 0600: 8086:2570 (rev 02) + Subsystem: 1043:80f2 + Flags: bus master, fast devsel, latency 0 + Memory at fc000000 (32-bit, prefetchable) [size=32M] + Capabilities: [e4] #09 [2106] + Capabilities: [a0] AGP version 3.0 + +Here the host bridge ID is 2570 (82865G/PE/P), the subvendor ID is 1043 +(Asus) and the subdevice ID is 80f2 (P4P800-X). You can find the symbolic +names for the bridge ID and the subvendor ID in include/linux/pci_ids.h, +and then add a case for your subdevice ID at the right place in +drivers/pci/quirks.c. Then please give it very good testing, to make sure +that the unhidden SMBus doesn't conflict with e.g. ACPI. + +If it works, proves useful (i.e. there are usable chips on the SMBus) +and seems safe, please submit a patch for inclusion into the kernel. + +Note: There's a useful script in lm_sensors 2.10.2 and later, named +unhide_ICH_SMBus (in prog/hotplug), which uses the fakephp driver to +temporarily unhide the SMBus without having to patch and recompile your +kernel. It's very convenient if you just want to check if there's +anything interesting on your hidden ICH SMBus. + + +---------------------------------------------------------------------------- + +The lm_sensors project gratefully acknowledges the support of Texas +Instruments in the initial development of this driver. + +The lm_sensors project gratefully acknowledges the support of Intel in the +development of SMBus 2.0 / ICH4 features of this driver. diff --git a/Documentation/i2c/busses/i2c-ismt.rst b/Documentation/i2c/busses/i2c-ismt.rst new file mode 100644 index 0000000000..8e74919a3f --- /dev/null +++ b/Documentation/i2c/busses/i2c-ismt.rst @@ -0,0 +1,44 @@ +====================== +Kernel driver i2c-ismt +====================== + + +Supported adapters: + * Intel S12xx series SOCs + +Authors: + Bill Brown <bill.e.brown@intel.com> + + +Module Parameters +----------------- + +* bus_speed (unsigned int) + +Allows changing of the bus speed. Normally, the bus speed is set by the BIOS +and never needs to be changed. However, some SMBus analyzers are too slow for +monitoring the bus during debug, thus the need for this module parameter. +Specify the bus speed in kHz. + +Available bus frequency settings: + + ==== ========= + 0 no change + 80 kHz + 100 kHz + 400 kHz + 1000 kHz + ==== ========= + + +Description +----------- + +The S12xx series of SOCs have a pair of integrated SMBus 2.0 controllers +targeted primarily at the microserver and storage markets. + +The S12xx series contain a pair of PCI functions. An output of lspci will show +something similar to the following:: + + 00:13.0 System peripheral: Intel Corporation Centerton SMBus 2.0 Controller 0 + 00:13.1 System peripheral: Intel Corporation Centerton SMBus 2.0 Controller 1 diff --git a/Documentation/i2c/busses/i2c-mlxcpld.rst b/Documentation/i2c/busses/i2c-mlxcpld.rst new file mode 100644 index 0000000000..9a0b2916aa --- /dev/null +++ b/Documentation/i2c/busses/i2c-mlxcpld.rst @@ -0,0 +1,57 @@ +================== +Driver i2c-mlxcpld +================== + +Author: Michael Shych <michaelsh@mellanox.com> + +This is the Mellanox I2C controller logic, implemented in Lattice CPLD +device. + +Device supports: + - Master mode. + - One physical bus. + - Polling mode. + +This controller is equipped within the next Mellanox systems: +"msx6710", "msx6720", "msb7700", "msn2700", "msx1410", "msn2410", "msb7800", +"msn2740", "msn2100". + +The next transaction types are supported: + - Receive Byte/Block. + - Send Byte/Block. + - Read Byte/Block. + - Write Byte/Block. + +Registers: + +=============== === ======================================================================= +CPBLTY 0x0 - capability reg. + Bits [6:5] - transaction length. b01 - 72B is supported, + 36B in other case. + Bit 7 - SMBus block read support. +CTRL 0x1 - control reg. + Resets all the registers. +HALF_CYC 0x4 - cycle reg. + Configure the width of I2C SCL half clock cycle (in 4 LPC_CLK + units). +I2C_HOLD 0x5 - hold reg. + OE (output enable) is delayed by value set to this register + (in LPC_CLK units) +CMD 0x6 - command reg. + Bit 0, 0 = write, 1 = read. + Bits [7:1] - the 7bit Address of the I2C device. + It should be written last as it triggers an I2C transaction. +NUM_DATA 0x7 - data size reg. + Number of data bytes to write in read transaction +NUM_ADDR 0x8 - address reg. + Number of address bytes to write in read transaction. +STATUS 0x9 - status reg. + Bit 0 - transaction is completed. + Bit 4 - ACK/NACK. +DATAx 0xa - 0x54 - 68 bytes data buffer regs. + For write transaction address is specified in four first bytes + (DATA1 - DATA4), data starting from DATA4. + For read transactions address is sent in a separate transaction and + specified in the four first bytes (DATA0 - DATA3). Data is read + starting from DATA0. +=============== === ======================================================================= diff --git a/Documentation/i2c/busses/i2c-nforce2.rst b/Documentation/i2c/busses/i2c-nforce2.rst new file mode 100644 index 0000000000..8318144526 --- /dev/null +++ b/Documentation/i2c/busses/i2c-nforce2.rst @@ -0,0 +1,53 @@ +========================= +Kernel driver i2c-nforce2 +========================= + +Supported adapters: + * nForce2 MCP 10de:0064 + * nForce2 Ultra 400 MCP 10de:0084 + * nForce3 Pro150 MCP 10de:00D4 + * nForce3 250Gb MCP 10de:00E4 + * nForce4 MCP 10de:0052 + * nForce4 MCP-04 10de:0034 + * nForce MCP51 10de:0264 + * nForce MCP55 10de:0368 + * nForce MCP61 10de:03EB + * nForce MCP65 10de:0446 + * nForce MCP67 10de:0542 + * nForce MCP73 10de:07D8 + * nForce MCP78S 10de:0752 + * nForce MCP79 10de:0AA2 + +Datasheet: + not publicly available, but seems to be similar to the + AMD-8111 SMBus 2.0 adapter. + +Authors: + - Hans-Frieder Vogt <hfvogt@gmx.net>, + - Thomas Leibold <thomas@plx.com>, + - Patrick Dreker <patrick@dreker.de> + +Description +----------- + +i2c-nforce2 is a driver for the SMBuses included in the nVidia nForce2 MCP. + +If your ``lspci -v`` listing shows something like the following:: + + 00:01.1 SMBus: nVidia Corporation: Unknown device 0064 (rev a2) + Subsystem: Asustek Computer, Inc.: Unknown device 0c11 + Flags: 66Mhz, fast devsel, IRQ 5 + I/O ports at c000 [size=32] + Capabilities: <available only to root> + +then this driver should support the SMBuses of your motherboard. + + +Notes +----- + +The SMBus adapter in the nForce2 chipset seems to be very similar to the +SMBus 2.0 adapter in the AMD-8111 south bridge. However, I could only get +the driver to work with direct I/O access, which is different to the EC +interface of the AMD-8111. Tested on Asus A7N8X. The ACPI DSDT table of the +Asus A7N8X lists two SMBuses, both of which are supported by this driver. diff --git a/Documentation/i2c/busses/i2c-nvidia-gpu.rst b/Documentation/i2c/busses/i2c-nvidia-gpu.rst new file mode 100644 index 0000000000..38fb8a4c87 --- /dev/null +++ b/Documentation/i2c/busses/i2c-nvidia-gpu.rst @@ -0,0 +1,20 @@ +============================ +Kernel driver i2c-nvidia-gpu +============================ + +Datasheet: not publicly available. + +Authors: + Ajay Gupta <ajayg@nvidia.com> + +Description +----------- + +i2c-nvidia-gpu is a driver for I2C controller included in NVIDIA Turing +and later GPUs and it is used to communicate with Type-C controller on GPUs. + +If your ``lspci -v`` listing shows something like the following:: + + 01:00.3 Serial bus controller [0c80]: NVIDIA Corporation Device 1ad9 (rev a1) + +then this driver should support the I2C controller of your GPU. diff --git a/Documentation/i2c/busses/i2c-ocores.rst b/Documentation/i2c/busses/i2c-ocores.rst new file mode 100644 index 0000000000..f5e175f2a2 --- /dev/null +++ b/Documentation/i2c/busses/i2c-ocores.rst @@ -0,0 +1,70 @@ +======================== +Kernel driver i2c-ocores +======================== + +Supported adapters: + * OpenCores.org I2C controller by Richard Herveille (see datasheet link) + https://opencores.org/project/i2c/overview + +Author: Peter Korsgaard <peter@korsgaard.com> + +Description +----------- + +i2c-ocores is an i2c bus driver for the OpenCores.org I2C controller +IP core by Richard Herveille. + +Usage +----- + +i2c-ocores uses the platform bus, so you need to provide a struct +platform_device with the base address and interrupt number. The +dev.platform_data of the device should also point to a struct +ocores_i2c_platform_data (see linux/platform_data/i2c-ocores.h) describing the +distance between registers and the input clock speed. +There is also a possibility to attach a list of i2c_board_info which +the i2c-ocores driver will add to the bus upon creation. + +E.G. something like:: + + static struct resource ocores_resources[] = { + [0] = { + .start = MYI2C_BASEADDR, + .end = MYI2C_BASEADDR + 8, + .flags = IORESOURCE_MEM, + }, + [1] = { + .start = MYI2C_IRQ, + .end = MYI2C_IRQ, + .flags = IORESOURCE_IRQ, + }, + }; + + /* optional board info */ + struct i2c_board_info ocores_i2c_board_info[] = { + { + I2C_BOARD_INFO("tsc2003", 0x48), + .platform_data = &tsc2003_platform_data, + .irq = TSC_IRQ + }, + { + I2C_BOARD_INFO("adv7180", 0x42 >> 1), + .irq = ADV_IRQ + } + }; + + static struct ocores_i2c_platform_data myi2c_data = { + .regstep = 2, /* two bytes between registers */ + .clock_khz = 50000, /* input clock of 50MHz */ + .devices = ocores_i2c_board_info, /* optional table of devices */ + .num_devices = ARRAY_SIZE(ocores_i2c_board_info), /* table size */ + }; + + static struct platform_device myi2c = { + .name = "ocores-i2c", + .dev = { + .platform_data = &myi2c_data, + }, + .num_resources = ARRAY_SIZE(ocores_resources), + .resource = ocores_resources, + }; diff --git a/Documentation/i2c/busses/i2c-parport.rst b/Documentation/i2c/busses/i2c-parport.rst new file mode 100644 index 0000000000..a9b4e81337 --- /dev/null +++ b/Documentation/i2c/busses/i2c-parport.rst @@ -0,0 +1,190 @@ +========================= +Kernel driver i2c-parport +========================= + +Author: Jean Delvare <jdelvare@suse.de> + +This is a unified driver for several i2c-over-parallel-port adapters, +such as the ones made by Philips, Velleman or ELV. This driver is +meant as a replacement for the older, individual drivers: + + * i2c-philips-par + * i2c-elv + * i2c-velleman + * video/i2c-parport + (NOT the same as this one, dedicated to home brew teletext adapters) + +It currently supports the following devices: + + * (type=0) Philips adapter + * (type=1) home brew teletext adapter + * (type=2) Velleman K8000 adapter + * (type=3) ELV adapter + * (type=4) Analog Devices ADM1032 evaluation board + * (type=5) Analog Devices evaluation boards: ADM1025, ADM1030, ADM1031 + * (type=6) Barco LPT->DVI (K5800236) adapter + * (type=7) One For All JP1 parallel port adapter + * (type=8) VCT-jig + +These devices use different pinout configurations, so you have to tell +the driver what you have, using the type module parameter. There is no +way to autodetect the devices. Support for different pinout configurations +can be easily added when needed. + +Earlier kernels defaulted to type=0 (Philips). But now, if the type +parameter is missing, the driver will simply fail to initialize. + +SMBus alert support is available on adapters which have this line properly +connected to the parallel port's interrupt pin. + + +Building your own adapter +------------------------- + +If you want to build you own i2c-over-parallel-port adapter, here is +a sample electronics schema (credits go to Sylvain Munaut):: + + Device PC + Side ___________________Vdd (+) Side + | | | + --- --- --- + | | | | | | + |R| |R| |R| + | | | | | | + --- --- --- + | | | + | | /| | + SCL ----------x--------o |-----------x------------------- pin 2 + | \| | | + | | | + | |\ | | + SDA ----------x----x---| o---x--------------------------- pin 13 + | |/ | + | | + | /| | + ---------o |----------------x-------------- pin 3 + \| | | + | | + --- --- + | | | | + |R| |R| + | | | | + --- --- + | | + ### ### + GND GND + +Remarks: + - This is the exact pinout and electronics used on the Analog Devices + evaluation boards. + - All inverters:: + + /| + -o |- + \| + + must be 74HC05, they must be open collector output. + - All resitors are 10k. + - Pins 18-25 of the parallel port connected to GND. + - Pins 4-9 (D2-D7) could be used as VDD is the driver drives them high. + The ADM1032 evaluation board uses D4-D7. Beware that the amount of + current you can draw from the parallel port is limited. Also note that + all connected lines MUST BE driven at the same state, else you'll short + circuit the output buffers! So plugging the I2C adapter after loading + the i2c-parport module might be a good safety since data line state + prior to init may be unknown. + - This is 5V! + - Obviously you cannot read SCL (so it's not really standard-compliant). + Pretty easy to add, just copy the SDA part and use another input pin. + That would give (ELV compatible pinout):: + + + Device PC + Side ______________________________Vdd (+) Side + | | | | + --- --- --- --- + | | | | | | | | + |R| |R| |R| |R| + | | | | | | | | + --- --- --- --- + | | | | + | | |\ | | + SCL ----------x--------x--| o---x------------------------ pin 15 + | | |/ | + | | | + | | /| | + | ---o |-------------x-------------- pin 2 + | \| | | + | | | + | | | + | |\ | | + SDA ---------------x---x--| o--------x------------------- pin 10 + | |/ | + | | + | /| | + ---o |------------------x--------- pin 3 + \| | | + | | + --- --- + | | | | + |R| |R| + | | | | + --- --- + | | + ### ### + GND GND + + +If possible, you should use the same pinout configuration as existing +adapters do, so you won't even have to change the code. + + +Similar (but different) drivers +------------------------------- + +This driver is NOT the same as the i2c-pport driver found in the i2c +package. The i2c-pport driver makes use of modern parallel port features so +that you don't need additional electronics. It has other restrictions +however, and was not ported to Linux 2.6 (yet). + +This driver is also NOT the same as the i2c-pcf-epp driver found in the +lm_sensors package. The i2c-pcf-epp driver doesn't use the parallel port as +an I2C bus directly. Instead, it uses it to control an external I2C bus +master. That driver was not ported to Linux 2.6 (yet) either. + + +Legacy documentation for Velleman adapter +----------------------------------------- + +Useful links: + +- Velleman http://www.velleman.be/ +- Velleman K8000 Howto http://howto.htlw16.ac.at/k8000-howto.html + +The project has lead to new libs for the Velleman K8000 and K8005: + + LIBK8000 v1.99.1 and LIBK8005 v0.21 + +With these libs, you can control the K8000 interface card and the K8005 +stepper motor card with the simple commands which are in the original +Velleman software, like SetIOchannel, ReadADchannel, SendStepCCWFull and +many more, using /dev/velleman. + + - http://home.wanadoo.nl/hihihi/libk8000.htm + - http://home.wanadoo.nl/hihihi/libk8005.htm + - http://struyve.mine.nu:8080/index.php?block=k8000 + - http://sourceforge.net/projects/libk8005/ + + +One For All JP1 parallel port adapter +------------------------------------- + +The JP1 project revolves around a set of remote controls which expose +the I2C bus their internal configuration EEPROM lives on via a 6 pin +jumper in the battery compartment. More details can be found at: + +http://www.hifi-remote.com/jp1/ + +Details of the simple parallel port hardware can be found at: + +http://www.hifi-remote.com/jp1/hardware.shtml diff --git a/Documentation/i2c/busses/i2c-pca-isa.rst b/Documentation/i2c/busses/i2c-pca-isa.rst new file mode 100644 index 0000000000..a254010c80 --- /dev/null +++ b/Documentation/i2c/busses/i2c-pca-isa.rst @@ -0,0 +1,26 @@ +========================= +Kernel driver i2c-pca-isa +========================= + +Supported adapters: + +This driver supports ISA boards using the Philips PCA 9564 +Parallel bus to I2C bus controller + +Author: Ian Campbell <icampbell@arcom.com>, Arcom Control Systems + +Module Parameters +----------------- + +* base int + I/O base address +* irq int + IRQ interrupt +* clock int + Clock rate as described in table 1 of PCA9564 datasheet + +Description +----------- + +This driver supports ISA boards using the Philips PCA 9564 +Parallel bus to I2C bus controller diff --git a/Documentation/i2c/busses/i2c-piix4.rst b/Documentation/i2c/busses/i2c-piix4.rst new file mode 100644 index 0000000000..07fe6f6f4b --- /dev/null +++ b/Documentation/i2c/busses/i2c-piix4.rst @@ -0,0 +1,111 @@ +======================= +Kernel driver i2c-piix4 +======================= + +Supported adapters: + * Intel 82371AB PIIX4 and PIIX4E + * Intel 82443MX (440MX) + Datasheet: Publicly available at the Intel website + * ServerWorks OSB4, CSB5, CSB6, HT-1000 and HT-1100 southbridges + Datasheet: Only available via NDA from ServerWorks + * ATI IXP200, IXP300, IXP400, SB600, SB700 and SB800 southbridges + Datasheet: Not publicly available + SB700 register reference available at: + http://support.amd.com/us/Embedded_TechDocs/43009_sb7xx_rrg_pub_1.00.pdf + * AMD SP5100 (SB700 derivative found on some server mainboards) + Datasheet: Publicly available at the AMD website + http://support.amd.com/us/Embedded_TechDocs/44413.pdf + * AMD Hudson-2, ML, CZ + Datasheet: Not publicly available + * Hygon CZ + Datasheet: Not publicly available + * Standard Microsystems (SMSC) SLC90E66 (Victory66) southbridge + Datasheet: Publicly available at the SMSC website http://www.smsc.com + +Authors: + - Frodo Looijaard <frodol@dds.nl> + - Philip Edelbrock <phil@netroedge.com> + + +Module Parameters +----------------- + +* force: int + Forcibly enable the PIIX4. DANGEROUS! +* force_addr: int + Forcibly enable the PIIX4 at the given address. EXTREMELY DANGEROUS! + + +Description +----------- + +The PIIX4 (properly known as the 82371AB) is an Intel chip with a lot of +functionality. Among other things, it implements the PCI bus. One of its +minor functions is implementing a System Management Bus. This is a true +SMBus - you can not access it on I2C levels. The good news is that it +natively understands SMBus commands and you do not have to worry about +timing problems. The bad news is that non-SMBus devices connected to it can +confuse it mightily. Yes, this is known to happen... + +Do ``lspci -v`` and see whether it contains an entry like this:: + + 0000:00:02.3 Bridge: Intel Corp. 82371AB/EB/MB PIIX4 ACPI (rev 02) + Flags: medium devsel, IRQ 9 + +Bus and device numbers may differ, but the function number must be +identical (like many PCI devices, the PIIX4 incorporates a number of +different 'functions', which can be considered as separate devices). If you +find such an entry, you have a PIIX4 SMBus controller. + +On some computers (most notably, some Dells), the SMBus is disabled by +default. If you use the insmod parameter 'force=1', the kernel module will +try to enable it. THIS IS VERY DANGEROUS! If the BIOS did not set up a +correct address for this module, you could get in big trouble (read: +crashes, data corruption, etc.). Try this only as a last resort (try BIOS +updates first, for example), and backup first! An even more dangerous +option is 'force_addr=<IOPORT>'. This will not only enable the PIIX4 like +'force' does, but it will also set a new base I/O port address. The SMBus +parts of the PIIX4 needs a range of 8 of these addresses to function +correctly. If these addresses are already reserved by some other device, +you will get into big trouble! DON'T USE THIS IF YOU ARE NOT VERY SURE +ABOUT WHAT YOU ARE DOING! + +The PIIX4E is just an new version of the PIIX4; it is supported as well. +The PIIX/PIIX3 does not implement an SMBus or I2C bus, so you can't use +this driver on those mainboards. + +The ServerWorks Southbridges, the Intel 440MX, and the Victory66 are +identical to the PIIX4 in I2C/SMBus support. + +The AMD SB700, SB800, SP5100 and Hudson-2 chipsets implement two +PIIX4-compatible SMBus controllers. If your BIOS initializes the +secondary controller, it will be detected by this driver as +an "Auxiliary SMBus Host Controller". + +If you own Force CPCI735 motherboard or other OSB4 based systems you may need +to change the SMBus Interrupt Select register so the SMBus controller uses +the SMI mode. + +1) Use ``lspci`` command and locate the PCI device with the SMBus controller: + 00:0f.0 ISA bridge: ServerWorks OSB4 South Bridge (rev 4f) + The line may vary for different chipsets. Please consult the driver source + for all possible PCI ids (and ``lspci -n`` to match them). Let's assume the + device is located at 00:0f.0. +2) Now you just need to change the value in 0xD2 register. Get it first with + command: ``lspci -xxx -s 00:0f.0`` + If the value is 0x3 then you need to change it to 0x1: + ``setpci -s 00:0f.0 d2.b=1`` + +Please note that you don't need to do that in all cases, just when the SMBus is +not working properly. + + +Hardware-specific issues +------------------------ + +This driver will refuse to load on IBM systems with an Intel PIIX4 SMBus. +Some of these machines have an RFID EEPROM (24RF08) connected to the SMBus, +which can easily get corrupted due to a state machine bug. These are mostly +Thinkpad laptops, but desktop systems may also be affected. We have no list +of all affected systems, so the only safe solution was to prevent access to +the SMBus on all IBM systems (detected using DMI data.) diff --git a/Documentation/i2c/busses/i2c-sis5595.rst b/Documentation/i2c/busses/i2c-sis5595.rst new file mode 100644 index 0000000000..b85630c84a --- /dev/null +++ b/Documentation/i2c/busses/i2c-sis5595.rst @@ -0,0 +1,68 @@ +========================= +Kernel driver i2c-sis5595 +========================= + +Authors: + - Frodo Looijaard <frodol@dds.nl>, + - Mark D. Studebaker <mdsxyz123@yahoo.com>, + - Philip Edelbrock <phil@netroedge.com> + +Supported adapters: + * Silicon Integrated Systems Corp. SiS5595 Southbridge + Datasheet: Publicly available at the Silicon Integrated Systems Corp. site. + +Note: all have mfr. ID 0x1039. + + ========= ====== + SUPPORTED PCI ID + ========= ====== + 5595 0008 + ========= ====== + + Note: these chips contain a 0008 device which is incompatible with the + 5595. We recognize these by the presence of the listed + "blacklist" PCI ID and refuse to load. + + ============= ====== ================ + NOT SUPPORTED PCI ID BLACKLIST PCI ID + ============= ====== ================ + 540 0008 0540 + 550 0008 0550 + 5513 0008 5511 + 5581 0008 5597 + 5582 0008 5597 + 5597 0008 5597 + 5598 0008 5597/5598 + 630 0008 0630 + 645 0008 0645 + 646 0008 0646 + 648 0008 0648 + 650 0008 0650 + 651 0008 0651 + 730 0008 0730 + 735 0008 0735 + 745 0008 0745 + 746 0008 0746 + ============= ====== ================ + +Module Parameters +----------------- + +================== ===================================================== +force_addr=0xaddr Set the I/O base address. Useful for boards + that don't set the address in the BIOS. Does not do a + PCI force; the device must still be present in lspci. + Don't use this unless the driver complains that the + base address is not set. +================== ===================================================== + +Description +----------- + +i2c-sis5595 is a true SMBus host driver for motherboards with the SiS5595 +southbridges. + +WARNING: If you are trying to access the integrated sensors on the SiS5595 +chip, you want the sis5595 driver for those, not this driver. This driver +is a BUS driver, not a CHIP driver. A BUS driver is used by other CHIP +drivers to access chips on the bus. diff --git a/Documentation/i2c/busses/i2c-sis630.rst b/Documentation/i2c/busses/i2c-sis630.rst new file mode 100644 index 0000000000..9fcd74b187 --- /dev/null +++ b/Documentation/i2c/busses/i2c-sis630.rst @@ -0,0 +1,63 @@ +======================== +Kernel driver i2c-sis630 +======================== + +Supported adapters: + * Silicon Integrated Systems Corp (SiS) + 630 chipset (Datasheet: available at http://www.sfr-fresh.com/linux) + 730 chipset + 964 chipset + * Possible other SiS chipsets ? + +Author: + - Alexander Malysh <amalysh@web.de> + - Amaury Decrême <amaury.decreme@gmail.com> - SiS964 support + +Module Parameters +----------------- + +================== ===================================================== +force = [1|0] Forcibly enable the SIS630. DANGEROUS! + This can be interesting for chipsets not named + above to check if it works for you chipset, + but DANGEROUS! + +high_clock = [1|0] Forcibly set Host Master Clock to 56KHz (default, + what your BIOS use). DANGEROUS! This should be a bit + faster, but freeze some systems (i.e. my Laptop). + SIS630/730 chip only. +================== ===================================================== + + +Description +----------- + +This SMBus only driver is known to work on motherboards with the above +named chipsets. + +If you see something like this:: + + 00:00.0 Host bridge: Silicon Integrated Systems [SiS] 630 Host (rev 31) + 00:01.0 ISA bridge: Silicon Integrated Systems [SiS] 85C503/5513 + +or like this:: + + 00:00.0 Host bridge: Silicon Integrated Systems [SiS] 730 Host (rev 02) + 00:01.0 ISA bridge: Silicon Integrated Systems [SiS] 85C503/5513 + +or like this:: + + 00:00.0 Host bridge: Silicon Integrated Systems [SiS] 760/M760 Host (rev 02) + 00:02.0 ISA bridge: Silicon Integrated Systems [SiS] SiS964 [MuTIOL Media IO] + LPC Controller (rev 36) + +in your ``lspci`` output , then this driver is for your chipset. + +Thank You +--------- +Philip Edelbrock <phil@netroedge.com> +- testing SiS730 support +Mark M. Hoffman <mhoffman@lightlink.com> +- bug fixes + +To anyone else which I forgot here ;), thanks! diff --git a/Documentation/i2c/busses/i2c-sis96x.rst b/Documentation/i2c/busses/i2c-sis96x.rst new file mode 100644 index 0000000000..437cc1d895 --- /dev/null +++ b/Documentation/i2c/busses/i2c-sis96x.rst @@ -0,0 +1,82 @@ +======================== +Kernel driver i2c-sis96x +======================== + +Replaces 2.4.x i2c-sis645 + +Supported adapters: + + * Silicon Integrated Systems Corp (SiS) + + Any combination of these host bridges: + 645, 645DX (aka 646), 648, 650, 651, 655, 735, 745, 746 + + and these south bridges: + 961, 962, 963(L) + +Author: Mark M. Hoffman <mhoffman@lightlink.com> + +Description +----------- + +This SMBus only driver is known to work on motherboards with the above +named chipset combinations. The driver was developed without benefit of a +proper datasheet from SiS. The SMBus registers are assumed compatible with +those of the SiS630, although they are located in a completely different +place. Thanks to Alexander Malysh <amalysh@web.de> for providing the +SiS630 datasheet (and driver). + +The command ``lspci`` as root should produce something like these lines:: + + 00:00.0 Host bridge: Silicon Integrated Systems [SiS]: Unknown device 0645 + 00:02.0 ISA bridge: Silicon Integrated Systems [SiS] 85C503/5513 + 00:02.1 SMBus: Silicon Integrated Systems [SiS]: Unknown device 0016 + +or perhaps this:: + + 00:00.0 Host bridge: Silicon Integrated Systems [SiS]: Unknown device 0645 + 00:02.0 ISA bridge: Silicon Integrated Systems [SiS]: Unknown device 0961 + 00:02.1 SMBus: Silicon Integrated Systems [SiS]: Unknown device 0016 + +(kernel versions later than 2.4.18 may fill in the "Unknown"s) + +If you can't see it please look on quirk_sis_96x_smbus +(drivers/pci/quirks.c) (also if southbridge detection fails) + +I suspect that this driver could be made to work for the following SiS +chipsets as well: 635, and 635T. If anyone owns a board with those chips +AND is willing to risk crashing & burning an otherwise well-behaved kernel +in the name of progress... please contact me at <mhoffman@lightlink.com> or +via the linux-i2c mailing list: <linux-i2c@vger.kernel.org>. Please send bug +reports and/or success stories as well. + + +TO DOs +------ + +* The driver does not support SMBus block reads/writes; I may add them if a + scenario is found where they're needed. + + +Thank You +--------- + +Mark D. Studebaker <mdsxyz123@yahoo.com> + - design hints and bug fixes + +Alexander Maylsh <amalysh@web.de> + - ditto, plus an important datasheet... almost the one I really wanted + +Hans-Günter Lütke Uphues <hg_lu@t-online.de> + - patch for SiS735 + +Robert Zwerus <arzie@dds.nl> + - testing for SiS645DX + +Kianusch Sayah Karadji <kianusch@sk-tech.net> + - patch for SiS645DX/962 + +Ken Healy + - patch for SiS655 + +To anyone else who has written w/ feedback, thanks! diff --git a/Documentation/i2c/busses/i2c-taos-evm.rst b/Documentation/i2c/busses/i2c-taos-evm.rst new file mode 100644 index 0000000000..f342e313ee --- /dev/null +++ b/Documentation/i2c/busses/i2c-taos-evm.rst @@ -0,0 +1,48 @@ +========================== +Kernel driver i2c-taos-evm +========================== + +Author: Jean Delvare <jdelvare@suse.de> + +This is a driver for the evaluation modules for TAOS I2C/SMBus chips. +The modules include an SMBus master with limited capabilities, which can +be controlled over the serial port. Virtually all evaluation modules +are supported, but a few lines of code need to be added for each new +module to instantiate the right I2C chip on the bus. Obviously, a driver +for the chip in question is also needed. + +Currently supported devices are: + +* TAOS TSL2550 EVM + +For additional information on TAOS products, please see + http://www.taosinc.com/ + + +Using this driver +----------------- + +In order to use this driver, you'll need the serport driver, and the +inputattach tool, which is part of the input-utils package. The following +commands will tell the kernel that you have a TAOS EVM on the first +serial port:: + + # modprobe serport + # inputattach --taos-evm /dev/ttyS0 + + +Technical details +----------------- + +Only 4 SMBus transaction types are supported by the TAOS evaluation +modules: +* Receive Byte +* Send Byte +* Read Byte +* Write Byte + +The communication protocol is text-based and pretty simple. It is +described in a PDF document on the CD which comes with the evaluation +module. The communication is rather slow, because the serial port has +to operate at 1200 bps. However, I don't think this is a big concern in +practice, as these modules are meant for evaluation and testing only. diff --git a/Documentation/i2c/busses/i2c-via.rst b/Documentation/i2c/busses/i2c-via.rst new file mode 100644 index 0000000000..846aa17d80 --- /dev/null +++ b/Documentation/i2c/busses/i2c-via.rst @@ -0,0 +1,40 @@ +===================== +Kernel driver i2c-via +===================== + +Supported adapters: + * VIA Technologies, InC. VT82C586B + Datasheet: Publicly available at the VIA website + +Author: Kyösti Mälkki <kmalkki@cc.hut.fi> + +Description +----------- + +i2c-via is an i2c bus driver for motherboards with VIA chipset. + +The following VIA pci chipsets are supported: + - MVP3, VP3, VP2/97, VPX/97 + - others with South bridge VT82C586B + +Your ``lspci`` listing must show this :: + + Bridge: VIA Technologies, Inc. VT82C586B ACPI (rev 10) + +Problems? +--------- + + Q: + You have VT82C586B on the motherboard, but not in the listing. + + A: + Go to your BIOS setup, section PCI devices or similar. + Turn USB support on, and try again. + + Q: + No error messages, but still i2c doesn't seem to work. + + A: + This can happen. This driver uses the pins VIA recommends in their + datasheets, but there are several ways the motherboard manufacturer + can actually wire the lines. diff --git a/Documentation/i2c/busses/i2c-viapro.rst b/Documentation/i2c/busses/i2c-viapro.rst new file mode 100644 index 0000000000..1762f0cf93 --- /dev/null +++ b/Documentation/i2c/busses/i2c-viapro.rst @@ -0,0 +1,77 @@ +======================== +Kernel driver i2c-viapro +======================== + +Supported adapters: + * VIA Technologies, Inc. VT82C596A/B + Datasheet: Sometimes available at the VIA website + + * VIA Technologies, Inc. VT82C686A/B + Datasheet: Sometimes available at the VIA website + + * VIA Technologies, Inc. VT8231, VT8233, VT8233A + Datasheet: available on request from VIA + + * VIA Technologies, Inc. VT8235, VT8237R, VT8237A, VT8237S, VT8251 + Datasheet: available on request and under NDA from VIA + + * VIA Technologies, Inc. CX700 + Datasheet: available on request and under NDA from VIA + + * VIA Technologies, Inc. VX800/VX820 + Datasheet: available on http://linux.via.com.tw + + * VIA Technologies, Inc. VX855/VX875 + Datasheet: available on http://linux.via.com.tw + + * VIA Technologies, Inc. VX900 + Datasheet: available on http://linux.via.com.tw + +Authors: + - Kyösti Mälkki <kmalkki@cc.hut.fi>, + - Mark D. Studebaker <mdsxyz123@yahoo.com>, + - Jean Delvare <jdelvare@suse.de> + +Module Parameters +----------------- + +* force: int + Forcibly enable the SMBus controller. DANGEROUS! +* force_addr: int + Forcibly enable the SMBus at the given address. EXTREMELY DANGEROUS! + +Description +----------- + +i2c-viapro is a true SMBus host driver for motherboards with one of the +supported VIA south bridges. + +Your ``lspci -n`` listing must show one of these : + + ================ ====================== + device 1106:3050 (VT82C596A function 3) + device 1106:3051 (VT82C596B function 3) + device 1106:3057 (VT82C686 function 4) + device 1106:3074 (VT8233) + device 1106:3147 (VT8233A) + device 1106:8235 (VT8231 function 4) + device 1106:3177 (VT8235) + device 1106:3227 (VT8237R) + device 1106:3337 (VT8237A) + device 1106:3372 (VT8237S) + device 1106:3287 (VT8251) + device 1106:8324 (CX700) + device 1106:8353 (VX800/VX820) + device 1106:8409 (VX855/VX875) + device 1106:8410 (VX900) + ================ ====================== + +If none of these show up, you should look in the BIOS for settings like +enable ACPI / SMBus or even USB. + +Except for the oldest chips (VT82C596A/B, VT82C686A and most probably +VT8231), this driver supports I2C block transactions. Such transactions +are mainly useful to read from and write to EEPROMs. + +The CX700/VX800/VX820 additionally appears to support SMBus PEC, although +this driver doesn't implement it yet. diff --git a/Documentation/i2c/busses/index.rst b/Documentation/i2c/busses/index.rst new file mode 100644 index 0000000000..5e4077b08d --- /dev/null +++ b/Documentation/i2c/busses/index.rst @@ -0,0 +1,32 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +I2C Bus Drivers +=============== + +.. toctree:: + :maxdepth: 1 + + i2c-ali1535 + i2c-ali1563 + i2c-ali15x3 + i2c-amd756 + i2c-amd8111 + i2c-amd-mp2 + i2c-diolan-u2c + i2c-i801 + i2c-ismt + i2c-mlxcpld + i2c-nforce2 + i2c-nvidia-gpu + i2c-ocores + i2c-parport + i2c-pca-isa + i2c-piix4 + i2c-sis5595 + i2c-sis630 + i2c-sis96x + i2c-taos-evm + i2c-viapro + i2c-via + scx200_acb diff --git a/Documentation/i2c/busses/scx200_acb.rst b/Documentation/i2c/busses/scx200_acb.rst new file mode 100644 index 0000000000..8dc7c35250 --- /dev/null +++ b/Documentation/i2c/busses/scx200_acb.rst @@ -0,0 +1,37 @@ +======================== +Kernel driver scx200_acb +======================== + +Author: Christer Weinigel <wingel@nano-system.com> + +The driver supersedes the older, never merged driver named i2c-nscacb. + +Module Parameters +----------------- + +* base: up to 4 ints + Base addresses for the ACCESS.bus controllers on SCx200 and SC1100 devices + + By default the driver uses two base addresses 0x820 and 0x840. + If you want only one base address, specify the second as 0 so as to + override this default. + +Description +----------- + +Enable the use of the ACCESS.bus controller on the Geode SCx200 and +SC1100 processors and the CS5535 and CS5536 Geode companion devices. + +Device-specific notes +--------------------- + +The SC1100 WRAP boards are known to use base addresses 0x810 and 0x820. +If the scx200_acb driver is built into the kernel, add the following +parameter to your boot command line:: + + scx200_acb.base=0x810,0x820 + +If the scx200_acb driver is built as a module, add the following line to +a configuration file in /etc/modprobe.d/ instead:: + + options scx200_acb base=0x810,0x820 diff --git a/Documentation/i2c/dev-interface.rst b/Documentation/i2c/dev-interface.rst new file mode 100644 index 0000000000..c277a8e120 --- /dev/null +++ b/Documentation/i2c/dev-interface.rst @@ -0,0 +1,221 @@ +============================================ +Implementing I2C device drivers in userspace +============================================ + +Usually, I2C devices are controlled by a kernel driver. But it is also +possible to access all devices on an adapter from userspace, through +the /dev interface. You need to load module i2c-dev for this. + +Each registered I2C adapter gets a number, counting from 0. You can +examine /sys/class/i2c-dev/ to see what number corresponds to which adapter. +Alternatively, you can run "i2cdetect -l" to obtain a formatted list of all +I2C adapters present on your system at a given time. i2cdetect is part of +the i2c-tools package. + +I2C device files are character device files with major device number 89 +and a minor device number corresponding to the number assigned as +explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ..., +i2c-10, ...). All 256 minor device numbers are reserved for I2C. + + +C example +========= + +So let's say you want to access an I2C adapter from a C program. +First, you need to include these two headers:: + + #include <linux/i2c-dev.h> + #include <i2c/smbus.h> + +Now, you have to decide which adapter you want to access. You should +inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this. +Adapter numbers are assigned somewhat dynamically, so you can not +assume much about them. They can even change from one boot to the next. + +Next thing, open the device file, as follows:: + + int file; + int adapter_nr = 2; /* probably dynamically determined */ + char filename[20]; + + snprintf(filename, 19, "/dev/i2c-%d", adapter_nr); + file = open(filename, O_RDWR); + if (file < 0) { + /* ERROR HANDLING; you can check errno to see what went wrong */ + exit(1); + } + +When you have opened the device, you must specify with what device +address you want to communicate:: + + int addr = 0x40; /* The I2C address */ + + if (ioctl(file, I2C_SLAVE, addr) < 0) { + /* ERROR HANDLING; you can check errno to see what went wrong */ + exit(1); + } + +Well, you are all set up now. You can now use SMBus commands or plain +I2C to communicate with your device. SMBus commands are preferred if +the device supports them. Both are illustrated below:: + + __u8 reg = 0x10; /* Device register to access */ + __s32 res; + char buf[10]; + + /* Using SMBus commands */ + res = i2c_smbus_read_word_data(file, reg); + if (res < 0) { + /* ERROR HANDLING: I2C transaction failed */ + } else { + /* res contains the read word */ + } + + /* + * Using I2C Write, equivalent of + * i2c_smbus_write_word_data(file, reg, 0x6543) + */ + buf[0] = reg; + buf[1] = 0x43; + buf[2] = 0x65; + if (write(file, buf, 3) != 3) { + /* ERROR HANDLING: I2C transaction failed */ + } + + /* Using I2C Read, equivalent of i2c_smbus_read_byte(file) */ + if (read(file, buf, 1) != 1) { + /* ERROR HANDLING: I2C transaction failed */ + } else { + /* buf[0] contains the read byte */ + } + +Note that only a subset of the I2C and SMBus protocols can be achieved by +the means of read() and write() calls. In particular, so-called combined +transactions (mixing read and write messages in the same transaction) +aren't supported. For this reason, this interface is almost never used by +user-space programs. + +IMPORTANT: because of the use of inline functions, you *have* to use +'-O' or some variation when you compile your program! + + +Full interface description +========================== + +The following IOCTLs are defined: + +``ioctl(file, I2C_SLAVE, long addr)`` + Change slave address. The address is passed in the 7 lower bits of the + argument (except for 10 bit addresses, passed in the 10 lower bits in this + case). + +``ioctl(file, I2C_TENBIT, long select)`` + Selects ten bit addresses if select not equals 0, selects normal 7 bit + addresses if select equals 0. Default 0. This request is only valid + if the adapter has I2C_FUNC_10BIT_ADDR. + +``ioctl(file, I2C_PEC, long select)`` + Selects SMBus PEC (packet error checking) generation and verification + if select not equals 0, disables if select equals 0. Default 0. + Used only for SMBus transactions. This request only has an effect if the + the adapter has I2C_FUNC_SMBUS_PEC; it is still safe if not, it just + doesn't have any effect. + +``ioctl(file, I2C_FUNCS, unsigned long *funcs)`` + Gets the adapter functionality and puts it in ``*funcs``. + +``ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset)`` + Do combined read/write transaction without stop in between. + Only valid if the adapter has I2C_FUNC_I2C. The argument is + a pointer to a:: + + struct i2c_rdwr_ioctl_data { + struct i2c_msg *msgs; /* ptr to array of simple messages */ + int nmsgs; /* number of messages to exchange */ + } + + The msgs[] themselves contain further pointers into data buffers. + The function will write or read data to or from that buffers depending + on whether the I2C_M_RD flag is set in a particular message or not. + The slave address and whether to use ten bit address mode has to be + set in each message, overriding the values set with the above ioctl's. + +``ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args)`` + If possible, use the provided ``i2c_smbus_*`` methods described below instead + of issuing direct ioctls. + +You can do plain I2C transactions by using read(2) and write(2) calls. +You do not need to pass the address byte; instead, set it through +ioctl I2C_SLAVE before you try to access the device. + +You can do SMBus level transactions (see documentation file smbus-protocol.rst +for details) through the following functions:: + + __s32 i2c_smbus_write_quick(int file, __u8 value); + __s32 i2c_smbus_read_byte(int file); + __s32 i2c_smbus_write_byte(int file, __u8 value); + __s32 i2c_smbus_read_byte_data(int file, __u8 command); + __s32 i2c_smbus_write_byte_data(int file, __u8 command, __u8 value); + __s32 i2c_smbus_read_word_data(int file, __u8 command); + __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value); + __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value); + __s32 i2c_smbus_block_process_call(int file, __u8 command, __u8 length, + __u8 *values); + __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values); + __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, + __u8 *values); + +All these transactions return -1 on failure; you can read errno to see +what happened. The 'write' transactions return 0 on success; the +'read' transactions return the read value, except for read_block, which +returns the number of values read. The block buffers need not be longer +than 32 bytes. + +The above functions are made available by linking against the libi2c library, +which is provided by the i2c-tools project. See: +https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/. + + +Implementation details +====================== + +For the interested, here's the code flow which happens inside the kernel +when you use the /dev interface to I2C: + +1) Your program opens /dev/i2c-N and calls ioctl() on it, as described in + section "C example" above. + +2) These open() and ioctl() calls are handled by the i2c-dev kernel + driver: see i2c-dev.c:i2cdev_open() and i2c-dev.c:i2cdev_ioctl(), + respectively. You can think of i2c-dev as a generic I2C chip driver + that can be programmed from user-space. + +3) Some ioctl() calls are for administrative tasks and are handled by + i2c-dev directly. Examples include I2C_SLAVE (set the address of the + device you want to access) and I2C_PEC (enable or disable SMBus error + checking on future transactions.) + +4) Other ioctl() calls are converted to in-kernel function calls by + i2c-dev. Examples include I2C_FUNCS, which queries the I2C adapter + functionality using i2c.h:i2c_get_functionality(), and I2C_SMBUS, which + performs an SMBus transaction using i2c-core-smbus.c:i2c_smbus_xfer(). + + The i2c-dev driver is responsible for checking all the parameters that + come from user-space for validity. After this point, there is no + difference between these calls that came from user-space through i2c-dev + and calls that would have been performed by kernel I2C chip drivers + directly. This means that I2C bus drivers don't need to implement + anything special to support access from user-space. + +5) These i2c.h functions are wrappers to the actual implementation of + your I2C bus driver. Each adapter must declare callback functions + implementing these standard calls. i2c.h:i2c_get_functionality() calls + i2c_adapter.algo->functionality(), while + i2c-core-smbus.c:i2c_smbus_xfer() calls either + adapter.algo->smbus_xfer() if it is implemented, or if not, + i2c-core-smbus.c:i2c_smbus_xfer_emulated() which in turn calls + i2c_adapter.algo->master_xfer(). + +After your I2C bus driver has processed these requests, execution runs +up the call chain, with almost no processing done, except by i2c-dev to +package the returned data, if any, in suitable format for the ioctl. diff --git a/Documentation/i2c/dma-considerations.rst b/Documentation/i2c/dma-considerations.rst new file mode 100644 index 0000000000..142d52ce9e --- /dev/null +++ b/Documentation/i2c/dma-considerations.rst @@ -0,0 +1,71 @@ +================= +Linux I2C and DMA +================= + +Given that I2C is a low-speed bus, over which the majority of messages +transferred are small, it is not considered a prime user of DMA access. At this +time of writing, only 10% of I2C bus master drivers have DMA support +implemented. And the vast majority of transactions are so small that setting up +DMA for it will likely add more overhead than a plain PIO transfer. + +Therefore, it is *not* mandatory that the buffer of an I2C message is DMA safe. +It does not seem reasonable to apply additional burdens when the feature is so +rarely used. However, it is recommended to use a DMA-safe buffer if your +message size is likely applicable for DMA. Most drivers have this threshold +around 8 bytes (as of today, this is mostly an educated guess, however). For +any message of 16 byte or larger, it is probably a really good idea. Please +note that other subsystems you use might add requirements. E.g., if your +I2C bus master driver is using USB as a bridge, then you need to have DMA +safe buffers always, because USB requires it. + +Clients +------- + +For clients, if you use a DMA safe buffer in i2c_msg, set the I2C_M_DMA_SAFE +flag with it. Then, the I2C core and drivers know they can safely operate DMA +on it. Note that using this flag is optional. I2C host drivers which are not +updated to use this flag will work like before. And like before, they risk +using an unsafe DMA buffer. To improve this situation, using I2C_M_DMA_SAFE in +more and more clients and host drivers is the planned way forward. Note also +that setting this flag makes only sense in kernel space. User space data is +copied into kernel space anyhow. The I2C core makes sure the destination +buffers in kernel space are always DMA capable. Also, when the core emulates +SMBus transactions via I2C, the buffers for block transfers are DMA safe. Users +of i2c_master_send() and i2c_master_recv() functions can now use DMA safe +variants (i2c_master_send_dmasafe() and i2c_master_recv_dmasafe()) once they +know their buffers are DMA safe. Users of i2c_transfer() must set the +I2C_M_DMA_SAFE flag manually. + +Masters +------- + +Bus master drivers wishing to implement safe DMA can use helper functions from +the I2C core. One gives you a DMA-safe buffer for a given i2c_msg as long as a +certain threshold is met:: + + dma_buf = i2c_get_dma_safe_msg_buf(msg, threshold_in_byte); + +If a buffer is returned, it is either msg->buf for the I2C_M_DMA_SAFE case or a +bounce buffer. But you don't need to care about that detail, just use the +returned buffer. If NULL is returned, the threshold was not met or a bounce +buffer could not be allocated. Fall back to PIO in that case. + +In any case, a buffer obtained from above needs to be released. Another helper +function ensures a potentially used bounce buffer is freed:: + + i2c_put_dma_safe_msg_buf(dma_buf, msg, xferred); + +The last argument 'xferred' controls if the buffer is synced back to the +message or not. No syncing is needed in cases setting up DMA had an error and +there was no data transferred. + +The bounce buffer handling from the core is generic and simple. It will always +allocate a new bounce buffer. If you want a more sophisticated handling (e.g. +reusing pre-allocated buffers), you are free to implement your own. + +Please also check the in-kernel documentation for details. The i2c-sh_mobile +driver can be used as a reference example how to use the above helpers. + +Final note: If you plan to use DMA with I2C (or with anything else, actually) +make sure you have CONFIG_DMA_API_DEBUG enabled during development. It can help +you find various issues which can be complex to debug otherwise. diff --git a/Documentation/i2c/fault-codes.rst b/Documentation/i2c/fault-codes.rst new file mode 100644 index 0000000000..80b14e718b --- /dev/null +++ b/Documentation/i2c/fault-codes.rst @@ -0,0 +1,131 @@ +===================== +I2C/SMBUS Fault Codes +===================== + +This is a summary of the most important conventions for use of fault +codes in the I2C/SMBus stack. + + +A "Fault" is not always an "Error" +---------------------------------- +Not all fault reports imply errors; "page faults" should be a familiar +example. Software often retries idempotent operations after transient +faults. There may be fancier recovery schemes that are appropriate in +some cases, such as re-initializing (and maybe resetting). After such +recovery, triggered by a fault report, there is no error. + +In a similar way, sometimes a "fault" code just reports one defined +result for an operation ... it doesn't indicate that anything is wrong +at all, just that the outcome wasn't on the "golden path". + +In short, your I2C driver code may need to know these codes in order +to respond correctly. Other code may need to rely on YOUR code reporting +the right fault code, so that it can (in turn) behave correctly. + + +I2C and SMBus fault codes +------------------------- +These are returned as negative numbers from most calls, with zero or +some positive number indicating a non-fault return. The specific +numbers associated with these symbols differ between architectures, +though most Linux systems use <asm-generic/errno*.h> numbering. + +Note that the descriptions here are not exhaustive. There are other +codes that may be returned, and other cases where these codes should +be returned. However, drivers should not return other codes for these +cases (unless the hardware doesn't provide unique fault reports). + +Also, codes returned by adapter probe methods follow rules which are +specific to their host bus (such as PCI, or the platform bus). + + +EAGAIN + Returned by I2C adapters when they lose arbitration in master + transmit mode: some other master was transmitting different + data at the same time. + + Also returned when trying to invoke an I2C operation in an + atomic context, when some task is already using that I2C bus + to execute some other operation. + +EBADMSG + Returned by SMBus logic when an invalid Packet Error Code byte + is received. This code is a CRC covering all bytes in the + transaction, and is sent before the terminating STOP. This + fault is only reported on read transactions; the SMBus slave + may have a way to report PEC mismatches on writes from the + host. Note that even if PECs are in use, you should not rely + on these as the only way to detect incorrect data transfers. + +EBUSY + Returned by SMBus adapters when the bus was busy for longer + than allowed. This usually indicates some device (maybe the + SMBus adapter) needs some fault recovery (such as resetting), + or that the reset was attempted but failed. + +EINVAL + This rather vague error means an invalid parameter has been + detected before any I/O operation was started. Use a more + specific fault code when you can. + +EIO + This rather vague error means something went wrong when + performing an I/O operation. Use a more specific fault + code when you can. + +ENODEV + Returned by driver probe() methods. This is a bit more + specific than ENXIO, implying the problem isn't with the + address, but with the device found there. Driver probes + may verify the device returns *correct* responses, and + return this as appropriate. (The driver core will warn + about probe faults other than ENXIO and ENODEV.) + +ENOMEM + Returned by any component that can't allocate memory when + it needs to do so. + +ENXIO + Returned by I2C adapters to indicate that the address phase + of a transfer didn't get an ACK. While it might just mean + an I2C device was temporarily not responding, usually it + means there's nothing listening at that address. + + Returned by driver probe() methods to indicate that they + found no device to bind to. (ENODEV may also be used.) + +EOPNOTSUPP + Returned by an adapter when asked to perform an operation + that it doesn't, or can't, support. + + For example, this would be returned when an adapter that + doesn't support SMBus block transfers is asked to execute + one. In that case, the driver making that request should + have verified that functionality was supported before it + made that block transfer request. + + Similarly, if an I2C adapter can't execute all legal I2C + messages, it should return this when asked to perform a + transaction it can't. (These limitations can't be seen in + the adapter's functionality mask, since the assumption is + that if an adapter supports I2C it supports all of I2C.) + +EPROTO + Returned when slave does not conform to the relevant I2C + or SMBus (or chip-specific) protocol specifications. One + case is when the length of an SMBus block data response + (from the SMBus slave) is outside the range 1-32 bytes. + +ESHUTDOWN + Returned when a transfer was requested using an adapter + which is already suspended. + +ETIMEDOUT + This is returned by drivers when an operation took too much + time, and was aborted before it completed. + + SMBus adapters may return it when an operation took more + time than allowed by the SMBus specification; for example, + when a slave stretches clocks too far. I2C has no such + timeouts, but it's normal for I2C adapters to impose some + arbitrary limits (much longer than SMBus!) too. diff --git a/Documentation/i2c/functionality.rst b/Documentation/i2c/functionality.rst new file mode 100644 index 0000000000..377507c561 --- /dev/null +++ b/Documentation/i2c/functionality.rst @@ -0,0 +1,156 @@ +======================= +I2C/SMBus Functionality +======================= + +INTRODUCTION +------------ + +Because not every I2C or SMBus adapter implements everything in the +I2C specifications, a client can not trust that everything it needs +is implemented when it is given the option to attach to an adapter: +the client needs some way to check whether an adapter has the needed +functionality. + + +FUNCTIONALITY CONSTANTS +----------------------- + +For the most up-to-date list of functionality constants, please check +<uapi/linux/i2c.h>! + + =============================== ============================================== + I2C_FUNC_I2C Plain i2c-level commands (Pure SMBus + adapters typically can not do these) + I2C_FUNC_10BIT_ADDR Handles the 10-bit address extensions + I2C_FUNC_PROTOCOL_MANGLING Knows about the I2C_M_IGNORE_NAK, + I2C_M_REV_DIR_ADDR and I2C_M_NO_RD_ACK + flags (which modify the I2C protocol!) + I2C_FUNC_NOSTART Can skip repeated start sequence + I2C_FUNC_SMBUS_QUICK Handles the SMBus write_quick command + I2C_FUNC_SMBUS_READ_BYTE Handles the SMBus read_byte command + I2C_FUNC_SMBUS_WRITE_BYTE Handles the SMBus write_byte command + I2C_FUNC_SMBUS_READ_BYTE_DATA Handles the SMBus read_byte_data command + I2C_FUNC_SMBUS_WRITE_BYTE_DATA Handles the SMBus write_byte_data command + I2C_FUNC_SMBUS_READ_WORD_DATA Handles the SMBus read_word_data command + I2C_FUNC_SMBUS_WRITE_WORD_DATA Handles the SMBus write_byte_data command + I2C_FUNC_SMBUS_PROC_CALL Handles the SMBus process_call command + I2C_FUNC_SMBUS_READ_BLOCK_DATA Handles the SMBus read_block_data command + I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command + I2C_FUNC_SMBUS_READ_I2C_BLOCK Handles the SMBus read_i2c_block_data command + I2C_FUNC_SMBUS_WRITE_I2C_BLOCK Handles the SMBus write_i2c_block_data command + =============================== ============================================== + +A few combinations of the above flags are also defined for your convenience: + + ========================= ====================================== + I2C_FUNC_SMBUS_BYTE Handles the SMBus read_byte + and write_byte commands + I2C_FUNC_SMBUS_BYTE_DATA Handles the SMBus read_byte_data + and write_byte_data commands + I2C_FUNC_SMBUS_WORD_DATA Handles the SMBus read_word_data + and write_word_data commands + I2C_FUNC_SMBUS_BLOCK_DATA Handles the SMBus read_block_data + and write_block_data commands + I2C_FUNC_SMBUS_I2C_BLOCK Handles the SMBus read_i2c_block_data + and write_i2c_block_data commands + I2C_FUNC_SMBUS_EMUL Handles all SMBus commands that can be + emulated by a real I2C adapter (using + the transparent emulation layer) + ========================= ====================================== + +In kernel versions prior to 3.5 I2C_FUNC_NOSTART was implemented as +part of I2C_FUNC_PROTOCOL_MANGLING. + + +ADAPTER IMPLEMENTATION +---------------------- + +When you write a new adapter driver, you will have to implement a +function callback ``functionality``. Typical implementations are given +below. + +A typical SMBus-only adapter would list all the SMBus transactions it +supports. This example comes from the i2c-piix4 driver:: + + static u32 piix4_func(struct i2c_adapter *adapter) + { + return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | + I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | + I2C_FUNC_SMBUS_BLOCK_DATA; + } + +A typical full-I2C adapter would use the following (from the i2c-pxa +driver):: + + static u32 i2c_pxa_functionality(struct i2c_adapter *adap) + { + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL; + } + +I2C_FUNC_SMBUS_EMUL includes all the SMBus transactions (with the +addition of I2C block transactions) which i2c-core can emulate using +I2C_FUNC_I2C without any help from the adapter driver. The idea is +to let the client drivers check for the support of SMBus functions +without having to care whether the said functions are implemented in +hardware by the adapter, or emulated in software by i2c-core on top +of an I2C adapter. + + +CLIENT CHECKING +--------------- + +Before a client tries to attach to an adapter, or even do tests to check +whether one of the devices it supports is present on an adapter, it should +check whether the needed functionality is present. The typical way to do +this is (from the lm75 driver):: + + static int lm75_detect(...) + { + (...) + if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA | + I2C_FUNC_SMBUS_WORD_DATA)) + goto exit; + (...) + } + +Here, the lm75 driver checks if the adapter can do both SMBus byte data +and SMBus word data transactions. If not, then the driver won't work on +this adapter and there's no point in going on. If the check above is +successful, then the driver knows that it can call the following +functions: i2c_smbus_read_byte_data(), i2c_smbus_write_byte_data(), +i2c_smbus_read_word_data() and i2c_smbus_write_word_data(). As a rule of +thumb, the functionality constants you test for with +i2c_check_functionality() should match exactly the i2c_smbus_* functions +which you driver is calling. + +Note that the check above doesn't tell whether the functionalities are +implemented in hardware by the underlying adapter or emulated in +software by i2c-core. Client drivers don't have to care about this, as +i2c-core will transparently implement SMBus transactions on top of I2C +adapters. + + +CHECKING THROUGH /DEV +--------------------- + +If you try to access an adapter from a userspace program, you will have +to use the /dev interface. You will still have to check whether the +functionality you need is supported, of course. This is done using +the I2C_FUNCS ioctl. An example, adapted from the i2cdetect program, is +below:: + + int file; + if (file = open("/dev/i2c-0", O_RDWR) < 0) { + /* Some kind of error handling */ + exit(1); + } + if (ioctl(file, I2C_FUNCS, &funcs) < 0) { + /* Some kind of error handling */ + exit(1); + } + if (!(funcs & I2C_FUNC_SMBUS_QUICK)) { + /* Oops, the needed functionality (SMBus write_quick function) is + not available! */ + exit(1); + } + /* Now it is safe to use the SMBus write_quick command */ diff --git a/Documentation/i2c/gpio-fault-injection.rst b/Documentation/i2c/gpio-fault-injection.rst new file mode 100644 index 0000000000..91d23889ab --- /dev/null +++ b/Documentation/i2c/gpio-fault-injection.rst @@ -0,0 +1,136 @@ +========================= +Linux I2C fault injection +========================= + +The GPIO based I2C bus master driver can be configured to provide fault +injection capabilities. It is then meant to be connected to another I2C bus +which is driven by the I2C bus master driver under test. The GPIO fault +injection driver can create special states on the bus which the other I2C bus +master driver should handle gracefully. + +Once the Kconfig option I2C_GPIO_FAULT_INJECTOR is enabled, there will be an +'i2c-fault-injector' subdirectory in the Kernel debugfs filesystem, usually +mounted at /sys/kernel/debug. There will be a separate subdirectory per GPIO +driven I2C bus. Each subdirectory will contain files to trigger the fault +injection. They will be described now along with their intended use-cases. + +Wire states +=========== + +"scl" +----- + +By reading this file, you get the current state of SCL. By writing, you can +change its state to either force it low or to release it again. So, by using +"echo 0 > scl" you force SCL low and thus, no communication will be possible +because the bus master under test will not be able to clock. It should detect +the condition of SCL being unresponsive and report an error to the upper +layers. + +"sda" +----- + +By reading this file, you get the current state of SDA. By writing, you can +change its state to either force it low or to release it again. So, by using +"echo 0 > sda" you force SDA low and thus, data cannot be transmitted. The bus +master under test should detect this condition and trigger a bus recovery (see +I2C specification version 4, section 3.1.16) using the helpers of the Linux I2C +core (see 'struct bus_recovery_info'). However, the bus recovery will not +succeed because SDA is still pinned low until you manually release it again +with "echo 1 > sda". A test with an automatic release can be done with the +"incomplete transfers" class of fault injectors. + +Incomplete transfers +==================== + +The following fault injectors create situations where SDA will be held low by a +device. Bus recovery should be able to fix these situations. But please note: +there are I2C client devices which detect a stuck SDA on their side and release +it on their own after a few milliseconds. Also, there might be an external +device deglitching and monitoring the I2C bus. It could also detect a stuck SDA +and will init a bus recovery on its own. If you want to implement bus recovery +in a bus master driver, make sure you checked your hardware setup for such +devices before. And always verify with a scope or logic analyzer! + +"incomplete_address_phase" +-------------------------- + +This file is write only and you need to write the address of an existing I2C +client device to it. Then, a read transfer to this device will be started, but +it will stop at the ACK phase after the address of the client has been +transmitted. Because the device will ACK its presence, this results in SDA +being pulled low by the device while SCL is high. So, similar to the "sda" file +above, the bus master under test should detect this condition and try a bus +recovery. This time, however, it should succeed and the device should release +SDA after toggling SCL. + +"incomplete_write_byte" +----------------------- + +Similar to above, this file is write only and you need to write the address of +an existing I2C client device to it. + +The injector will again stop at one ACK phase, so the device will keep SDA low +because it acknowledges data. However, there are two differences compared to +'incomplete_address_phase': + +a) the message sent out will be a write message +b) after the address byte, a 0x00 byte will be transferred. Then, stop at ACK. + +This is a highly delicate state, the device is set up to write any data to +register 0x00 (if it has registers) when further clock pulses happen on SCL. +This is why bus recovery (up to 9 clock pulses) must either check SDA or send +additional STOP conditions to ensure the bus has been released. Otherwise +random data will be written to a device! + +Lost arbitration +================ + +Here, we want to simulate the condition where the master under test loses the +bus arbitration against another master in a multi-master setup. + +"lose_arbitration" +------------------ + +This file is write only and you need to write the duration of the arbitration +interference (in µs, maximum is 100ms). The calling process will then sleep +and wait for the next bus clock. The process is interruptible, though. + +Arbitration lost is achieved by waiting for SCL going down by the master under +test and then pulling SDA low for some time. So, the I2C address sent out +should be corrupted and that should be detected properly. That means that the +address sent out should have a lot of '1' bits to be able to detect corruption. +There doesn't need to be a device at this address because arbitration lost +should be detected beforehand. Also note, that SCL going down is monitored +using interrupts, so the interrupt latency might cause the first bits to be not +corrupted. A good starting point for using this fault injector on an otherwise +idle bus is:: + + # echo 200 > lose_arbitration & + # i2cget -y <bus_to_test> 0x3f + +Panic during transfer +===================== + +This fault injector will create a Kernel panic once the master under test +started a transfer. This usually means that the state machine of the bus master +driver will be ungracefully interrupted and the bus may end up in an unusual +state. Use this to check if your shutdown/reboot/boot code can handle this +scenario. + +"inject_panic" +-------------- + +This file is write only and you need to write the delay between the detected +start of a transmission and the induced Kernel panic (in µs, maximum is 100ms). +The calling process will then sleep and wait for the next bus clock. The +process is interruptible, though. + +Start of a transfer is detected by waiting for SCL going down by the master +under test. A good starting point for using this fault injector is:: + + # echo 0 > inject_panic & + # i2cget -y <bus_to_test> <some_address> + +Note that there doesn't need to be a device listening to the address you are +using. Results may vary depending on that, though. diff --git a/Documentation/i2c/i2c-address-translators.rst b/Documentation/i2c/i2c-address-translators.rst new file mode 100644 index 0000000000..b22ce9f41e --- /dev/null +++ b/Documentation/i2c/i2c-address-translators.rst @@ -0,0 +1,96 @@ +.. SPDX-License-Identifier: GPL-2.0 + +======================= +I2C Address Translators +======================= + +Author: Luca Ceresoli <luca@lucaceresoli.net> +Author: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com> + +Description +----------- + +An I2C Address Translator (ATR) is a device with an I2C slave parent +("upstream") port and N I2C master child ("downstream") ports, and +forwards transactions from upstream to the appropriate downstream port +with a modified slave address. The address used on the parent bus is +called the "alias" and is (potentially) different from the physical +slave address of the child bus. Address translation is done by the +hardware. + +An ATR looks similar to an i2c-mux except: + - the address on the parent and child busses can be different + - there is normally no need to select the child port; the alias used on the + parent bus implies it + +The ATR functionality can be provided by a chip with many other features. +The kernel i2c-atr provides a helper to implement an ATR within a driver. + +The ATR creates a new I2C "child" adapter on each child bus. Adding +devices on the child bus ends up in invoking the driver code to select +an available alias. Maintaining an appropriate pool of available aliases +and picking one for each new device is up to the driver implementer. The +ATR maintains a table of currently assigned alias and uses it to modify +all I2C transactions directed to devices on the child buses. + +A typical example follows. + +Topology:: + + Slave X @ 0x10 + .-----. | + .-----. | |---+---- B + | CPU |--A--| ATR | + `-----' | |---+---- C + `-----' | + Slave Y @ 0x10 + +Alias table: + +A, B and C are three physical I2C busses, electrically independent from +each other. The ATR receives the transactions initiated on bus A and +propagates them on bus B or bus C or none depending on the device address +in the transaction and based on the alias table. + +Alias table: + +.. table:: + + =============== ===== + Client Alias + =============== ===== + X (bus B, 0x10) 0x20 + Y (bus C, 0x10) 0x30 + =============== ===== + +Transaction: + + - Slave X driver requests a transaction (on adapter B), slave address 0x10 + - ATR driver finds slave X is on bus B and has alias 0x20, rewrites + messages with address 0x20, forwards to adapter A + - Physical I2C transaction on bus A, slave address 0x20 + - ATR chip detects transaction on address 0x20, finds it in table, + propagates transaction on bus B with address translated to 0x10, + keeps clock streched on bus A waiting for reply + - Slave X chip (on bus B) detects transaction at its own physical + address 0x10 and replies normally + - ATR chip stops clock stretching and forwards reply on bus A, + with address translated back to 0x20 + - ATR driver receives the reply, rewrites messages with address 0x10 + as they were initially + - Slave X driver gets back the msgs[], with reply and address 0x10 + +Usage: + + 1. In the driver (typically in the probe function) add an ATR by + calling i2c_atr_new() passing attach/detach callbacks + 2. When the attach callback is called pick an appropriate alias, + configure it in the chip and return the chosen alias in the + alias_id parameter + 3. When the detach callback is called, deconfigure the alias from + the chip and put the alias back in the pool for later usage + +I2C ATR functions and data structures +------------------------------------- + +.. kernel-doc:: include/linux/i2c-atr.h diff --git a/Documentation/i2c/i2c-protocol.rst b/Documentation/i2c/i2c-protocol.rst new file mode 100644 index 0000000000..df0febfe64 --- /dev/null +++ b/Documentation/i2c/i2c-protocol.rst @@ -0,0 +1,96 @@ +================ +The I2C Protocol +================ + +This document is an overview of the basic I2C transactions and the kernel +APIs to perform them. + +Key to symbols +============== + +=============== ============================================================= +S Start condition +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded to + get a 10 bit I2C address. +Data (8 bits) A plain data byte. + +[..] Data sent by I2C device, as opposed to data sent by the + host adapter. +=============== ============================================================= + + +Simple send transaction +======================= + +Implemented by i2c_master_send():: + + S Addr Wr [A] Data [A] Data [A] ... [A] Data [A] P + + +Simple receive transaction +========================== + +Implemented by i2c_master_recv():: + + S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P + + +Combined transactions +===================== + +Implemented by i2c_transfer(). + +They are just like the above transactions, but instead of a stop +condition P a start condition S is sent and the transaction continues. +An example of a byte read, followed by a byte write:: + + S Addr Rd [A] [Data] NA S Addr Wr [A] Data [A] P + + +Modified transactions +===================== + +The following modifications to the I2C protocol can also be generated by +setting these flags for I2C messages. With the exception of I2C_M_NOSTART, they +are usually only needed to work around device issues: + +I2C_M_IGNORE_NAK: + Normally message is interrupted immediately if there is [NA] from the + client. Setting this flag treats any [NA] as [A], and all of + message is sent. + These messages may still fail to SCL lo->hi timeout. + +I2C_M_NO_RD_ACK: + In a read message, master A/NA bit is skipped. + +I2C_M_NOSTART: + In a combined transaction, no 'S Addr Wr/Rd [A]' is generated at some + point. For example, setting I2C_M_NOSTART on the second partial message + generates something like:: + + S Addr Rd [A] [Data] NA Data [A] P + + If you set the I2C_M_NOSTART variable for the first partial message, + we do not generate Addr, but we do generate the start condition S. + This will probably confuse all other clients on your bus, so don't + try this. + + This is often used to gather transmits from multiple data buffers in + system memory into something that appears as a single transfer to the + I2C device but may also be used between direction changes by some + rare devices. + +I2C_M_REV_DIR_ADDR: + This toggles the Rd/Wr flag. That is, if you want to do a write, but + need to emit an Rd instead of a Wr, or vice versa, you set this + flag. For example:: + + S Addr Rd [A] Data [A] Data [A] ... [A] Data [A] P + +I2C_M_STOP: + Force a stop condition (P) after the message. Some I2C related protocols + like SCCB require that. Normally, you really don't want to get interrupted + between the messages of one transfer. diff --git a/Documentation/i2c/i2c-stub.rst b/Documentation/i2c/i2c-stub.rst new file mode 100644 index 0000000000..a6fc6916d6 --- /dev/null +++ b/Documentation/i2c/i2c-stub.rst @@ -0,0 +1,66 @@ +======== +i2c-stub +======== + +Description +=========== + +This module is a very simple fake I2C/SMBus driver. It implements six +types of SMBus commands: write quick, (r/w) byte, (r/w) byte data, (r/w) +word data, (r/w) I2C block data, and (r/w) SMBus block data. + +You need to provide chip addresses as a module parameter when loading this +driver, which will then only react to SMBus commands to these addresses. + +No hardware is needed nor associated with this module. It will accept write +quick commands to the specified addresses; it will respond to the other +commands (also to the specified addresses) by reading from or writing to +arrays in memory. It will also spam the kernel logs for every command it +handles. + +A pointer register with auto-increment is implemented for all byte +operations. This allows for continuous byte reads like those supported by +EEPROMs, among others. + +SMBus block command support is disabled by default, and must be enabled +explicitly by setting the respective bits (0x03000000) in the functionality +module parameter. + +SMBus block commands must be written to configure an SMBus command for +SMBus block operations. Writes can be partial. Block read commands always +return the number of bytes selected with the largest write so far. + +The typical use-case is like this: + + 1. load this module + 2. use i2cset (from the i2c-tools project) to pre-load some data + 3. load the target chip driver module + 4. observe its behavior in the kernel log + +There's a script named i2c-stub-from-dump in the i2c-tools package which +can load register values automatically from a chip dump. + +Parameters +========== + +int chip_addr[10]: + The SMBus addresses to emulate chips at. + +unsigned long functionality: + Functionality override, to disable some commands. See I2C_FUNC_* + constants in <linux/i2c.h> for the suitable values. For example, + value 0x1f0000 would only enable the quick, byte and byte data + commands. + +u8 bank_reg[10], u8 bank_mask[10], u8 bank_start[10], u8 bank_end[10]: + Optional bank settings. They tell which bits in which register + select the active bank, as well as the range of banked registers. + +Caveats +======= + +If your target driver polls some byte or word waiting for it to change, the +stub could lock it up. Use i2cset to unlock it. + +If you spam it hard enough, printk can be lossy. This module really wants +something like relayfs. diff --git a/Documentation/i2c/i2c-sysfs.rst b/Documentation/i2c/i2c-sysfs.rst new file mode 100644 index 0000000000..78c54c658f --- /dev/null +++ b/Documentation/i2c/i2c-sysfs.rst @@ -0,0 +1,387 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============== +Linux I2C Sysfs +=============== + +Overview +======== + +I2C topology can be complex because of the existence of I2C MUX +(I2C Multiplexer). The Linux +kernel abstracts the MUX channels into logical I2C bus numbers. However, there +is a gap of knowledge to map from the I2C bus physical number and MUX topology +to logical I2C bus number. This doc is aimed to fill in this gap, so the +audience (hardware engineers and new software developers for example) can learn +the concept of logical I2C buses in the kernel, by knowing the physical I2C +topology and navigating through the I2C sysfs in Linux shell. This knowledge is +useful and essential to use ``i2c-tools`` for the purpose of development and +debugging. + +Target audience +--------------- + +People who need to use Linux shell to interact with I2C subsystem on a system +which the Linux is running on. + +Prerequisites +------------- + +1. Knowledge of general Linux shell file system commands and operations. + +2. General knowledge of I2C, I2C MUX and I2C topology. + +Location of I2C Sysfs +===================== + +Typically, the Linux Sysfs filesystem is mounted at the ``/sys`` directory, +so you can find the I2C Sysfs under ``/sys/bus/i2c/devices`` +where you can directly ``cd`` to it. +There is a list of symbolic links under that directory. The links that +start with ``i2c-`` are I2C buses, which may be either physical or logical. The +other links that begin with numbers and end with numbers are I2C devices, where +the first number is I2C bus number, and the second number is I2C address. + +Google Pixel 3 phone for example:: + + blueline:/sys/bus/i2c/devices $ ls + 0-0008 0-0061 1-0028 3-0043 4-0036 4-0041 i2c-1 i2c-3 + 0-000c 0-0066 2-0049 4-000b 4-0040 i2c-0 i2c-2 i2c-4 + +``i2c-2`` is an I2C bus whose number is 2, and ``2-0049`` is an I2C device +on bus 2 address 0x49 bound with a kernel driver. + +Terminology +=========== + +First, let us define some terms to avoid confusion in later sections. + +(Physical) I2C Bus Controller +----------------------------- + +The hardware system that the Linux kernel is running on may have multiple +physical I2C bus controllers. The controllers are hardware and physical, and the +system may define multiple registers in the memory space to manipulate the +controllers. Linux kernel has I2C bus drivers under source directory +``drivers/i2c/busses`` to translate kernel I2C API into register +operations for different systems. This terminology is not limited to Linux +kernel only. + +I2C Bus Physical Number +----------------------- + +For each physical I2C bus controller, the system vendor may assign a physical +number to each controller. For example, the first I2C bus controller which has +the lowest register addresses may be called ``I2C-0``. + +Logical I2C Bus +--------------- + +Every I2C bus number you see in Linux I2C Sysfs is a logical I2C bus with a +number assigned. This is similar to the fact that software code is usually +written upon virtual memory space, instead of physical memory space. + +Each logical I2C bus may be an abstraction of a physical I2C bus controller, or +an abstraction of a channel behind an I2C MUX. In case it is an abstraction of a +MUX channel, whenever we access an I2C device via a such logical bus, the kernel +will switch the I2C MUX for you to the proper channel as part of the +abstraction. + +Physical I2C Bus +---------------- + +If the logical I2C bus is a direct abstraction of a physical I2C bus controller, +let us call it a physical I2C bus. + +Caveat +------ + +This may be a confusing part for people who only know about the physical I2C +design of a board. It is actually possible to rename the I2C bus physical number +to a different number in logical I2C bus level in Device Tree Source (DTS) under +section ``aliases``. See ``arch/arm/boot/dts/nuvoton-npcm730-gsj.dts`` +for an example of DTS file. + +Best Practice: **(To kernel software developers)** It is better to keep the I2C +bus physical number the same as their corresponding logical I2C bus number, +instead of renaming or mapping them, so that it may be less confusing to other +users. These physical I2C buses can be served as good starting points for I2C +MUX fanouts. For the following examples, we will assume that the physical I2C +bus has a number same as their I2C bus physical number. + +Walk through Logical I2C Bus +============================ + +For the following content, we will use a more complex I2C topology as an +example. Here is a brief graph for the I2C topology. If you do not understand +this graph at first glance, do not be afraid to continue reading this doc +and review it when you finish reading. + +:: + + i2c-7 (physical I2C bus controller 7) + `-- 7-0071 (4-channel I2C MUX at 0x71) + |-- i2c-60 (channel-0) + |-- i2c-73 (channel-1) + | |-- 73-0040 (I2C sensor device with hwmon directory) + | |-- 73-0070 (I2C MUX at 0x70, exists in DTS, but failed to probe) + | `-- 73-0072 (8-channel I2C MUX at 0x72) + | |-- i2c-78 (channel-0) + | |-- ... (channel-1...6, i2c-79...i2c-84) + | `-- i2c-85 (channel-7) + |-- i2c-86 (channel-2) + `-- i2c-203 (channel-3) + +Distinguish Physical and Logical I2C Bus +---------------------------------------- + +One simple way to distinguish between a physical I2C bus and a logical I2C bus, +is to read the symbolic link ``device`` under the I2C bus directory by using +command ``ls -l`` or ``readlink``. + +An alternative symbolic link to check is ``mux_device``. This link only exists +in logical I2C bus directory which is fanned out from another I2C bus. +Reading this link will also tell you which I2C MUX device created +this logical I2C bus. + +If the symbolic link points to a directory ending with ``.i2c``, it should be a +physical I2C bus, directly abstracting a physical I2C bus controller. For +example:: + + $ readlink /sys/bus/i2c/devices/i2c-7/device + ../../f0087000.i2c + $ ls /sys/bus/i2c/devices/i2c-7/mux_device + ls: /sys/bus/i2c/devices/i2c-7/mux_device: No such file or directory + +In this case, ``i2c-7`` is a physical I2C bus, so it does not have the symbolic +link ``mux_device`` under its directory. And if the kernel software developer +follows the common practice by not renaming physical I2C buses, this should also +mean the physical I2C bus controller 7 of the system. + +On the other hand, if the symbolic link points to another I2C bus, the I2C bus +presented by the current directory has to be a logical bus. The I2C bus pointed +by the link is the parent bus which may be either a physical I2C bus or a +logical one. In this case, the I2C bus presented by the current directory +abstracts an I2C MUX channel under the parent bus. + +For example:: + + $ readlink /sys/bus/i2c/devices/i2c-73/device + ../../i2c-7 + $ readlink /sys/bus/i2c/devices/i2c-73/mux_device + ../7-0071 + +``i2c-73`` is a logical bus fanout by an I2C MUX under ``i2c-7`` +whose I2C address is 0x71. +Whenever we access an I2C device with bus 73, the kernel will always +switch the I2C MUX addressed 0x71 to the proper channel for you as part of the +abstraction. + +Finding out Logical I2C Bus Number +---------------------------------- + +In this section, we will describe how to find out the logical I2C bus number +representing certain I2C MUX channels based on the knowledge of physical +hardware I2C topology. + +In this example, we have a system which has a physical I2C bus 7 and not renamed +in DTS. There is a 4-channel MUX at address 0x71 on that bus. There is another +8-channel MUX at address 0x72 behind the channel 1 of the 0x71 MUX. Let us +navigate through Sysfs and find out the logical I2C bus number of the channel 3 +of the 0x72 MUX. + +First of all, let us go to the directory of ``i2c-7``:: + + ~$ cd /sys/bus/i2c/devices/i2c-7 + /sys/bus/i2c/devices/i2c-7$ ls + 7-0071 i2c-60 name subsystem + delete_device i2c-73 new_device uevent + device i2c-86 of_node + i2c-203 i2c-dev power + +There, we see the 0x71 MUX as ``7-0071``. Go inside it:: + + /sys/bus/i2c/devices/i2c-7$ cd 7-0071/ + /sys/bus/i2c/devices/i2c-7/7-0071$ ls -l + channel-0 channel-3 modalias power + channel-1 driver name subsystem + channel-2 idle_state of_node uevent + +Read the link ``channel-1`` using ``readlink`` or ``ls -l``:: + + /sys/bus/i2c/devices/i2c-7/7-0071$ readlink channel-1 + ../i2c-73 + +We find out that the channel 1 of 0x71 MUX on ``i2c-7`` is assigned +with a logical I2C bus number of 73. +Let us continue the journey to directory ``i2c-73`` in either ways:: + + # cd to i2c-73 under I2C Sysfs root + /sys/bus/i2c/devices/i2c-7/7-0071$ cd /sys/bus/i2c/devices/i2c-73 + /sys/bus/i2c/devices/i2c-73$ + + # cd the channel symbolic link + /sys/bus/i2c/devices/i2c-7/7-0071$ cd channel-1 + /sys/bus/i2c/devices/i2c-7/7-0071/channel-1$ + + # cd the link content + /sys/bus/i2c/devices/i2c-7/7-0071$ cd ../i2c-73 + /sys/bus/i2c/devices/i2c-7/i2c-73$ + +Either ways, you will end up in the directory of ``i2c-73``. Similar to above, +we can now find the 0x72 MUX and what logical I2C bus numbers +that its channels are assigned:: + + /sys/bus/i2c/devices/i2c-73$ ls + 73-0040 device i2c-83 new_device + 73-004e i2c-78 i2c-84 of_node + 73-0050 i2c-79 i2c-85 power + 73-0070 i2c-80 i2c-dev subsystem + 73-0072 i2c-81 mux_device uevent + delete_device i2c-82 name + /sys/bus/i2c/devices/i2c-73$ cd 73-0072 + /sys/bus/i2c/devices/i2c-73/73-0072$ ls + channel-0 channel-4 driver of_node + channel-1 channel-5 idle_state power + channel-2 channel-6 modalias subsystem + channel-3 channel-7 name uevent + /sys/bus/i2c/devices/i2c-73/73-0072$ readlink channel-3 + ../i2c-81 + +There, we find out the logical I2C bus number of the channel 3 of the 0x72 MUX +is 81. We can later use this number to switch to its own I2C Sysfs directory or +issue ``i2c-tools`` commands. + +Tip: Once you understand the I2C topology with MUX, command +`i2cdetect -l +<https://manpages.debian.org/unstable/i2c-tools/i2cdetect.8.en.html>`_ +in +`I2C Tools +<https://i2c.wiki.kernel.org/index.php/I2C_Tools>`_ +can give you +an overview of the I2C topology easily, if it is available on your system. For +example:: + + $ i2cdetect -l | grep -e '\-73' -e _7 | sort -V + i2c-7 i2c npcm_i2c_7 I2C adapter + i2c-73 i2c i2c-7-mux (chan_id 1) I2C adapter + i2c-78 i2c i2c-73-mux (chan_id 0) I2C adapter + i2c-79 i2c i2c-73-mux (chan_id 1) I2C adapter + i2c-80 i2c i2c-73-mux (chan_id 2) I2C adapter + i2c-81 i2c i2c-73-mux (chan_id 3) I2C adapter + i2c-82 i2c i2c-73-mux (chan_id 4) I2C adapter + i2c-83 i2c i2c-73-mux (chan_id 5) I2C adapter + i2c-84 i2c i2c-73-mux (chan_id 6) I2C adapter + i2c-85 i2c i2c-73-mux (chan_id 7) I2C adapter + +Pinned Logical I2C Bus Number +----------------------------- + +If not specified in DTS, when an I2C MUX driver is applied and the MUX device is +successfully probed, the kernel will assign the MUX channels with a logical bus +number based on the current biggest logical bus number incrementally. For +example, if the system has ``i2c-15`` as the highest logical bus number, and a +4-channel MUX is applied successfully, we will have ``i2c-16`` for the +MUX channel 0, and all the way to ``i2c-19`` for the MUX channel 3. + +The kernel software developer is able to pin the fanout MUX channels to a static +logical I2C bus number in the DTS. This doc will not go through the details on +how to implement this in DTS, but we can see an example in: +``arch/arm/boot/dts/aspeed-bmc-facebook-wedge400.dts`` + +In the above example, there is an 8-channel I2C MUX at address 0x70 on physical +I2C bus 2. The channel 2 of the MUX is defined as ``imux18`` in DTS, +and pinned to logical I2C bus number 18 with the line of ``i2c18 = &imux18;`` +in section ``aliases``. + +Take it further, it is possible to design a logical I2C bus number schema that +can be easily remembered by humans or calculated arithmetically. For example, we +can pin the fanout channels of a MUX on bus 3 to start at 30. So 30 will be the +logical bus number of the channel 0 of the MUX on bus 3, and 37 will be the +logical bus number of the channel 7 of the MUX on bus 3. + +I2C Devices +=========== + +In previous sections, we mostly covered the I2C bus. In this section, let us see +what we can learn from the I2C device directory whose link name is in the format +of ``${bus}-${addr}``. The ``${bus}`` part in the name is a logical I2C bus +decimal number, while the ``${addr}`` part is a hex number of the I2C address +of each device. + +I2C Device Directory Content +---------------------------- + +Inside each I2C device directory, there is a file named ``name``. +This file tells what device name it was used for the kernel driver to +probe this device. Use command ``cat`` to read its content. For example:: + + /sys/bus/i2c/devices/i2c-73$ cat 73-0040/name + ina230 + /sys/bus/i2c/devices/i2c-73$ cat 73-0070/name + pca9546 + /sys/bus/i2c/devices/i2c-73$ cat 73-0072/name + pca9547 + +There is a symbolic link named ``driver`` to tell what Linux kernel driver was +used to probe this device:: + + /sys/bus/i2c/devices/i2c-73$ readlink -f 73-0040/driver + /sys/bus/i2c/drivers/ina2xx + /sys/bus/i2c/devices/i2c-73$ readlink -f 73-0072/driver + /sys/bus/i2c/drivers/pca954x + +But if the link ``driver`` does not exist at the first place, +it may mean that the kernel driver failed to probe this device due to +some errors. The error may be found in ``dmesg``:: + + /sys/bus/i2c/devices/i2c-73$ ls 73-0070/driver + ls: 73-0070/driver: No such file or directory + /sys/bus/i2c/devices/i2c-73$ dmesg | grep 73-0070 + pca954x 73-0070: probe failed + pca954x 73-0070: probe failed + +Depending on what the I2C device is and what kernel driver was used to probe the +device, we may have different content in the device directory. + +I2C MUX Device +-------------- + +While you may be already aware of this in previous sections, an I2C MUX device +will have symbolic link ``channel-*`` inside its device directory. +These symbolic links point to their logical I2C bus directories:: + + /sys/bus/i2c/devices/i2c-73$ ls -l 73-0072/channel-* + lrwxrwxrwx ... 73-0072/channel-0 -> ../i2c-78 + lrwxrwxrwx ... 73-0072/channel-1 -> ../i2c-79 + lrwxrwxrwx ... 73-0072/channel-2 -> ../i2c-80 + lrwxrwxrwx ... 73-0072/channel-3 -> ../i2c-81 + lrwxrwxrwx ... 73-0072/channel-4 -> ../i2c-82 + lrwxrwxrwx ... 73-0072/channel-5 -> ../i2c-83 + lrwxrwxrwx ... 73-0072/channel-6 -> ../i2c-84 + lrwxrwxrwx ... 73-0072/channel-7 -> ../i2c-85 + +I2C Sensor Device / Hwmon +------------------------- + +I2C sensor device is also common to see. If they are bound by a kernel hwmon +(Hardware Monitoring) driver successfully, you will see a ``hwmon`` directory +inside the I2C device directory. Keep digging into it, you will find the Hwmon +Sysfs for the I2C sensor device:: + + /sys/bus/i2c/devices/i2c-73/73-0040/hwmon/hwmon17$ ls + curr1_input in0_lcrit_alarm name subsystem + device in1_crit power uevent + in0_crit in1_crit_alarm power1_crit update_interval + in0_crit_alarm in1_input power1_crit_alarm + in0_input in1_lcrit power1_input + in0_lcrit in1_lcrit_alarm shunt_resistor + +For more info on the Hwmon Sysfs, refer to the doc: + +../hwmon/sysfs-interface.rst + +Instantiate I2C Devices in I2C Sysfs +------------------------------------ + +Refer to section "Method 4: Instantiate from user-space" of instantiating-devices.rst diff --git a/Documentation/i2c/i2c-topology.rst b/Documentation/i2c/i2c-topology.rst new file mode 100644 index 0000000000..48fce0f749 --- /dev/null +++ b/Documentation/i2c/i2c-topology.rst @@ -0,0 +1,412 @@ +================================ +I2C muxes and complex topologies +================================ + +There are a couple of reasons for building more complex I2C topologies +than a straight-forward I2C bus with one adapter and one or more devices. + +Some example use cases are: + +1. A mux may be needed on the bus to prevent address collisions. + +2. The bus may be accessible from some external bus master, and arbitration + may be needed to determine if it is ok to access the bus. + +3. A device (particularly RF tuners) may want to avoid the digital noise + from the I2C bus, at least most of the time, and sits behind a gate + that has to be operated before the device can be accessed. + +Several types of hardware components such as I2C muxes, I2C gates and I2C +arbitrators allow to handle such needs. + +These components are represented as I2C adapter trees by Linux, where +each adapter has a parent adapter (except the root adapter) and zero or +more child adapters. The root adapter is the actual adapter that issues +I2C transfers, and all adapters with a parent are part of an "i2c-mux" +object (quoted, since it can also be an arbitrator or a gate). + +Depending of the particular mux driver, something happens when there is +an I2C transfer on one of its child adapters. The mux driver can +obviously operate a mux, but it can also do arbitration with an external +bus master or open a gate. The mux driver has two operations for this, +select and deselect. select is called before the transfer and (the +optional) deselect is called after the transfer. + + +Locking +======= + +There are two variants of locking available to I2C muxes, they can be +mux-locked or parent-locked muxes. + + +Mux-locked muxes +---------------- + +Mux-locked muxes does not lock the entire parent adapter during the +full select-transfer-deselect transaction, only the muxes on the parent +adapter are locked. Mux-locked muxes are mostly interesting if the +select and/or deselect operations must use I2C transfers to complete +their tasks. Since the parent adapter is not fully locked during the +full transaction, unrelated I2C transfers may interleave the different +stages of the transaction. This has the benefit that the mux driver +may be easier and cleaner to implement, but it has some caveats. + +Mux-locked Example +~~~~~~~~~~~~~~~~~~ + +:: + + .----------. .--------. + .--------. | mux- |-----| dev D1 | + | root |--+--| locked | '--------' + '--------' | | mux M1 |--. .--------. + | '----------' '--| dev D2 | + | .--------. '--------' + '--| dev D3 | + '--------' + +When there is an access to D1, this happens: + + 1. Someone issues an I2C transfer to D1. + 2. M1 locks muxes on its parent (the root adapter in this case). + 3. M1 calls ->select to ready the mux. + 4. M1 (presumably) does some I2C transfers as part of its select. + These transfers are normal I2C transfers that locks the parent + adapter. + 5. M1 feeds the I2C transfer from step 1 to its parent adapter as a + normal I2C transfer that locks the parent adapter. + 6. M1 calls ->deselect, if it has one. + 7. Same rules as in step 4, but for ->deselect. + 8. M1 unlocks muxes on its parent. + +This means that accesses to D2 are lockout out for the full duration +of the entire operation. But accesses to D3 are possibly interleaved +at any point. + +Mux-locked caveats +~~~~~~~~~~~~~~~~~~ + +When using a mux-locked mux, be aware of the following restrictions: + +[ML1] + If you build a topology with a mux-locked mux being the parent + of a parent-locked mux, this might break the expectation from the + parent-locked mux that the root adapter is locked during the + transaction. + +[ML2] + It is not safe to build arbitrary topologies with two (or more) + mux-locked muxes that are not siblings, when there are address + collisions between the devices on the child adapters of these + non-sibling muxes. + + I.e. the select-transfer-deselect transaction targeting e.g. device + address 0x42 behind mux-one may be interleaved with a similar + operation targeting device address 0x42 behind mux-two. The + intent with such a topology would in this hypothetical example + be that mux-one and mux-two should not be selected simultaneously, + but mux-locked muxes do not guarantee that in all topologies. + +[ML3] + A mux-locked mux cannot be used by a driver for auto-closing + gates/muxes, i.e. something that closes automatically after a given + number (one, in most cases) of I2C transfers. Unrelated I2C transfers + may creep in and close prematurely. + +[ML4] + If any non-I2C operation in the mux driver changes the I2C mux state, + the driver has to lock the root adapter during that operation. + Otherwise garbage may appear on the bus as seen from devices + behind the mux, when an unrelated I2C transfer is in flight during + the non-I2C mux-changing operation. + + +Parent-locked muxes +------------------- + +Parent-locked muxes lock the parent adapter during the full select- +transfer-deselect transaction. The implication is that the mux driver +has to ensure that any and all I2C transfers through that parent +adapter during the transaction are unlocked I2C transfers (using e.g. +__i2c_transfer), or a deadlock will follow. + +Parent-locked Example +~~~~~~~~~~~~~~~~~~~~~ + +:: + + .----------. .--------. + .--------. | parent- |-----| dev D1 | + | root |--+--| locked | '--------' + '--------' | | mux M1 |--. .--------. + | '----------' '--| dev D2 | + | .--------. '--------' + '--| dev D3 | + '--------' + +When there is an access to D1, this happens: + + 1. Someone issues an I2C transfer to D1. + 2. M1 locks muxes on its parent (the root adapter in this case). + 3. M1 locks its parent adapter. + 4. M1 calls ->select to ready the mux. + 5. If M1 does any I2C transfers (on this root adapter) as part of + its select, those transfers must be unlocked I2C transfers so + that they do not deadlock the root adapter. + 6. M1 feeds the I2C transfer from step 1 to the root adapter as an + unlocked I2C transfer, so that it does not deadlock the parent + adapter. + 7. M1 calls ->deselect, if it has one. + 8. Same rules as in step 5, but for ->deselect. + 9. M1 unlocks its parent adapter. + 10. M1 unlocks muxes on its parent. + +This means that accesses to both D2 and D3 are locked out for the full +duration of the entire operation. + +Parent-locked Caveats +~~~~~~~~~~~~~~~~~~~~~ + +When using a parent-locked mux, be aware of the following restrictions: + +[PL1] + If you build a topology with a parent-locked mux being the child + of another mux, this might break a possible assumption from the + child mux that the root adapter is unused between its select op + and the actual transfer (e.g. if the child mux is auto-closing + and the parent mux issues I2C transfers as part of its select). + This is especially the case if the parent mux is mux-locked, but + it may also happen if the parent mux is parent-locked. + +[PL2] + If select/deselect calls out to other subsystems such as gpio, + pinctrl, regmap or iio, it is essential that any I2C transfers + caused by these subsystems are unlocked. This can be convoluted to + accomplish, maybe even impossible if an acceptably clean solution + is sought. + + +Complex Examples +================ + +Parent-locked mux as parent of parent-locked mux +------------------------------------------------ + +This is a useful topology, but it can be bad:: + + .----------. .----------. .--------. + .--------. | parent- |-----| parent- |-----| dev D1 | + | root |--+--| locked | | locked | '--------' + '--------' | | mux M1 |--. | mux M2 |--. .--------. + | '----------' | '----------' '--| dev D2 | + | .--------. | .--------. '--------' + '--| dev D4 | '--| dev D3 | + '--------' '--------' + +When any device is accessed, all other devices are locked out for +the full duration of the operation (both muxes lock their parent, +and specifically when M2 requests its parent to lock, M1 passes +the buck to the root adapter). + +This topology is bad if M2 is an auto-closing mux and M1->select +issues any unlocked I2C transfers on the root adapter that may leak +through and be seen by the M2 adapter, thus closing M2 prematurely. + + +Mux-locked mux as parent of mux-locked mux +------------------------------------------ + +This is a good topology:: + + .----------. .----------. .--------. + .--------. | mux- |-----| mux- |-----| dev D1 | + | root |--+--| locked | | locked | '--------' + '--------' | | mux M1 |--. | mux M2 |--. .--------. + | '----------' | '----------' '--| dev D2 | + | .--------. | .--------. '--------' + '--| dev D4 | '--| dev D3 | + '--------' '--------' + +When device D1 is accessed, accesses to D2 are locked out for the +full duration of the operation (muxes on the top child adapter of M1 +are locked). But accesses to D3 and D4 are possibly interleaved at +any point. + +Accesses to D3 locks out D1 and D2, but accesses to D4 are still possibly +interleaved. + + +Mux-locked mux as parent of parent-locked mux +--------------------------------------------- + +This is probably a bad topology:: + + .----------. .----------. .--------. + .--------. | mux- |-----| parent- |-----| dev D1 | + | root |--+--| locked | | locked | '--------' + '--------' | | mux M1 |--. | mux M2 |--. .--------. + | '----------' | '----------' '--| dev D2 | + | .--------. | .--------. '--------' + '--| dev D4 | '--| dev D3 | + '--------' '--------' + +When device D1 is accessed, accesses to D2 and D3 are locked out +for the full duration of the operation (M1 locks child muxes on the +root adapter). But accesses to D4 are possibly interleaved at any +point. + +This kind of topology is generally not suitable and should probably +be avoided. The reason is that M2 probably assumes that there will +be no I2C transfers during its calls to ->select and ->deselect, and +if there are, any such transfers might appear on the slave side of M2 +as partial I2C transfers, i.e. garbage or worse. This might cause +device lockups and/or other problems. + +The topology is especially troublesome if M2 is an auto-closing +mux. In that case, any interleaved accesses to D4 might close M2 +prematurely, as might any I2C transfers part of M1->select. + +But if M2 is not making the above stated assumption, and if M2 is not +auto-closing, the topology is fine. + + +Parent-locked mux as parent of mux-locked mux +--------------------------------------------- + +This is a good topology:: + + .----------. .----------. .--------. + .--------. | parent- |-----| mux- |-----| dev D1 | + | root |--+--| locked | | locked | '--------' + '--------' | | mux M1 |--. | mux M2 |--. .--------. + | '----------' | '----------' '--| dev D2 | + | .--------. | .--------. '--------' + '--| dev D4 | '--| dev D3 | + '--------' '--------' + +When D1 is accessed, accesses to D2 are locked out for the full +duration of the operation (muxes on the top child adapter of M1 +are locked). Accesses to D3 and D4 are possibly interleaved at +any point, just as is expected for mux-locked muxes. + +When D3 or D4 are accessed, everything else is locked out. For D3 +accesses, M1 locks the root adapter. For D4 accesses, the root +adapter is locked directly. + + +Two mux-locked sibling muxes +---------------------------- + +This is a good topology:: + + .--------. + .----------. .--| dev D1 | + | mux- |--' '--------' + .--| locked | .--------. + | | mux M1 |-----| dev D2 | + | '----------' '--------' + | .----------. .--------. + .--------. | | mux- |-----| dev D3 | + | root |--+--| locked | '--------' + '--------' | | mux M2 |--. .--------. + | '----------' '--| dev D4 | + | .--------. '--------' + '--| dev D5 | + '--------' + +When D1 is accessed, accesses to D2, D3 and D4 are locked out. But +accesses to D5 may be interleaved at any time. + + +Two parent-locked sibling muxes +------------------------------- + +This is a good topology:: + + .--------. + .----------. .--| dev D1 | + | parent- |--' '--------' + .--| locked | .--------. + | | mux M1 |-----| dev D2 | + | '----------' '--------' + | .----------. .--------. + .--------. | | parent- |-----| dev D3 | + | root |--+--| locked | '--------' + '--------' | | mux M2 |--. .--------. + | '----------' '--| dev D4 | + | .--------. '--------' + '--| dev D5 | + '--------' + +When any device is accessed, accesses to all other devices are locked +out. + + +Mux-locked and parent-locked sibling muxes +------------------------------------------ + +This is a good topology:: + + .--------. + .----------. .--| dev D1 | + | mux- |--' '--------' + .--| locked | .--------. + | | mux M1 |-----| dev D2 | + | '----------' '--------' + | .----------. .--------. + .--------. | | parent- |-----| dev D3 | + | root |--+--| locked | '--------' + '--------' | | mux M2 |--. .--------. + | '----------' '--| dev D4 | + | .--------. '--------' + '--| dev D5 | + '--------' + +When D1 or D2 are accessed, accesses to D3 and D4 are locked out while +accesses to D5 may interleave. When D3 or D4 are accessed, accesses to +all other devices are locked out. + + +Mux type of existing device drivers +=================================== + +Whether a device is mux-locked or parent-locked depends on its +implementation. The following list was correct at the time of writing: + +In drivers/i2c/muxes/: + +====================== ============================================= +i2c-arb-gpio-challenge Parent-locked +i2c-mux-gpio Normally parent-locked, mux-locked iff + all involved gpio pins are controlled by the + same I2C root adapter that they mux. +i2c-mux-gpmux Normally parent-locked, mux-locked iff + specified in device-tree. +i2c-mux-ltc4306 Mux-locked +i2c-mux-mlxcpld Parent-locked +i2c-mux-pca9541 Parent-locked +i2c-mux-pca954x Parent-locked +i2c-mux-pinctrl Normally parent-locked, mux-locked iff + all involved pinctrl devices are controlled + by the same I2C root adapter that they mux. +i2c-mux-reg Parent-locked +====================== ============================================= + +In drivers/iio/: + +====================== ============================================= +gyro/mpu3050 Mux-locked +imu/inv_mpu6050/ Mux-locked +====================== ============================================= + +In drivers/media/: + +======================= ============================================= +dvb-frontends/lgdt3306a Mux-locked +dvb-frontends/m88ds3103 Parent-locked +dvb-frontends/rtl2830 Parent-locked +dvb-frontends/rtl2832 Mux-locked +dvb-frontends/si2168 Mux-locked +usb/cx231xx/ Parent-locked +======================= ============================================= diff --git a/Documentation/i2c/i2c_bus.svg b/Documentation/i2c/i2c_bus.svg new file mode 100644 index 0000000000..3170de9763 --- /dev/null +++ b/Documentation/i2c/i2c_bus.svg @@ -0,0 +1,1341 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!-- Created with Inkscape (http://www.inkscape.org/) --> + +<svg + xmlns:dc="http://purl.org/dc/elements/1.1/" + xmlns:cc="http://creativecommons.org/ns#" + xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" + xmlns:svg="http://www.w3.org/2000/svg" + xmlns="http://www.w3.org/2000/svg" + xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd" + 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SPDX-License-Identifier: GPL-2.0 + +=================== +I2C/SMBus Subsystem +=================== + +Introduction +============ + +.. toctree:: + :maxdepth: 1 + + summary + i2c-protocol + smbus-protocol + instantiating-devices + busses/index + i2c-topology + muxes/i2c-mux-gpio + i2c-sysfs + i2c-address-translators + +Writing device drivers +====================== + +.. toctree:: + :maxdepth: 1 + + writing-clients + dev-interface + dma-considerations + fault-codes + functionality + +Debugging +========= + +.. toctree:: + :maxdepth: 1 + + gpio-fault-injection + i2c-stub + +Slave I2C +========= + +.. toctree:: + :maxdepth: 1 + + slave-interface + slave-eeprom-backend + slave-testunit-backend + +Advanced topics +=============== + +.. toctree:: + :maxdepth: 1 + + ten-bit-addresses + +Legacy documentation +==================== + +.. toctree:: + :maxdepth: 1 + + old-module-parameters + +.. only:: subproject and html + + Indices + ======= + + * :ref:`genindex` diff --git a/Documentation/i2c/instantiating-devices.rst b/Documentation/i2c/instantiating-devices.rst new file mode 100644 index 0000000000..3ea056a958 --- /dev/null +++ b/Documentation/i2c/instantiating-devices.rst @@ -0,0 +1,272 @@ +============================== +How to instantiate I2C devices +============================== + +Unlike PCI or USB devices, I2C devices are not enumerated at the hardware +level. Instead, the software must know which devices are connected on each +I2C bus segment, and what address these devices are using. For this +reason, the kernel code must instantiate I2C devices explicitly. There are +several ways to achieve this, depending on the context and requirements. + + +Method 1: Declare the I2C devices statically +-------------------------------------------- + +This method is appropriate when the I2C bus is a system bus as is the case +for many embedded systems. On such systems, each I2C bus has a number which +is known in advance. It is thus possible to pre-declare the I2C devices +which live on this bus. + +This information is provided to the kernel in a different way on different +architectures: device tree, ACPI or board files. + +When the I2C bus in question is registered, the I2C devices will be +instantiated automatically by i2c-core. The devices will be automatically +unbound and destroyed when the I2C bus they sit on goes away (if ever). + + +Declare the I2C devices via devicetree +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +On platforms using devicetree, the declaration of I2C devices is done in +subnodes of the master controller. + +Example: + +.. code-block:: dts + + i2c1: i2c@400a0000 { + /* ... master properties skipped ... */ + clock-frequency = <100000>; + + flash@50 { + compatible = "atmel,24c256"; + reg = <0x50>; + }; + + pca9532: gpio@60 { + compatible = "nxp,pca9532"; + gpio-controller; + #gpio-cells = <2>; + reg = <0x60>; + }; + }; + +Here, two devices are attached to the bus using a speed of 100kHz. For +additional properties which might be needed to set up the device, please refer +to its devicetree documentation in Documentation/devicetree/bindings/. + + +Declare the I2C devices via ACPI +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +ACPI can also describe I2C devices. There is special documentation for this +which is currently located at Documentation/firmware-guide/acpi/enumeration.rst. + + +Declare the I2C devices in board files +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +In many embedded architectures, devicetree has replaced the old hardware +description based on board files, but the latter are still used in old +code. Instantiating I2C devices via board files is done with an array of +struct i2c_board_info which is registered by calling +i2c_register_board_info(). + +Example (from omap2 h4): + +.. code-block:: c + + static struct i2c_board_info h4_i2c_board_info[] __initdata = { + { + I2C_BOARD_INFO("isp1301_omap", 0x2d), + .irq = OMAP_GPIO_IRQ(125), + }, + { /* EEPROM on mainboard */ + I2C_BOARD_INFO("24c01", 0x52), + .platform_data = &m24c01, + }, + { /* EEPROM on cpu card */ + I2C_BOARD_INFO("24c01", 0x57), + .platform_data = &m24c01, + }, + }; + + static void __init omap_h4_init(void) + { + (...) + i2c_register_board_info(1, h4_i2c_board_info, + ARRAY_SIZE(h4_i2c_board_info)); + (...) + } + +The above code declares 3 devices on I2C bus 1, including their respective +addresses and custom data needed by their drivers. + + +Method 2: Instantiate the devices explicitly +-------------------------------------------- + +This method is appropriate when a larger device uses an I2C bus for +internal communication. A typical case is TV adapters. These can have a +tuner, a video decoder, an audio decoder, etc. usually connected to the +main chip by the means of an I2C bus. You won't know the number of the I2C +bus in advance, so the method 1 described above can't be used. Instead, +you can instantiate your I2C devices explicitly. This is done by filling +a struct i2c_board_info and calling i2c_new_client_device(). + +Example (from the sfe4001 network driver): + +.. code-block:: c + + static struct i2c_board_info sfe4001_hwmon_info = { + I2C_BOARD_INFO("max6647", 0x4e), + }; + + int sfe4001_init(struct efx_nic *efx) + { + (...) + efx->board_info.hwmon_client = + i2c_new_client_device(&efx->i2c_adap, &sfe4001_hwmon_info); + + (...) + } + +The above code instantiates 1 I2C device on the I2C bus which is on the +network adapter in question. + +A variant of this is when you don't know for sure if an I2C device is +present or not (for example for an optional feature which is not present +on cheap variants of a board but you have no way to tell them apart), or +it may have different addresses from one board to the next (manufacturer +changing its design without notice). In this case, you can call +i2c_new_scanned_device() instead of i2c_new_client_device(). + +Example (from the nxp OHCI driver): + +.. code-block:: c + + static const unsigned short normal_i2c[] = { 0x2c, 0x2d, I2C_CLIENT_END }; + + static int usb_hcd_nxp_probe(struct platform_device *pdev) + { + (...) + struct i2c_adapter *i2c_adap; + struct i2c_board_info i2c_info; + + (...) + i2c_adap = i2c_get_adapter(2); + memset(&i2c_info, 0, sizeof(struct i2c_board_info)); + strscpy(i2c_info.type, "isp1301_nxp", sizeof(i2c_info.type)); + isp1301_i2c_client = i2c_new_scanned_device(i2c_adap, &i2c_info, + normal_i2c, NULL); + i2c_put_adapter(i2c_adap); + (...) + } + +The above code instantiates up to 1 I2C device on the I2C bus which is on +the OHCI adapter in question. It first tries at address 0x2c, if nothing +is found there it tries address 0x2d, and if still nothing is found, it +simply gives up. + +The driver which instantiated the I2C device is responsible for destroying +it on cleanup. This is done by calling i2c_unregister_device() on the +pointer that was earlier returned by i2c_new_client_device() or +i2c_new_scanned_device(). + + +Method 3: Probe an I2C bus for certain devices +---------------------------------------------- + +Sometimes you do not have enough information about an I2C device, not even +to call i2c_new_scanned_device(). The typical case is hardware monitoring +chips on PC mainboards. There are several dozen models, which can live +at 25 different addresses. Given the huge number of mainboards out there, +it is next to impossible to build an exhaustive list of the hardware +monitoring chips being used. Fortunately, most of these chips have +manufacturer and device ID registers, so they can be identified by +probing. + +In that case, I2C devices are neither declared nor instantiated +explicitly. Instead, i2c-core will probe for such devices as soon as their +drivers are loaded, and if any is found, an I2C device will be +instantiated automatically. In order to prevent any misbehavior of this +mechanism, the following restrictions apply: + +* The I2C device driver must implement the detect() method, which + identifies a supported device by reading from arbitrary registers. +* Only buses which are likely to have a supported device and agree to be + probed, will be probed. For example this avoids probing for hardware + monitoring chips on a TV adapter. + +Example: +See lm90_driver and lm90_detect() in drivers/hwmon/lm90.c + +I2C devices instantiated as a result of such a successful probe will be +destroyed automatically when the driver which detected them is removed, +or when the underlying I2C bus is itself destroyed, whichever happens +first. + +Those of you familiar with the I2C subsystem of 2.4 kernels and early 2.6 +kernels will find out that this method 3 is essentially similar to what +was done there. Two significant differences are: + +* Probing is only one way to instantiate I2C devices now, while it was the + only way back then. Where possible, methods 1 and 2 should be preferred. + Method 3 should only be used when there is no other way, as it can have + undesirable side effects. +* I2C buses must now explicitly say which I2C driver classes can probe + them (by the means of the class bitfield), while all I2C buses were + probed by default back then. The default is an empty class which means + that no probing happens. The purpose of the class bitfield is to limit + the aforementioned undesirable side effects. + +Once again, method 3 should be avoided wherever possible. Explicit device +instantiation (methods 1 and 2) is much preferred for it is safer and +faster. + + +Method 4: Instantiate from user-space +------------------------------------- + +In general, the kernel should know which I2C devices are connected and +what addresses they live at. However, in certain cases, it does not, so a +sysfs interface was added to let the user provide the information. This +interface is made of 2 attribute files which are created in every I2C bus +directory: ``new_device`` and ``delete_device``. Both files are write +only and you must write the right parameters to them in order to properly +instantiate, respectively delete, an I2C device. + +File ``new_device`` takes 2 parameters: the name of the I2C device (a +string) and the address of the I2C device (a number, typically expressed +in hexadecimal starting with 0x, but can also be expressed in decimal.) + +File ``delete_device`` takes a single parameter: the address of the I2C +device. As no two devices can live at the same address on a given I2C +segment, the address is sufficient to uniquely identify the device to be +deleted. + +Example:: + + # echo eeprom 0x50 > /sys/bus/i2c/devices/i2c-3/new_device + +While this interface should only be used when in-kernel device declaration +can't be done, there is a variety of cases where it can be helpful: + +* The I2C driver usually detects devices (method 3 above) but the bus + segment your device lives on doesn't have the proper class bit set and + thus detection doesn't trigger. +* The I2C driver usually detects devices, but your device lives at an + unexpected address. +* The I2C driver usually detects devices, but your device is not detected, + either because the detection routine is too strict, or because your + device is not officially supported yet but you know it is compatible. +* You are developing a driver on a test board, where you soldered the I2C + device yourself. + +This interface is a replacement for the force_* module parameters some I2C +drivers implement. Being implemented in i2c-core rather than in each +device driver individually, it is much more efficient, and also has the +advantage that you do not have to reload the driver to change a setting. +You can also instantiate the device before the driver is loaded or even +available, and you don't need to know what driver the device needs. diff --git a/Documentation/i2c/muxes/i2c-mux-gpio.rst b/Documentation/i2c/muxes/i2c-mux-gpio.rst new file mode 100644 index 0000000000..7d27444035 --- /dev/null +++ b/Documentation/i2c/muxes/i2c-mux-gpio.rst @@ -0,0 +1,85 @@ +========================== +Kernel driver i2c-mux-gpio +========================== + +Author: Peter Korsgaard <peter.korsgaard@barco.com> + +Description +----------- + +i2c-mux-gpio is an i2c mux driver providing access to I2C bus segments +from a master I2C bus and a hardware MUX controlled through GPIO pins. + +E.G.:: + + ---------- ---------- Bus segment 1 - - - - - + | | SCL/SDA | |-------------- | | + | |------------| | + | | | | Bus segment 2 | | + | Linux | GPIO 1..N | MUX |--------------- Devices + | |------------| | | | + | | | | Bus segment M + | | | |---------------| | + ---------- ---------- - - - - - + +SCL/SDA of the master I2C bus is multiplexed to bus segment 1..M +according to the settings of the GPIO pins 1..N. + +Usage +----- + +i2c-mux-gpio uses the platform bus, so you need to provide a struct +platform_device with the platform_data pointing to a struct +i2c_mux_gpio_platform_data with the I2C adapter number of the master +bus, the number of bus segments to create and the GPIO pins used +to control it. See include/linux/platform_data/i2c-mux-gpio.h for details. + +E.G. something like this for a MUX providing 4 bus segments +controlled through 3 GPIO pins:: + + #include <linux/platform_data/i2c-mux-gpio.h> + #include <linux/platform_device.h> + + static const unsigned myboard_gpiomux_gpios[] = { + AT91_PIN_PC26, AT91_PIN_PC25, AT91_PIN_PC24 + }; + + static const unsigned myboard_gpiomux_values[] = { + 0, 1, 2, 3 + }; + + static struct i2c_mux_gpio_platform_data myboard_i2cmux_data = { + .parent = 1, + .base_nr = 2, /* optional */ + .values = myboard_gpiomux_values, + .n_values = ARRAY_SIZE(myboard_gpiomux_values), + .gpios = myboard_gpiomux_gpios, + .n_gpios = ARRAY_SIZE(myboard_gpiomux_gpios), + .idle = 4, /* optional */ + }; + + static struct platform_device myboard_i2cmux = { + .name = "i2c-mux-gpio", + .id = 0, + .dev = { + .platform_data = &myboard_i2cmux_data, + }, + }; + +If you don't know the absolute GPIO pin numbers at registration time, +you can instead provide a chip name (.chip_name) and relative GPIO pin +numbers, and the i2c-mux-gpio driver will do the work for you, +including deferred probing if the GPIO chip isn't immediately +available. + +Device Registration +------------------- + +When registering your i2c-mux-gpio device, you should pass the number +of any GPIO pin it uses as the device ID. This guarantees that every +instance has a different ID. + +Alternatively, if you don't need a stable device name, you can simply +pass PLATFORM_DEVID_AUTO as the device ID, and the platform core will +assign a dynamic ID to your device. If you do not know the absolute +GPIO pin numbers at registration time, this is even the only option. diff --git a/Documentation/i2c/old-module-parameters.rst b/Documentation/i2c/old-module-parameters.rst new file mode 100644 index 0000000000..b08b6daabc --- /dev/null +++ b/Documentation/i2c/old-module-parameters.rst @@ -0,0 +1,55 @@ +================================================================ +I2C device driver binding control from user-space in old kernels +================================================================ + +.. NOTE:: + Note: this section is only relevant if you are handling some old code + found in kernel 2.6. If you work with more recent kernels, you can + safely skip this section. + +Up to kernel 2.6.32, many I2C drivers used helper macros provided by +<linux/i2c.h> which created standard module parameters to let the user +control how the driver would probe I2C buses and attach to devices. These +parameters were known as ``probe`` (to let the driver probe for an extra +address), ``force`` (to forcibly attach the driver to a given device) and +``ignore`` (to prevent a driver from probing a given address). + +With the conversion of the I2C subsystem to the standard device driver +binding model, it became clear that these per-module parameters were no +longer needed, and that a centralized implementation was possible. The new, +sysfs-based interface is described in +Documentation/i2c/instantiating-devices.rst, section +"Method 4: Instantiate from user-space". + +Below is a mapping from the old module parameters to the new interface. + +Attaching a driver to an I2C device +----------------------------------- + +Old method (module parameters):: + + # modprobe <driver> probe=1,0x2d + # modprobe <driver> force=1,0x2d + # modprobe <driver> force_<device>=1,0x2d + +New method (sysfs interface):: + + # echo <device> 0x2d > /sys/bus/i2c/devices/i2c-1/new_device + +Preventing a driver from attaching to an I2C device +--------------------------------------------------- + +Old method (module parameters):: + + # modprobe <driver> ignore=1,0x2f + +New method (sysfs interface):: + + # echo dummy 0x2f > /sys/bus/i2c/devices/i2c-1/new_device + # modprobe <driver> + +Of course, it is important to instantiate the ``dummy`` device before loading +the driver. The dummy device will be handled by i2c-core itself, preventing +other drivers from binding to it later on. If there is a real device at the +problematic address, and you want another driver to bind to it, then simply +pass the name of the device in question instead of ``dummy``. diff --git a/Documentation/i2c/slave-eeprom-backend.rst b/Documentation/i2c/slave-eeprom-backend.rst new file mode 100644 index 0000000000..38d951f103 --- /dev/null +++ b/Documentation/i2c/slave-eeprom-backend.rst @@ -0,0 +1,26 @@ +============================== +Linux I2C slave EEPROM backend +============================== + +by Wolfram Sang <wsa@sang-engineering.com> in 2014-20 + +This backend simulates an EEPROM on the connected I2C bus. Its memory contents +can be accessed from userspace via this file located in sysfs:: + + /sys/bus/i2c/devices/<device-directory>/slave-eeprom + +The following types are available: 24c02, 24c32, 24c64, and 24c512. Read-only +variants are also supported. The name needed for instantiating has the form +'slave-<type>[ro]'. Examples follow: + +24c02, read/write, address 0x64: + # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-1/new_device + +24c512, read-only, address 0x42: + # echo slave-24c512ro 0x1042 > /sys/bus/i2c/devices/i2c-1/new_device + +You can also preload data during boot if a device-property named +'firmware-name' contains a valid filename (DT or ACPI only). + +As of 2015, Linux doesn't support poll on binary sysfs files, so there is no +notification when another master changed the content. diff --git a/Documentation/i2c/slave-interface.rst b/Documentation/i2c/slave-interface.rst new file mode 100644 index 0000000000..3f0d320bc8 --- /dev/null +++ b/Documentation/i2c/slave-interface.rst @@ -0,0 +1,201 @@ +===================================== +Linux I2C slave interface description +===================================== + +by Wolfram Sang <wsa@sang-engineering.com> in 2014-15 + +Linux can also be an I2C slave if the I2C controller in use has slave +functionality. For that to work, one needs slave support in the bus driver plus +a hardware independent software backend providing the actual functionality. An +example for the latter is the slave-eeprom driver, which acts as a dual memory +driver. While another I2C master on the bus can access it like a regular +EEPROM, the Linux I2C slave can access the content via sysfs and handle data as +needed. The backend driver and the I2C bus driver communicate via events. Here +is a small graph visualizing the data flow and the means by which data is +transported. The dotted line marks only one example. The backend could also +use a character device, be in-kernel only, or something completely different:: + + + e.g. sysfs I2C slave events I/O registers + +-----------+ v +---------+ v +--------+ v +------------+ + | Userspace +........+ Backend +-----------+ Driver +-----+ Controller | + +-----------+ +---------+ +--------+ +------------+ + | | + ----------------------------------------------------------------+-- I2C + --------------------------------------------------------------+---- Bus + +Note: Technically, there is also the I2C core between the backend and the +driver. However, at this time of writing, the layer is transparent. + + +User manual +=========== + +I2C slave backends behave like standard I2C clients. So, you can instantiate +them as described in the document instantiating-devices.rst. The only +difference is that i2c slave backends have their own address space. So, you +have to add 0x1000 to the address you would originally request. An example for +instantiating the slave-eeprom driver from userspace at the 7 bit address 0x64 +on bus 1:: + + # echo slave-24c02 0x1064 > /sys/bus/i2c/devices/i2c-1/new_device + +Each backend should come with separate documentation to describe its specific +behaviour and setup. + + +Developer manual +================ + +First, the events which are used by the bus driver and the backend will be +described in detail. After that, some implementation hints for extending bus +drivers and writing backends will be given. + + +I2C slave events +---------------- + +The bus driver sends an event to the backend using the following function:: + + ret = i2c_slave_event(client, event, &val) + +'client' describes the I2C slave device. 'event' is one of the special event +types described hereafter. 'val' holds an u8 value for the data byte to be +read/written and is thus bidirectional. The pointer to val must always be +provided even if val is not used for an event, i.e. don't use NULL here. 'ret' +is the return value from the backend. Mandatory events must be provided by the +bus drivers and must be checked for by backend drivers. + +Event types: + +* I2C_SLAVE_WRITE_REQUESTED (mandatory) + + 'val': unused + + 'ret': 0 if the backend is ready, otherwise some errno + +Another I2C master wants to write data to us. This event should be sent once +our own address and the write bit was detected. The data did not arrive yet, so +there is nothing to process or return. After returning, the bus driver must +always ack the address phase. If 'ret' is zero, backend initialization or +wakeup is done and further data may be received. If 'ret' is an errno, the bus +driver should nack all incoming bytes until the next stop condition to enforce +a retry of the transmission. + +* I2C_SLAVE_READ_REQUESTED (mandatory) + + 'val': backend returns first byte to be sent + + 'ret': always 0 + +Another I2C master wants to read data from us. This event should be sent once +our own address and the read bit was detected. After returning, the bus driver +should transmit the first byte. + +* I2C_SLAVE_WRITE_RECEIVED (mandatory) + + 'val': bus driver delivers received byte + + 'ret': 0 if the byte should be acked, some errno if the byte should be nacked + +Another I2C master has sent a byte to us which needs to be set in 'val'. If 'ret' +is zero, the bus driver should ack this byte. If 'ret' is an errno, then the byte +should be nacked. + +* I2C_SLAVE_READ_PROCESSED (mandatory) + + 'val': backend returns next byte to be sent + + 'ret': always 0 + +The bus driver requests the next byte to be sent to another I2C master in +'val'. Important: This does not mean that the previous byte has been acked, it +only means that the previous byte is shifted out to the bus! To ensure seamless +transmission, most hardware requests the next byte when the previous one is +still shifted out. If the master sends NACK and stops reading after the byte +currently shifted out, this byte requested here is never used. It very likely +needs to be sent again on the next I2C_SLAVE_READ_REQUEST, depending a bit on +your backend, though. + +* I2C_SLAVE_STOP (mandatory) + + 'val': unused + + 'ret': always 0 + +A stop condition was received. This can happen anytime and the backend should +reset its state machine for I2C transfers to be able to receive new requests. + + +Software backends +----------------- + +If you want to write a software backend: + +* use a standard i2c_driver and its matching mechanisms +* write the slave_callback which handles the above slave events + (best using a state machine) +* register this callback via i2c_slave_register() + +Check the i2c-slave-eeprom driver as an example. + + +Bus driver support +------------------ + +If you want to add slave support to the bus driver: + +* implement calls to register/unregister the slave and add those to the + struct i2c_algorithm. When registering, you probably need to set the I2C + slave address and enable slave specific interrupts. If you use runtime pm, you + should use pm_runtime_get_sync() because your device usually needs to be + powered on always to be able to detect its slave address. When unregistering, + do the inverse of the above. + +* Catch the slave interrupts and send appropriate i2c_slave_events to the backend. + +Note that most hardware supports being master _and_ slave on the same bus. So, +if you extend a bus driver, please make sure that the driver supports that as +well. In almost all cases, slave support does not need to disable the master +functionality. + +Check the i2c-rcar driver as an example. + + +About ACK/NACK +-------------- + +It is good behaviour to always ACK the address phase, so the master knows if a +device is basically present or if it mysteriously disappeared. Using NACK to +state being busy is troublesome. SMBus demands to always ACK the address phase, +while the I2C specification is more loose on that. Most I2C controllers also +automatically ACK when detecting their slave addresses, so there is no option +to NACK them. For those reasons, this API does not support NACK in the address +phase. + +Currently, there is no slave event to report if the master did ACK or NACK a +byte when it reads from us. We could make this an optional event if the need +arises. However, cases should be extremely rare because the master is expected +to send STOP after that and we have an event for that. Also, keep in mind not +all I2C controllers have the possibility to report that event. + + +About buffers +------------- + +During development of this API, the question of using buffers instead of just +bytes came up. Such an extension might be possible, usefulness is unclear at +this time of writing. Some points to keep in mind when using buffers: + +* Buffers should be opt-in and backend drivers will always have to support + byte-based transactions as the ultimate fallback anyhow because this is how + the majority of HW works. + +* For backends simulating hardware registers, buffers are largely not helpful + because after each byte written an action should be immediately triggered. + For reads, the data kept in the buffer might get stale if the backend just + updated a register because of internal processing. + +* A master can send STOP at any time. For partially transferred buffers, this + means additional code to handle this exception. Such code tends to be + error-prone. diff --git a/Documentation/i2c/slave-testunit-backend.rst b/Documentation/i2c/slave-testunit-backend.rst new file mode 100644 index 0000000000..ecfc2abec3 --- /dev/null +++ b/Documentation/i2c/slave-testunit-backend.rst @@ -0,0 +1,88 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================================ +Linux I2C slave testunit backend +================================ + +by Wolfram Sang <wsa@sang-engineering.com> in 2020 + +This backend can be used to trigger test cases for I2C bus masters which +require a remote device with certain capabilities (and which are usually not so +easy to obtain). Examples include multi-master testing, and SMBus Host Notify +testing. For some tests, the I2C slave controller must be able to switch +between master and slave mode because it needs to send data, too. + +Note that this is a device for testing and debugging. It should not be enabled +in a production build. And while there is some versioning and we try hard to +keep backward compatibility, there is no stable ABI guaranteed! + +Instantiating the device is regular. Example for bus 0, address 0x30: + +# echo "slave-testunit 0x1030" > /sys/bus/i2c/devices/i2c-0/new_device + +After that, you will have a write-only device listening. Reads will just return +an 8-bit version number of the testunit. When writing, the device consists of 4 +8-bit registers and, except for some "partial" commands, all registers must be +written to start a testcase, i.e. you usually write 4 bytes to the device. The +registers are: + +0x00 CMD - which test to trigger +0x01 DATAL - configuration byte 1 for the test +0x02 DATAH - configuration byte 2 for the test +0x03 DELAY - delay in n * 10ms until test is started + +Using 'i2cset' from the i2c-tools package, the generic command looks like: + +# i2cset -y <bus_num> <testunit_address> <CMD> <DATAL> <DATAH> <DELAY> i + +DELAY is a generic parameter which will delay the execution of the test in CMD. +While a command is running (including the delay), new commands will not be +acknowledged. You need to wait until the old one is completed. + +The commands are described in the following section. An invalid command will +result in the transfer not being acknowledged. + +Commands +-------- + +0x00 NOOP (reserved for future use) + +0x01 READ_BYTES (also needs master mode) + DATAL - address to read data from (lower 7 bits, highest bit currently unused) + DATAH - number of bytes to read + +This is useful to test if your bus master driver is handling multi-master +correctly. You can trigger the testunit to read bytes from another device on +the bus. If the bus master under test also wants to access the bus at the same +time, the bus will be busy. Example to read 128 bytes from device 0x50 after +50ms of delay: + +# i2cset -y 0 0x30 0x01 0x50 0x80 0x05 i + +0x02 SMBUS_HOST_NOTIFY (also needs master mode) + DATAL - low byte of the status word to send + DATAH - high byte of the status word to send + +This test will send an SMBUS_HOST_NOTIFY message to the host. Note that the +status word is currently ignored in the Linux Kernel. Example to send a +notification after 10ms: + +# i2cset -y 0 0x30 0x02 0x42 0x64 0x01 i + +0x03 SMBUS_BLOCK_PROC_CALL (partial command) + DATAL - must be '1', i.e. one further byte will be written + DATAH - number of bytes to be sent back + DELAY - not applicable, partial command! + +This test will respond to a block process call as defined by the SMBus +specification. The one data byte written specifies how many bytes will be sent +back in the following read transfer. Note that in this read transfer, the +testunit will prefix the length of the bytes to follow. So, if your host bus +driver emulates SMBus calls like the majority does, it needs to support the +I2C_M_RECV_LEN flag of an i2c_msg. This is a good testcase for it. The returned +data consists of the length first, and then of an array of bytes from length-1 +to 0. Here is an example which emulates i2c_smbus_block_process_call() using +i2ctransfer (you need i2c-tools v4.2 or later): + +# i2ctransfer -y 0 w3@0x30 0x03 0x01 0x10 r? +0x10 0x0f 0x0e 0x0d 0x0c 0x0b 0x0a 0x09 0x08 0x07 0x06 0x05 0x04 0x03 0x02 0x01 0x00 diff --git a/Documentation/i2c/smbus-protocol.rst b/Documentation/i2c/smbus-protocol.rst new file mode 100644 index 0000000000..adc87456c9 --- /dev/null +++ b/Documentation/i2c/smbus-protocol.rst @@ -0,0 +1,324 @@ +================== +The SMBus Protocol +================== + +The following is a summary of the SMBus protocol. It applies to +all revisions of the protocol (1.0, 1.1, and 2.0). +Certain protocol features which are not supported by +this package are briefly described at the end of this document. + +Some adapters understand only the SMBus (System Management Bus) protocol, +which is a subset from the I2C protocol. Fortunately, many devices use +only the same subset, which makes it possible to put them on an SMBus. + +If you write a driver for some I2C device, please try to use the SMBus +commands if at all possible (if the device uses only that subset of the +I2C protocol). This makes it possible to use the device driver on both +SMBus adapters and I2C adapters (the SMBus command set is automatically +translated to I2C on I2C adapters, but plain I2C commands can not be +handled at all on most pure SMBus adapters). + +Below is a list of SMBus protocol operations, and the functions executing +them. Note that the names used in the SMBus protocol specifications usually +don't match these function names. For some of the operations which pass a +single data byte, the functions using SMBus protocol operation names execute +a different protocol operation entirely. + +Each transaction type corresponds to a functionality flag. Before calling a +transaction function, a device driver should always check (just once) for +the corresponding functionality flag to ensure that the underlying I2C +adapter supports the transaction in question. See +Documentation/i2c/functionality.rst for the details. + + +Key to symbols +============== + +=============== ============================================================= +S Start condition +Sr Repeated start condition, used to switch from write to + read mode. +P Stop condition +Rd/Wr (1 bit) Read/Write bit. Rd equals 1, Wr equals 0. +A, NA (1 bit) Acknowledge (ACK) and Not Acknowledge (NACK) bit +Addr (7 bits) I2C 7 bit address. Note that this can be expanded to + get a 10 bit I2C address. +Comm (8 bits) Command byte, a data byte which often selects a register on + the device. +Data (8 bits) A plain data byte. DataLow and DataHigh represent the low and + high byte of a 16 bit word. +Count (8 bits) A data byte containing the length of a block operation. + +[..] Data sent by I2C device, as opposed to data sent by the host + adapter. +=============== ============================================================= + + +SMBus Quick Command +=================== + +This sends a single bit to the device, at the place of the Rd/Wr bit:: + + S Addr Rd/Wr [A] P + +Functionality flag: I2C_FUNC_SMBUS_QUICK + + +SMBus Receive Byte +================== + +Implemented by i2c_smbus_read_byte() + +This reads a single byte from a device, without specifying a device +register. Some devices are so simple that this interface is enough; for +others, it is a shorthand if you want to read the same register as in +the previous SMBus command:: + + S Addr Rd [A] [Data] NA P + +Functionality flag: I2C_FUNC_SMBUS_READ_BYTE + + +SMBus Send Byte +=============== + +Implemented by i2c_smbus_write_byte() + +This operation is the reverse of Receive Byte: it sends a single byte +to a device. See Receive Byte for more information. + +:: + + S Addr Wr [A] Data [A] P + +Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE + + +SMBus Read Byte +=============== + +Implemented by i2c_smbus_read_byte_data() + +This reads a single byte from a device, from a designated register. +The register is specified through the Comm byte:: + + S Addr Wr [A] Comm [A] Sr Addr Rd [A] [Data] NA P + +Functionality flag: I2C_FUNC_SMBUS_READ_BYTE_DATA + + +SMBus Read Word +=============== + +Implemented by i2c_smbus_read_word_data() + +This operation is very like Read Byte; again, data is read from a +device, from a designated register that is specified through the Comm +byte. But this time, the data is a complete word (16 bits):: + + S Addr Wr [A] Comm [A] Sr Addr Rd [A] [DataLow] A [DataHigh] NA P + +Functionality flag: I2C_FUNC_SMBUS_READ_WORD_DATA + +Note the convenience function i2c_smbus_read_word_swapped() is +available for reads where the two data bytes are the other way +around (not SMBus compliant, but very popular.) + + +SMBus Write Byte +================ + +Implemented by i2c_smbus_write_byte_data() + +This writes a single byte to a device, to a designated register. The +register is specified through the Comm byte. This is the opposite of +the Read Byte operation. + +:: + + S Addr Wr [A] Comm [A] Data [A] P + +Functionality flag: I2C_FUNC_SMBUS_WRITE_BYTE_DATA + + +SMBus Write Word +================ + +Implemented by i2c_smbus_write_word_data() + +This is the opposite of the Read Word operation. 16 bits +of data are written to a device, to the designated register that is +specified through the Comm byte:: + + S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] P + +Functionality flag: I2C_FUNC_SMBUS_WRITE_WORD_DATA + +Note the convenience function i2c_smbus_write_word_swapped() is +available for writes where the two data bytes are the other way +around (not SMBus compliant, but very popular.) + + +SMBus Process Call +================== + +This command selects a device register (through the Comm byte), sends +16 bits of data to it, and reads 16 bits of data in return:: + + S Addr Wr [A] Comm [A] DataLow [A] DataHigh [A] + Sr Addr Rd [A] [DataLow] A [DataHigh] NA P + +Functionality flag: I2C_FUNC_SMBUS_PROC_CALL + + +SMBus Block Read +================ + +Implemented by i2c_smbus_read_block_data() + +This command reads a block of up to 32 bytes from a device, from a +designated register that is specified through the Comm byte. The amount +of data is specified by the device in the Count byte. + +:: + + S Addr Wr [A] Comm [A] + Sr Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P + +Functionality flag: I2C_FUNC_SMBUS_READ_BLOCK_DATA + + +SMBus Block Write +================= + +Implemented by i2c_smbus_write_block_data() + +The opposite of the Block Read command, this writes up to 32 bytes to +a device, to a designated register that is specified through the +Comm byte. The amount of data is specified in the Count byte. + +:: + + S Addr Wr [A] Comm [A] Count [A] Data [A] Data [A] ... [A] Data [A] P + +Functionality flag: I2C_FUNC_SMBUS_WRITE_BLOCK_DATA + + +SMBus Block Write - Block Read Process Call +=========================================== + +SMBus Block Write - Block Read Process Call was introduced in +Revision 2.0 of the specification. + +This command selects a device register (through the Comm byte), sends +1 to 31 bytes of data to it, and reads 1 to 31 bytes of data in return:: + + S Addr Wr [A] Comm [A] Count [A] Data [A] ... + Sr Addr Rd [A] [Count] A [Data] ... A P + +Functionality flag: I2C_FUNC_SMBUS_BLOCK_PROC_CALL + + +SMBus Host Notify +================= + +This command is sent from a SMBus device acting as a master to the +SMBus host acting as a slave. +It is the same form as Write Word, with the command code replaced by the +alerting device's address. + +:: + + [S] [HostAddr] [Wr] A [DevAddr] A [DataLow] A [DataHigh] A [P] + +This is implemented in the following way in the Linux kernel: + +* I2C bus drivers which support SMBus Host Notify should report + I2C_FUNC_SMBUS_HOST_NOTIFY. +* I2C bus drivers trigger SMBus Host Notify by a call to + i2c_handle_smbus_host_notify(). +* I2C drivers for devices which can trigger SMBus Host Notify will have + client->irq assigned to a Host Notify IRQ if no one else specified another. + +There is currently no way to retrieve the data parameter from the client. + + +Packet Error Checking (PEC) +=========================== + +Packet Error Checking was introduced in Revision 1.1 of the specification. + +PEC adds a CRC-8 error-checking byte to transfers using it, immediately +before the terminating STOP. + + +Address Resolution Protocol (ARP) +================================= + +The Address Resolution Protocol was introduced in Revision 2.0 of +the specification. It is a higher-layer protocol which uses the +messages above. + +ARP adds device enumeration and dynamic address assignment to +the protocol. All ARP communications use slave address 0x61 and +require PEC checksums. + + +SMBus Alert +=========== + +SMBus Alert was introduced in Revision 1.0 of the specification. + +The SMBus alert protocol allows several SMBus slave devices to share a +single interrupt pin on the SMBus master, while still allowing the master +to know which slave triggered the interrupt. + +This is implemented the following way in the Linux kernel: + +* I2C bus drivers which support SMBus alert should call + i2c_new_smbus_alert_device() to install SMBus alert support. +* I2C drivers for devices which can trigger SMBus alerts should implement + the optional alert() callback. + + +I2C Block Transactions +====================== + +The following I2C block transactions are similar to the SMBus Block Read +and Write operations, except these do not have a Count byte. They are +supported by the SMBus layer and are described here for completeness, but +they are *NOT* defined by the SMBus specification. + +I2C block transactions do not limit the number of bytes transferred +but the SMBus layer places a limit of 32 bytes. + + +I2C Block Read +============== + +Implemented by i2c_smbus_read_i2c_block_data() + +This command reads a block of bytes from a device, from a +designated register that is specified through the Comm byte:: + + S Addr Wr [A] Comm [A] + Sr Addr Rd [A] [Data] A [Data] A ... A [Data] NA P + +Functionality flag: I2C_FUNC_SMBUS_READ_I2C_BLOCK + + +I2C Block Write +=============== + +Implemented by i2c_smbus_write_i2c_block_data() + +The opposite of the Block Read command, this writes bytes to +a device, to a designated register that is specified through the +Comm byte. Note that command lengths of 0, 2, or more bytes are +supported as they are indistinguishable from data. + +:: + + S Addr Wr [A] Comm [A] Data [A] Data [A] ... [A] Data [A] P + +Functionality flag: I2C_FUNC_SMBUS_WRITE_I2C_BLOCK diff --git a/Documentation/i2c/summary.rst b/Documentation/i2c/summary.rst new file mode 100644 index 0000000000..786c618ba3 --- /dev/null +++ b/Documentation/i2c/summary.rst @@ -0,0 +1,61 @@ +============================= +Introduction to I2C and SMBus +============================= + +I²C (pronounce: I squared C and written I2C in the kernel documentation) is +a protocol developed by Philips. It is a slow two-wire protocol (variable +speed, up to 400 kHz), with a high speed extension (3.4 MHz). It provides +an inexpensive bus for connecting many types of devices with infrequent or +low bandwidth communications needs. I2C is widely used with embedded +systems. Some systems use variants that don't meet branding requirements, +and so are not advertised as being I2C but come under different names, +e.g. TWI (Two Wire Interface), IIC. + +The latest official I2C specification is the `"I2C-bus specification and user +manual" (UM10204) <https://www.nxp.com/webapp/Download?colCode=UM10204>`_ +published by NXP Semiconductors. However, you need to log-in to the site to +access the PDF. An older version of the specification (revision 6) is archived +`here <https://web.archive.org/web/20210813122132/https://www.nxp.com/docs/en/user-guide/UM10204.pdf>`_. + +SMBus (System Management Bus) is based on the I2C protocol, and is mostly +a subset of I2C protocols and signaling. Many I2C devices will work on an +SMBus, but some SMBus protocols add semantics beyond what is required to +achieve I2C branding. Modern PC mainboards rely on SMBus. The most common +devices connected through SMBus are RAM modules configured using I2C EEPROMs, +and hardware monitoring chips. + +Because the SMBus is mostly a subset of the generalized I2C bus, we can +use its protocols on many I2C systems. However, there are systems that don't +meet both SMBus and I2C electrical constraints; and others which can't +implement all the common SMBus protocol semantics or messages. + + +Terminology +=========== + +Using the terminology from the official documentation, the I2C bus connects +one or more *master* chips and one or more *slave* chips. + +.. kernel-figure:: i2c_bus.svg + :alt: Simple I2C bus with one master and 3 slaves + + Simple I2C bus + +A **master** chip is a node that starts communications with slaves. In the +Linux kernel implementation it is called an **adapter** or bus. Adapter +drivers are in the ``drivers/i2c/busses/`` subdirectory. + +An **algorithm** contains general code that can be used to implement a +whole class of I2C adapters. Each specific adapter driver either depends on +an algorithm driver in the ``drivers/i2c/algos/`` subdirectory, or includes +its own implementation. + +A **slave** chip is a node that responds to communications when addressed +by the master. In Linux it is called a **client**. Client drivers are kept +in a directory specific to the feature they provide, for example +``drivers/media/gpio/`` for GPIO expanders and ``drivers/media/i2c/`` for +video-related chips. + +For the example configuration in figure, you will need a driver for your +I2C adapter, and drivers for your I2C devices (usually one driver for each +device). diff --git a/Documentation/i2c/ten-bit-addresses.rst b/Documentation/i2c/ten-bit-addresses.rst new file mode 100644 index 0000000000..5c765aff16 --- /dev/null +++ b/Documentation/i2c/ten-bit-addresses.rst @@ -0,0 +1,33 @@ +===================== +I2C Ten-bit Addresses +===================== + +The I2C protocol knows about two kinds of device addresses: normal 7 bit +addresses, and an extended set of 10 bit addresses. The sets of addresses +do not intersect: the 7 bit address 0x10 is not the same as the 10 bit +address 0x10 (though a single device could respond to both of them). +To avoid ambiguity, the user sees 10 bit addresses mapped to a different +address space, namely 0xa000-0xa3ff. The leading 0xa (= 10) represents the +10 bit mode. This is used for creating device names in sysfs. It is also +needed when instantiating 10 bit devices via the new_device file in sysfs. + +I2C messages to and from 10-bit address devices have a different format. +See the I2C specification for the details. + +The current 10 bit address support is minimal. It should work, however +you can expect some problems along the way: + +* Not all bus drivers support 10-bit addresses. Some don't because the + hardware doesn't support them (SMBus doesn't require 10-bit address + support for example), some don't because nobody bothered adding the + code (or it's there but not working properly.) Software implementation + (i2c-algo-bit) is known to work. +* Some optional features do not support 10-bit addresses. This is the + case of automatic detection and instantiation of devices by their, + drivers, for example. +* Many user-space packages (for example i2c-tools) lack support for + 10-bit addresses. + +Note that 10-bit address devices are still pretty rare, so the limitations +listed above could stay for a long time, maybe even forever if nobody +needs them to be fixed. diff --git a/Documentation/i2c/writing-clients.rst b/Documentation/i2c/writing-clients.rst new file mode 100644 index 0000000000..41ddc10f1a --- /dev/null +++ b/Documentation/i2c/writing-clients.rst @@ -0,0 +1,428 @@ +=============================== +Implementing I2C device drivers +=============================== + +This is a small guide for those who want to write kernel drivers for I2C +or SMBus devices, using Linux as the protocol host/master (not slave). + +To set up a driver, you need to do several things. Some are optional, and +some things can be done slightly or completely different. Use this as a +guide, not as a rule book! + + +General remarks +=============== + +Try to keep the kernel namespace as clean as possible. The best way to +do this is to use a unique prefix for all global symbols. This is +especially important for exported symbols, but it is a good idea to do +it for non-exported symbols too. We will use the prefix ``foo_`` in this +tutorial. + + +The driver structure +==================== + +Usually, you will implement a single driver structure, and instantiate +all clients from it. Remember, a driver structure contains general access +routines, and should be zero-initialized except for fields with data you +provide. A client structure holds device-specific information like the +driver model device node, and its I2C address. + +:: + + static struct i2c_device_id foo_idtable[] = { + { "foo", my_id_for_foo }, + { "bar", my_id_for_bar }, + { } + }; + + MODULE_DEVICE_TABLE(i2c, foo_idtable); + + static struct i2c_driver foo_driver = { + .driver = { + .name = "foo", + .pm = &foo_pm_ops, /* optional */ + }, + + .id_table = foo_idtable, + .probe = foo_probe, + .remove = foo_remove, + /* if device autodetection is needed: */ + .class = I2C_CLASS_SOMETHING, + .detect = foo_detect, + .address_list = normal_i2c, + + .shutdown = foo_shutdown, /* optional */ + .command = foo_command, /* optional, deprecated */ + } + +The name field is the driver name, and must not contain spaces. It +should match the module name (if the driver can be compiled as a module), +although you can use MODULE_ALIAS (passing "foo" in this example) to add +another name for the module. If the driver name doesn't match the module +name, the module won't be automatically loaded (hotplug/coldplug). + +All other fields are for call-back functions which will be explained +below. + + +Extra client data +================= + +Each client structure has a special ``data`` field that can point to any +structure at all. You should use this to keep device-specific data. + +:: + + /* store the value */ + void i2c_set_clientdata(struct i2c_client *client, void *data); + + /* retrieve the value */ + void *i2c_get_clientdata(const struct i2c_client *client); + +Note that starting with kernel 2.6.34, you don't have to set the ``data`` field +to NULL in remove() or if probe() failed anymore. The i2c-core does this +automatically on these occasions. Those are also the only times the core will +touch this field. + + +Accessing the client +==================== + +Let's say we have a valid client structure. At some time, we will need +to gather information from the client, or write new information to the +client. + +I have found it useful to define foo_read and foo_write functions for this. +For some cases, it will be easier to call the I2C functions directly, +but many chips have some kind of register-value idea that can easily +be encapsulated. + +The below functions are simple examples, and should not be copied +literally:: + + int foo_read_value(struct i2c_client *client, u8 reg) + { + if (reg < 0x10) /* byte-sized register */ + return i2c_smbus_read_byte_data(client, reg); + else /* word-sized register */ + return i2c_smbus_read_word_data(client, reg); + } + + int foo_write_value(struct i2c_client *client, u8 reg, u16 value) + { + if (reg == 0x10) /* Impossible to write - driver error! */ + return -EINVAL; + else if (reg < 0x10) /* byte-sized register */ + return i2c_smbus_write_byte_data(client, reg, value); + else /* word-sized register */ + return i2c_smbus_write_word_data(client, reg, value); + } + + +Probing and attaching +===================== + +The Linux I2C stack was originally written to support access to hardware +monitoring chips on PC motherboards, and thus used to embed some assumptions +that were more appropriate to SMBus (and PCs) than to I2C. One of these +assumptions was that most adapters and devices drivers support the SMBUS_QUICK +protocol to probe device presence. Another was that devices and their drivers +can be sufficiently configured using only such probe primitives. + +As Linux and its I2C stack became more widely used in embedded systems +and complex components such as DVB adapters, those assumptions became more +problematic. Drivers for I2C devices that issue interrupts need more (and +different) configuration information, as do drivers handling chip variants +that can't be distinguished by protocol probing, or which need some board +specific information to operate correctly. + + +Device/Driver Binding +--------------------- + +System infrastructure, typically board-specific initialization code or +boot firmware, reports what I2C devices exist. For example, there may be +a table, in the kernel or from the boot loader, identifying I2C devices +and linking them to board-specific configuration information about IRQs +and other wiring artifacts, chip type, and so on. That could be used to +create i2c_client objects for each I2C device. + +I2C device drivers using this binding model work just like any other +kind of driver in Linux: they provide a probe() method to bind to +those devices, and a remove() method to unbind. + +:: + + static int foo_probe(struct i2c_client *client); + static void foo_remove(struct i2c_client *client); + +Remember that the i2c_driver does not create those client handles. The +handle may be used during foo_probe(). If foo_probe() reports success +(zero not a negative status code) it may save the handle and use it until +foo_remove() returns. That binding model is used by most Linux drivers. + +The probe function is called when an entry in the id_table name field +matches the device's name. If the probe function needs that entry, it +can retrieve it using + +:: + + const struct i2c_device_id *id = i2c_match_id(foo_idtable, client); + + +Device Creation +--------------- + +If you know for a fact that an I2C device is connected to a given I2C bus, +you can instantiate that device by simply filling an i2c_board_info +structure with the device address and driver name, and calling +i2c_new_client_device(). This will create the device, then the driver core +will take care of finding the right driver and will call its probe() method. +If a driver supports different device types, you can specify the type you +want using the type field. You can also specify an IRQ and platform data +if needed. + +Sometimes you know that a device is connected to a given I2C bus, but you +don't know the exact address it uses. This happens on TV adapters for +example, where the same driver supports dozens of slightly different +models, and I2C device addresses change from one model to the next. In +that case, you can use the i2c_new_scanned_device() variant, which is +similar to i2c_new_client_device(), except that it takes an additional list +of possible I2C addresses to probe. A device is created for the first +responsive address in the list. If you expect more than one device to be +present in the address range, simply call i2c_new_scanned_device() that +many times. + +The call to i2c_new_client_device() or i2c_new_scanned_device() typically +happens in the I2C bus driver. You may want to save the returned i2c_client +reference for later use. + + +Device Detection +---------------- + +Sometimes you do not know in advance which I2C devices are connected to +a given I2C bus. This is for example the case of hardware monitoring +devices on a PC's SMBus. In that case, you may want to let your driver +detect supported devices automatically. This is how the legacy model +was working, and is now available as an extension to the standard +driver model. + +You simply have to define a detect callback which will attempt to +identify supported devices (returning 0 for supported ones and -ENODEV +for unsupported ones), a list of addresses to probe, and a device type +(or class) so that only I2C buses which may have that type of device +connected (and not otherwise enumerated) will be probed. For example, +a driver for a hardware monitoring chip for which auto-detection is +needed would set its class to I2C_CLASS_HWMON, and only I2C adapters +with a class including I2C_CLASS_HWMON would be probed by this driver. +Note that the absence of matching classes does not prevent the use of +a device of that type on the given I2C adapter. All it prevents is +auto-detection; explicit instantiation of devices is still possible. + +Note that this mechanism is purely optional and not suitable for all +devices. You need some reliable way to identify the supported devices +(typically using device-specific, dedicated identification registers), +otherwise misdetections are likely to occur and things can get wrong +quickly. Keep in mind that the I2C protocol doesn't include any +standard way to detect the presence of a chip at a given address, let +alone a standard way to identify devices. Even worse is the lack of +semantics associated to bus transfers, which means that the same +transfer can be seen as a read operation by a chip and as a write +operation by another chip. For these reasons, explicit device +instantiation should always be preferred to auto-detection where +possible. + + +Device Deletion +--------------- + +Each I2C device which has been created using i2c_new_client_device() +or i2c_new_scanned_device() can be unregistered by calling +i2c_unregister_device(). If you don't call it explicitly, it will be +called automatically before the underlying I2C bus itself is removed, +as a device can't survive its parent in the device driver model. + + +Initializing the driver +======================= + +When the kernel is booted, or when your foo driver module is inserted, +you have to do some initializing. Fortunately, just registering the +driver module is usually enough. + +:: + + static int __init foo_init(void) + { + return i2c_add_driver(&foo_driver); + } + module_init(foo_init); + + static void __exit foo_cleanup(void) + { + i2c_del_driver(&foo_driver); + } + module_exit(foo_cleanup); + + The module_i2c_driver() macro can be used to reduce above code. + + module_i2c_driver(foo_driver); + +Note that some functions are marked by ``__init``. These functions can +be removed after kernel booting (or module loading) is completed. +Likewise, functions marked by ``__exit`` are dropped by the compiler when +the code is built into the kernel, as they would never be called. + + +Driver Information +================== + +:: + + /* Substitute your own name and email address */ + MODULE_AUTHOR("Frodo Looijaard <frodol@dds.nl>" + MODULE_DESCRIPTION("Driver for Barf Inc. Foo I2C devices"); + + /* a few non-GPL license types are also allowed */ + MODULE_LICENSE("GPL"); + + +Power Management +================ + +If your I2C device needs special handling when entering a system low +power state -- like putting a transceiver into a low power mode, or +activating a system wakeup mechanism -- do that by implementing the +appropriate callbacks for the dev_pm_ops of the driver (like suspend +and resume). + +These are standard driver model calls, and they work just like they +would for any other driver stack. The calls can sleep, and can use +I2C messaging to the device being suspended or resumed (since their +parent I2C adapter is active when these calls are issued, and IRQs +are still enabled). + + +System Shutdown +=============== + +If your I2C device needs special handling when the system shuts down +or reboots (including kexec) -- like turning something off -- use a +shutdown() method. + +Again, this is a standard driver model call, working just like it +would for any other driver stack: the calls can sleep, and can use +I2C messaging. + + +Command function +================ + +A generic ioctl-like function call back is supported. You will seldom +need this, and its use is deprecated anyway, so newer design should not +use it. + + +Sending and receiving +===================== + +If you want to communicate with your device, there are several functions +to do this. You can find all of them in <linux/i2c.h>. + +If you can choose between plain I2C communication and SMBus level +communication, please use the latter. All adapters understand SMBus level +commands, but only some of them understand plain I2C! + + +Plain I2C communication +----------------------- + +:: + + int i2c_master_send(struct i2c_client *client, const char *buf, + int count); + int i2c_master_recv(struct i2c_client *client, char *buf, int count); + +These routines read and write some bytes from/to a client. The client +contains the I2C address, so you do not have to include it. The second +parameter contains the bytes to read/write, the third the number of bytes +to read/write (must be less than the length of the buffer, also should be +less than 64k since msg.len is u16.) Returned is the actual number of bytes +read/written. + +:: + + int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msg, + int num); + +This sends a series of messages. Each message can be a read or write, +and they can be mixed in any way. The transactions are combined: no +stop condition is issued between transaction. The i2c_msg structure +contains for each message the client address, the number of bytes of the +message and the message data itself. + +You can read the file i2c-protocol.rst for more information about the +actual I2C protocol. + + +SMBus communication +------------------- + +:: + + s32 i2c_smbus_xfer(struct i2c_adapter *adapter, u16 addr, + unsigned short flags, char read_write, u8 command, + int size, union i2c_smbus_data *data); + +This is the generic SMBus function. All functions below are implemented +in terms of it. Never use this function directly! + +:: + + s32 i2c_smbus_read_byte(struct i2c_client *client); + s32 i2c_smbus_write_byte(struct i2c_client *client, u8 value); + s32 i2c_smbus_read_byte_data(struct i2c_client *client, u8 command); + s32 i2c_smbus_write_byte_data(struct i2c_client *client, + u8 command, u8 value); + s32 i2c_smbus_read_word_data(struct i2c_client *client, u8 command); + s32 i2c_smbus_write_word_data(struct i2c_client *client, + u8 command, u16 value); + s32 i2c_smbus_read_block_data(struct i2c_client *client, + u8 command, u8 *values); + s32 i2c_smbus_write_block_data(struct i2c_client *client, + u8 command, u8 length, const u8 *values); + s32 i2c_smbus_read_i2c_block_data(struct i2c_client *client, + u8 command, u8 length, u8 *values); + s32 i2c_smbus_write_i2c_block_data(struct i2c_client *client, + u8 command, u8 length, + const u8 *values); + +These ones were removed from i2c-core because they had no users, but could +be added back later if needed:: + + s32 i2c_smbus_write_quick(struct i2c_client *client, u8 value); + s32 i2c_smbus_process_call(struct i2c_client *client, + u8 command, u16 value); + s32 i2c_smbus_block_process_call(struct i2c_client *client, + u8 command, u8 length, u8 *values); + +All these transactions return a negative errno value on failure. The 'write' +transactions return 0 on success; the 'read' transactions return the read +value, except for block transactions, which return the number of values +read. The block buffers need not be longer than 32 bytes. + +You can read the file smbus-protocol.rst for more information about the +actual SMBus protocol. + + +General purpose routines +======================== + +Below all general purpose routines are listed, that were not mentioned +before:: + + /* Return the adapter number for a specific adapter */ + int i2c_adapter_id(struct i2c_adapter *adap); |
