diff options
Diffstat (limited to 'Documentation/devicetree/bindings/i2c/i2c.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c.txt | 151 |
1 files changed, 151 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt new file mode 100644 index 000000000..fc3dd7ec0 --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c.txt @@ -0,0 +1,151 @@ +Generic device tree bindings for I2C busses +=========================================== + +This document describes generic bindings which can be used to describe I2C +busses and their child devices in a device tree. + +Required properties (per bus) +----------------------------- + +- #address-cells - should be <1>. Read more about addresses below. +- #size-cells - should be <0>. +- compatible - name of I2C bus controller + +For other required properties e.g. to describe register sets, +clocks, etc. check the binding documentation of the specific driver. + +The cells properties above define that an address of children of an I2C bus +are described by a single value. + +Optional properties (per bus) +----------------------------- + +These properties may not be supported by all drivers. However, if a driver +wants to support one of the below features, it should adapt these bindings. + +- clock-frequency + frequency of bus clock in Hz. + +- i2c-bus + For I2C adapters that have child nodes that are a mixture of both I2C + devices and non-I2C devices, the 'i2c-bus' subnode can be used for + populating I2C devices. If the 'i2c-bus' subnode is present, only + subnodes of this will be considered as I2C slaves. The properties, + '#address-cells' and '#size-cells' must be defined under this subnode + if present. + +- i2c-scl-falling-time-ns + Number of nanoseconds the SCL signal takes to fall; t(f) in the I2C + specification. + +- i2c-scl-internal-delay-ns + Number of nanoseconds the IP core additionally needs to setup SCL. + +- i2c-scl-rising-time-ns + Number of nanoseconds the SCL signal takes to rise; t(r) in the I2C + specification. + +- i2c-sda-falling-time-ns + Number of nanoseconds the SDA signal takes to fall; t(f) in the I2C + specification. + +- i2c-analog-filter + Enable analog filter for i2c lines. + +- i2c-digital-filter + Enable digital filter for i2c lines. + +- i2c-digital-filter-width-ns + Width of spikes which can be filtered by digital filter + (i2c-digital-filter). This width is specified in nanoseconds. + +- i2c-analog-filter-cutoff-frequency + Frequency that the analog filter (i2c-analog-filter) uses to distinguish + which signal to filter. Signal with higher frequency than specified will + be filtered out. Only lower frequency will pass (this is applicable to + a low-pass analog filter). Typical value should be above the normal + i2c bus clock frequency (clock-frequency). + Specified in Hz. + +- multi-master + states that there is another master active on this bus. The OS can use + this information to adapt power management to keep the arbitration awake + all the time, for example. Can not be combined with 'single-master'. + +- pinctrl + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus + recovery, call it "gpio" or "recovery" (deprecated) state + +- scl-gpios + specify the gpio related to SCL pin. Used for GPIO bus recovery. + +- sda-gpios + specify the gpio related to SDA pin. Optional for GPIO bus recovery. + +- single-master + states that there is no other master active on this bus. The OS can use + this information to detect a stalled bus more reliably, for example. + Can not be combined with 'multi-master'. + +- smbus + states that additional SMBus restrictions and features apply to this bus. + An example of feature is SMBusHostNotify. Examples of restrictions are + more reserved addresses and timeout definitions. + +- smbus-alert + states that the optional SMBus-Alert feature apply to this bus. + +- mctp-controller + indicates that the system is accessible via this bus as an endpoint for + MCTP over I2C transport. + +Required properties (per child device) +-------------------------------------- + +- compatible + name of I2C slave device + +- reg + One or many I2C slave addresses. These are usually a 7 bit addresses. + However, flags can be attached to an address. I2C_TEN_BIT_ADDRESS is + used to mark a 10 bit address. It is needed to avoid the ambiguity + between e.g. a 7 bit address of 0x50 and a 10 bit address of 0x050 + which, in theory, can be on the same bus. + Another flag is I2C_OWN_SLAVE_ADDRESS to mark addresses on which we + listen to be devices ourselves. + +Optional properties (per child device) +-------------------------------------- + +These properties may not be supported by all drivers. However, if a driver +wants to support one of the below features, it should adapt these bindings. + +- host-notify + device uses SMBus host notify protocol instead of interrupt line. + +- interrupts + interrupts used by the device. + +- interrupt-names + "irq", "wakeup" and "smbus_alert" names are recognized by I2C core, + other names are left to individual drivers. + +- reg-names + Names of map programmable addresses. + It can contain any map needing another address than default one. + +- wakeup-source + device can be used as a wakeup source. + +Binding may contain optional "interrupts" property, describing interrupts +used by the device. I2C core will assign "irq" interrupt (or the very first +interrupt if not using interrupt names) as primary interrupt for the slave. + +Alternatively, devices supporting SMBus Host Notify, and connected to +adapters that support this feature, may use "host-notify" property. I2C +core will create a virtual interrupt for Host Notify and assign it as +primary interrupt for the slave. + +Also, if device is marked as a wakeup source, I2C core will set up "wakeup" +interrupt for the device. If "wakeup" interrupt name is not present in the +binding, then primary interrupt will be used as wakeup interrupt. |