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diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst new file mode 100644 index 000000000..c13fee8b0 --- /dev/null +++ b/Documentation/firmware-guide/acpi/enumeration.rst @@ -0,0 +1,463 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============================= +ACPI Based Device Enumeration +============================= + +ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus, +SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave +devices behind serial bus controllers. + +In addition we are starting to see peripherals integrated in the +SoC/Chipset to appear only in ACPI namespace. These are typically devices +that are accessed through memory-mapped registers. + +In order to support this and re-use the existing drivers as much as +possible we decided to do following: + + - Devices that have no bus connector resource are represented as + platform devices. + + - Devices behind real busses where there is a connector resource + are represented as struct spi_device or struct i2c_device + (standard UARTs are not busses so there is no struct uart_device). + +As both ACPI and Device Tree represent a tree of devices (and their +resources) this implementation follows the Device Tree way as much as +possible. + +The ACPI implementation enumerates devices behind busses (platform, SPI and +I2C), creates the physical devices and binds them to their ACPI handle in +the ACPI namespace. + +This means that when ACPI_HANDLE(dev) returns non-NULL the device was +enumerated from ACPI namespace. This handle can be used to extract other +device-specific configuration. There is an example of this below. + +Platform bus support +==================== + +Since we are using platform devices to represent devices that are not +connected to any physical bus we only need to implement a platform driver +for the device and add supported ACPI IDs. If this same IP-block is used on +some other non-ACPI platform, the driver might work out of the box or needs +some minor changes. + +Adding ACPI support for an existing driver should be pretty +straightforward. Here is the simplest example:: + + #ifdef CONFIG_ACPI + static const struct acpi_device_id mydrv_acpi_match[] = { + /* ACPI IDs here */ + { } + }; + MODULE_DEVICE_TABLE(acpi, mydrv_acpi_match); + #endif + + static struct platform_driver my_driver = { + ... + .driver = { + .acpi_match_table = ACPI_PTR(mydrv_acpi_match), + }, + }; + +If the driver needs to perform more complex initialization like getting and +configuring GPIOs it can get its ACPI handle and extract this information +from ACPI tables. + +DMA support +=========== + +DMA controllers enumerated via ACPI should be registered in the system to +provide generic access to their resources. For example, a driver that would +like to be accessible to slave devices via generic API call +dma_request_chan() must register itself at the end of the probe function like +this:: + + err = devm_acpi_dma_controller_register(dev, xlate_func, dw); + /* Handle the error if it's not a case of !CONFIG_ACPI */ + +and implement custom xlate function if needed (usually acpi_dma_simple_xlate() +is enough) which converts the FixedDMA resource provided by struct +acpi_dma_spec into the corresponding DMA channel. A piece of code for that case +could look like:: + + #ifdef CONFIG_ACPI + struct filter_args { + /* Provide necessary information for the filter_func */ + ... + }; + + static bool filter_func(struct dma_chan *chan, void *param) + { + /* Choose the proper channel */ + ... + } + + static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec, + struct acpi_dma *adma) + { + dma_cap_mask_t cap; + struct filter_args args; + + /* Prepare arguments for filter_func */ + ... + return dma_request_channel(cap, filter_func, &args); + } + #else + static struct dma_chan *xlate_func(struct acpi_dma_spec *dma_spec, + struct acpi_dma *adma) + { + return NULL; + } + #endif + +dma_request_chan() will call xlate_func() for each registered DMA controller. +In the xlate function the proper channel must be chosen based on +information in struct acpi_dma_spec and the properties of the controller +provided by struct acpi_dma. + +Clients must call dma_request_chan() with the string parameter that corresponds +to a specific FixedDMA resource. By default "tx" means the first entry of the +FixedDMA resource array, "rx" means the second entry. The table below shows a +layout:: + + Device (I2C0) + { + ... + Method (_CRS, 0, NotSerialized) + { + Name (DBUF, ResourceTemplate () + { + FixedDMA (0x0018, 0x0004, Width32bit, _Y48) + FixedDMA (0x0019, 0x0005, Width32bit, ) + }) + ... + } + } + +So, the FixedDMA with request line 0x0018 is "tx" and next one is "rx" in +this example. + +In robust cases the client unfortunately needs to call +acpi_dma_request_slave_chan_by_index() directly and therefore choose the +specific FixedDMA resource by its index. + +SPI serial bus support +====================== + +Slave devices behind SPI bus have SpiSerialBus resource attached to them. +This is extracted automatically by the SPI core and the slave devices are +enumerated once spi_register_master() is called by the bus driver. + +Here is what the ACPI namespace for a SPI slave might look like:: + + Device (EEP0) + { + Name (_ADR, 1) + Name (_CID, Package() { + "ATML0025", + "AT25", + }) + ... + Method (_CRS, 0, NotSerialized) + { + SPISerialBus(1, PolarityLow, FourWireMode, 8, + ControllerInitiated, 1000000, ClockPolarityLow, + ClockPhaseFirst, "\\_SB.PCI0.SPI1",) + } + ... + +The SPI device drivers only need to add ACPI IDs in a similar way than with +the platform device drivers. Below is an example where we add ACPI support +to at25 SPI eeprom driver (this is meant for the above ACPI snippet):: + + #ifdef CONFIG_ACPI + static const struct acpi_device_id at25_acpi_match[] = { + { "AT25", 0 }, + { }, + }; + MODULE_DEVICE_TABLE(acpi, at25_acpi_match); + #endif + + static struct spi_driver at25_driver = { + .driver = { + ... + .acpi_match_table = ACPI_PTR(at25_acpi_match), + }, + }; + +Note that this driver actually needs more information like page size of the +eeprom etc. but at the time writing this there is no standard way of +passing those. One idea is to return this in _DSM method like:: + + Device (EEP0) + { + ... + Method (_DSM, 4, NotSerialized) + { + Store (Package (6) + { + "byte-len", 1024, + "addr-mode", 2, + "page-size, 32 + }, Local0) + + // Check UUIDs etc. + + Return (Local0) + } + +Then the at25 SPI driver can get this configuration by calling _DSM on its +ACPI handle like:: + + struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL }; + struct acpi_object_list input; + acpi_status status; + + /* Fill in the input buffer */ + + status = acpi_evaluate_object(ACPI_HANDLE(&spi->dev), "_DSM", + &input, &output); + if (ACPI_FAILURE(status)) + /* Handle the error */ + + /* Extract the data here */ + + kfree(output.pointer); + +I2C serial bus support +====================== + +The slaves behind I2C bus controller only need to add the ACPI IDs like +with the platform and SPI drivers. The I2C core automatically enumerates +any slave devices behind the controller device once the adapter is +registered. + +Below is an example of how to add ACPI support to the existing mpu3050 +input driver:: + + #ifdef CONFIG_ACPI + static const struct acpi_device_id mpu3050_acpi_match[] = { + { "MPU3050", 0 }, + { }, + }; + MODULE_DEVICE_TABLE(acpi, mpu3050_acpi_match); + #endif + + static struct i2c_driver mpu3050_i2c_driver = { + .driver = { + .name = "mpu3050", + .owner = THIS_MODULE, + .pm = &mpu3050_pm, + .of_match_table = mpu3050_of_match, + .acpi_match_table = ACPI_PTR(mpu3050_acpi_match), + }, + .probe = mpu3050_probe, + .remove = mpu3050_remove, + .id_table = mpu3050_ids, + }; + +GPIO support +============ + +ACPI 5 introduced two new resources to describe GPIO connections: GpioIo +and GpioInt. These resources can be used to pass GPIO numbers used by +the device to the driver. ACPI 5.1 extended this with _DSD (Device +Specific Data) which made it possible to name the GPIOs among other things. + +For example:: + + Device (DEV) + { + Method (_CRS, 0, NotSerialized) + { + Name (SBUF, ResourceTemplate() + { + ... + // Used to power on/off the device + GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, + IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0", + 0x00, ResourceConsumer,,) + { + // Pin List + 0x0055 + } + + // Interrupt for the device + GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone, + 0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,) + { + // Pin list + 0x0058 + } + + ... + + } + + Return (SBUF) + } + + // ACPI 5.1 _DSD used for naming the GPIOs + Name (_DSD, Package () + { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () + { + Package () {"power-gpios", Package() {^DEV, 0, 0, 0 }}, + Package () {"irq-gpios", Package() {^DEV, 1, 0, 0 }}, + } + }) + ... + +These GPIO numbers are controller relative and path "\\_SB.PCI0.GPI0" +specifies the path to the controller. In order to use these GPIOs in Linux +we need to translate them to the corresponding Linux GPIO descriptors. + +There is a standard GPIO API for that and is documented in +Documentation/admin-guide/gpio/. + +In the above example we can get the corresponding two GPIO descriptors with +a code like this:: + + #include <linux/gpio/consumer.h> + ... + + struct gpio_desc *irq_desc, *power_desc; + + irq_desc = gpiod_get(dev, "irq"); + if (IS_ERR(irq_desc)) + /* handle error */ + + power_desc = gpiod_get(dev, "power"); + if (IS_ERR(power_desc)) + /* handle error */ + + /* Now we can use the GPIO descriptors */ + +There are also devm_* versions of these functions which release the +descriptors once the device is released. + +See Documentation/firmware-guide/acpi/gpio-properties.rst for more information about the +_DSD binding related to GPIOs. + +MFD devices +=========== + +The MFD devices register their children as platform devices. For the child +devices there needs to be an ACPI handle that they can use to reference +parts of the ACPI namespace that relate to them. In the Linux MFD subsystem +we provide two ways: + + - The children share the parent ACPI handle. + - The MFD cell can specify the ACPI id of the device. + +For the first case, the MFD drivers do not need to do anything. The +resulting child platform device will have its ACPI_COMPANION() set to point +to the parent device. + +If the ACPI namespace has a device that we can match using an ACPI id or ACPI +adr, the cell should be set like:: + + static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = { + .pnpid = "XYZ0001", + .adr = 0, + }; + + static struct mfd_cell my_subdevice_cell = { + .name = "my_subdevice", + /* set the resources relative to the parent */ + .acpi_match = &my_subdevice_cell_acpi_match, + }; + +The ACPI id "XYZ0001" is then used to lookup an ACPI device directly under +the MFD device and if found, that ACPI companion device is bound to the +resulting child platform device. + +Device Tree namespace link device ID +==================================== + +The Device Tree protocol uses device identification based on the "compatible" +property whose value is a string or an array of strings recognized as device +identifiers by drivers and the driver core. The set of all those strings may be +regarded as a device identification namespace analogous to the ACPI/PNP device +ID namespace. Consequently, in principle it should not be necessary to allocate +a new (and arguably redundant) ACPI/PNP device ID for a devices with an existing +identification string in the Device Tree (DT) namespace, especially if that ID +is only needed to indicate that a given device is compatible with another one, +presumably having a matching driver in the kernel already. + +In ACPI, the device identification object called _CID (Compatible ID) is used to +list the IDs of devices the given one is compatible with, but those IDs must +belong to one of the namespaces prescribed by the ACPI specification (see +Section 6.1.2 of ACPI 6.0 for details) and the DT namespace is not one of them. +Moreover, the specification mandates that either a _HID or an _ADR identification +object be present for all ACPI objects representing devices (Section 6.1 of ACPI +6.0). For non-enumerable bus types that object must be _HID and its value must +be a device ID from one of the namespaces prescribed by the specification too. + +The special DT namespace link device ID, PRP0001, provides a means to use the +existing DT-compatible device identification in ACPI and to satisfy the above +requirements following from the ACPI specification at the same time. Namely, +if PRP0001 is returned by _HID, the ACPI subsystem will look for the +"compatible" property in the device object's _DSD and will use the value of that +property to identify the corresponding device in analogy with the original DT +device identification algorithm. If the "compatible" property is not present +or its value is not valid, the device will not be enumerated by the ACPI +subsystem. Otherwise, it will be enumerated automatically as a platform device +(except when an I2C or SPI link from the device to its parent is present, in +which case the ACPI core will leave the device enumeration to the parent's +driver) and the identification strings from the "compatible" property value will +be used to find a driver for the device along with the device IDs listed by _CID +(if present). + +Analogously, if PRP0001 is present in the list of device IDs returned by _CID, +the identification strings listed by the "compatible" property value (if present +and valid) will be used to look for a driver matching the device, but in that +case their relative priority with respect to the other device IDs listed by +_HID and _CID depends on the position of PRP0001 in the _CID return package. +Specifically, the device IDs returned by _HID and preceding PRP0001 in the _CID +return package will be checked first. Also in that case the bus type the device +will be enumerated to depends on the device ID returned by _HID. + +For example, the following ACPI sample might be used to enumerate an lm75-type +I2C temperature sensor and match it to the driver using the Device Tree +namespace link:: + + Device (TMP0) + { + Name (_HID, "PRP0001") + Name (_DSD, Package() { + ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), + Package () { + Package (2) { "compatible", "ti,tmp75" }, + } + }) + Method (_CRS, 0, Serialized) + { + Name (SBUF, ResourceTemplate () + { + I2cSerialBusV2 (0x48, ControllerInitiated, + 400000, AddressingMode7Bit, + "\\_SB.PCI0.I2C1", 0x00, + ResourceConsumer, , Exclusive,) + }) + Return (SBUF) + } + } + +It is valid to define device objects with a _HID returning PRP0001 and without +the "compatible" property in the _DSD or a _CID as long as one of their +ancestors provides a _DSD with a valid "compatible" property. Such device +objects are then simply regarded as additional "blocks" providing hierarchical +configuration information to the driver of the composite ancestor device. + +However, PRP0001 can only be returned from either _HID or _CID of a device +object if all of the properties returned by the _DSD associated with it (either +the _DSD of the device object itself or the _DSD of its ancestor in the +"composite device" case described above) can be used in the ACPI environment. +Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible" +property returned by it is meaningless. + +Refer to :doc:`DSD-properties-rules` for more information. |