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| -rw-r--r-- | Documentation/acpi/enumeration.txt | 227 |
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diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt new file mode 100644 index 00000000000..4f27785ca0c --- /dev/null +++ b/Documentation/acpi/enumeration.txt @@ -0,0 +1,227 @@ +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: + + o Devices that have no bus connector resource are represented as + platform devices. + + o 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 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. + +Currently the kernel is not able to automatically determine from which ACPI +device it should make the corresponding platform device so we need to add +the ACPI device explicitly to acpi_platform_device_ids list defined in +drivers/acpi/scan.c. This limitation is only for the platform devices, SPI +and I2C devices are created automatically as described below. + +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 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 configation 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. However the I2C bus controller driver +needs to call acpi_i2c_register_devices() after it has added the adapter. + +An I2C bus (controller) driver does: + + ... + ret = i2c_add_numbered_adapter(adapter); + if (ret) + /* handle error */ + + of_i2c_register_devices(adapter); + /* Enumerate the slave devices behind this bus via ACPI */ + acpi_i2c_register_devices(adapter); + +Below is an example of how to add ACPI support to the existing mpu3050 +input driver: + + #ifdef CONFIG_ACPI + static 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 = __devexit_p(mpu3050_remove), + .id_table = mpu3050_ids, + }; + +GPIO support +~~~~~~~~~~~~ +ACPI 5 introduced two new resources to describe GPIO connections: GpioIo +and GpioInt. These resources are used be used to pass GPIO numbers used by +the device to the driver. For example: + + Method (_CRS, 0, NotSerialized) + { + Name (SBUF, ResourceTemplate() + { + GpioIo (Exclusive, PullDefault, 0x0000, 0x0000, + IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0", + 0x00, ResourceConsumer,,) + { + // Pin List + 0x0055 + } + ... + + Return (SBUF) + } + } + +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 Linux GPIO numbers. + +The driver can do this by including <linux/acpi_gpio.h> and then calling +acpi_get_gpio(path, gpio). This will return the Linux GPIO number or +negative errno if there was no translation found. + +Other GpioIo parameters must be converted first by the driver to be +suitable to the gpiolib before passing them. + +In case of GpioInt resource an additional call to gpio_to_irq() must be +done before calling request_irq(). |