Documentation: ACPI: move enumeration.txt to firmware-guide/acpi and convert to reST
This converts the plain text documentation to reStructuredText format and adds it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du <changbin.du@gmail.com> Reviewed-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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Changbin Du
Rafael J. Wysocki
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8a2fe04b44
commit
c24bc66e81
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@ -1,5 +1,9 @@
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ACPI based device enumeration
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.. SPDX-License-Identifier: GPL-2.0
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=============================
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ACPI Based Device Enumeration
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=============================
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ACPI 5 introduced a set of new resources (UartTSerialBus, I2cSerialBus,
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SpiSerialBus, GpioIo and GpioInt) which can be used in enumerating slave
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devices behind serial bus controllers.
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@ -11,10 +15,10 @@ that are accessed through memory-mapped registers.
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In order to support this and re-use the existing drivers as much as
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possible we decided to do following:
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o Devices that have no bus connector resource are represented as
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- Devices that have no bus connector resource are represented as
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platform devices.
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o Devices behind real busses where there is a connector resource
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- Devices behind real busses where there is a connector resource
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are represented as struct spi_device or struct i2c_device
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(standard UARTs are not busses so there is no struct uart_device).
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@ -31,7 +35,8 @@ enumerated from ACPI namespace. This handle can be used to extract other
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device-specific configuration. There is an example of this below.
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Platform bus support
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~~~~~~~~~~~~~~~~~~~~
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====================
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Since we are using platform devices to represent devices that are not
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connected to any physical bus we only need to implement a platform driver
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for the device and add supported ACPI IDs. If this same IP-block is used on
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@ -39,7 +44,7 @@ some other non-ACPI platform, the driver might work out of the box or needs
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some minor changes.
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Adding ACPI support for an existing driver should be pretty
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straightforward. Here is the simplest example:
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straightforward. Here is the simplest example::
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#ifdef CONFIG_ACPI
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static const struct acpi_device_id mydrv_acpi_match[] = {
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@ -61,12 +66,13 @@ configuring GPIOs it can get its ACPI handle and extract this information
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from ACPI tables.
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DMA support
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~~~~~~~~~~~
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===========
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DMA controllers enumerated via ACPI should be registered in the system to
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provide generic access to their resources. For example, a driver that would
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like to be accessible to slave devices via generic API call
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dma_request_slave_channel() must register itself at the end of the probe
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function like this:
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function like this::
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err = devm_acpi_dma_controller_register(dev, xlate_func, dw);
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/* Handle the error if it's not a case of !CONFIG_ACPI */
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@ -74,7 +80,7 @@ function like this:
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and implement custom xlate function if needed (usually acpi_dma_simple_xlate()
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is enough) which converts the FixedDMA resource provided by struct
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acpi_dma_spec into the corresponding DMA channel. A piece of code for that case
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could look like:
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could look like::
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#ifdef CONFIG_ACPI
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struct filter_args {
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@ -114,7 +120,7 @@ provided by struct acpi_dma.
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Clients must call dma_request_slave_channel() with the string parameter that
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corresponds to a specific FixedDMA resource. By default "tx" means the first
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entry of the FixedDMA resource array, "rx" means the second entry. The table
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below shows a layout:
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below shows a layout::
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Device (I2C0)
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{
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@ -138,12 +144,13 @@ acpi_dma_request_slave_chan_by_index() directly and therefore choose the
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specific FixedDMA resource by its index.
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SPI serial bus support
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~~~~~~~~~~~~~~~~~~~~~~
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======================
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Slave devices behind SPI bus have SpiSerialBus resource attached to them.
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This is extracted automatically by the SPI core and the slave devices are
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enumerated once spi_register_master() is called by the bus driver.
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Here is what the ACPI namespace for a SPI slave might look like:
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Here is what the ACPI namespace for a SPI slave might look like::
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Device (EEP0)
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{
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@ -163,7 +170,7 @@ Here is what the ACPI namespace for a SPI slave might look like:
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The SPI device drivers only need to add ACPI IDs in a similar way than with
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the platform device drivers. Below is an example where we add ACPI support
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to at25 SPI eeprom driver (this is meant for the above ACPI snippet):
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to at25 SPI eeprom driver (this is meant for the above ACPI snippet)::
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#ifdef CONFIG_ACPI
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static const struct acpi_device_id at25_acpi_match[] = {
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@ -182,7 +189,7 @@ to at25 SPI eeprom driver (this is meant for the above ACPI snippet):
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Note that this driver actually needs more information like page size of the
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eeprom etc. but at the time writing this there is no standard way of
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passing those. One idea is to return this in _DSM method like:
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passing those. One idea is to return this in _DSM method like::
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Device (EEP0)
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{
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@ -202,7 +209,7 @@ passing those. One idea is to return this in _DSM method like:
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}
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Then the at25 SPI driver can get this configuration by calling _DSM on its
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ACPI handle like:
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ACPI handle like::
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struct acpi_buffer output = { ACPI_ALLOCATE_BUFFER, NULL };
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struct acpi_object_list input;
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@ -220,14 +227,15 @@ ACPI handle like:
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kfree(output.pointer);
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I2C serial bus support
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~~~~~~~~~~~~~~~~~~~~~~
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======================
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The slaves behind I2C bus controller only need to add the ACPI IDs like
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with the platform and SPI drivers. The I2C core automatically enumerates
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any slave devices behind the controller device once the adapter is
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registered.
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Below is an example of how to add ACPI support to the existing mpu3050
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input driver:
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input driver::
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#ifdef CONFIG_ACPI
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static const struct acpi_device_id mpu3050_acpi_match[] = {
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@ -251,13 +259,14 @@ input driver:
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};
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GPIO support
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~~~~~~~~~~~~
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============
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ACPI 5 introduced two new resources to describe GPIO connections: GpioIo
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and GpioInt. These resources can be used to pass GPIO numbers used by
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the device to the driver. ACPI 5.1 extended this with _DSD (Device
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Specific Data) which made it possible to name the GPIOs among other things.
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For example:
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For example::
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Device (DEV)
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{
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@ -310,7 +319,7 @@ There is a standard GPIO API for that and is documented in
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Documentation/gpio/.
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In the above example we can get the corresponding two GPIO descriptors with
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a code like this:
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a code like this::
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#include <linux/gpio/consumer.h>
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...
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@ -334,21 +343,22 @@ See Documentation/acpi/gpio-properties.txt for more information about the
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_DSD binding related to GPIOs.
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MFD devices
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~~~~~~~~~~~
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===========
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The MFD devices register their children as platform devices. For the child
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devices there needs to be an ACPI handle that they can use to reference
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parts of the ACPI namespace that relate to them. In the Linux MFD subsystem
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we provide two ways:
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o The children share the parent ACPI handle.
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o The MFD cell can specify the ACPI id of the device.
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- The children share the parent ACPI handle.
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- The MFD cell can specify the ACPI id of the device.
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For the first case, the MFD drivers do not need to do anything. The
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resulting child platform device will have its ACPI_COMPANION() set to point
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to the parent device.
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If the ACPI namespace has a device that we can match using an ACPI id or ACPI
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adr, the cell should be set like:
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adr, the cell should be set like::
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static struct mfd_cell_acpi_match my_subdevice_cell_acpi_match = {
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.pnpid = "XYZ0001",
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@ -366,7 +376,8 @@ the MFD device and if found, that ACPI companion device is bound to the
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resulting child platform device.
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Device Tree namespace link device ID
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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====================================
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The Device Tree protocol uses device identification based on the "compatible"
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property whose value is a string or an array of strings recognized as device
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identifiers by drivers and the driver core. The set of all those strings may be
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@ -449,4 +460,4 @@ the _DSD of the device object itself or the _DSD of its ancestor in the
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Otherwise, the _DSD itself is regarded as invalid and therefore the "compatible"
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property returned by it is meaningless.
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Refer to DSD-properties-rules.txt for more information.
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Refer to :doc:`DSD-properties-rules` for more information.
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@ -8,3 +8,4 @@ ACPI Support
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:maxdepth: 1
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namespace
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enumeration
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