Commit b6dff0e1 authored by Changbin Du's avatar Changbin Du Committed by Rafael J. Wysocki
Browse files

Documentation: ACPI: move gpio-properties.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: default avatarChangbin Du <changbin.du@gmail.com>
Reviewed-by: default avatarMauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 538f6f76

Documentation/acpi/gpio-properties.txt→Documentation/firmware-guide/acpi/gpio-properties.rst

+44 −34
Original line number Original line Diff line number Diff line 
.. SPDX-License-Identifier: GPL-2.0



======================================

_DSD Device Properties Related to GPIO

_DSD Device Properties Related to GPIO

--------------------------------------

======================================





With the release of ACPI 5.1, the _DSD configuration object finally

With the release of ACPI 5.1, the _DSD configuration object finally

allows names to be given to GPIOs (and other things as well) returned

allows names to be given to GPIOs (and other things as well) returned
@@ -8,7 +11,7 @@ the corresponding GPIO, which is pretty error prone (it depends on 
the _CRS output ordering, for example).

the _CRS output ordering, for example).





With _DSD we can now query GPIOs using a name instead of an integer

With _DSD we can now query GPIOs using a name instead of an integer

index, like the ASL example below shows:

index, like the ASL example below shows::





  // Bluetooth device with reset and shutdown GPIOs

  // Bluetooth device with reset and shutdown GPIOs

  Device (BTH)

  Device (BTH)
@@ -34,15 +37,19 @@ index, like the ASL example below shows: 
      })

      })

  }

  }





The format of the supported GPIO property is:

The format of the supported GPIO property is::





  Package () { "name", Package () { ref, index, pin, active_low }}

  Package () { "name", Package () { ref, index, pin, active_low }}





  ref - The device that has _CRS containing GpioIo()/GpioInt() resources,

ref

  The device that has _CRS containing GpioIo()/GpioInt() resources,

  typically this is the device itself (BTH in our case).

  typically this is the device itself (BTH in our case).

  index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.

index

  pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.

  Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.

  active_low - If 1 the GPIO is marked as active_low.

pin

  Pin in the GpioIo()/GpioInt() resource. Typically this is zero.

active_low

  If 1 the GPIO is marked as active_low.





Since ACPI GpioIo() resource does not have a field saying whether it is

Since ACPI GpioIo() resource does not have a field saying whether it is

active low or high, the "active_low" argument can be used here.  Setting

active low or high, the "active_low" argument can be used here.  Setting
@@ -55,7 +62,7 @@ It is possible to leave holes in the array of GPIOs. This is useful in 
cases like with SPI host controllers where some chip selects may be

cases like with SPI host controllers where some chip selects may be

implemented as GPIOs and some as native signals. For example a SPI host

implemented as GPIOs and some as native signals. For example a SPI host

controller can have chip selects 0 and 2 implemented as GPIOs and 1 as

controller can have chip selects 0 and 2 implemented as GPIOs and 1 as

native:

native::





  Package () {

  Package () {

      "cs-gpios",

      "cs-gpios",
@@ -67,7 +74,7 @@ native: 
  }

  }





Other supported properties

Other supported properties

--------------------------

==========================





Following Device Tree compatible device properties are also supported by

Following Device Tree compatible device properties are also supported by

_DSD device properties for GPIO controllers:

_DSD device properties for GPIO controllers:
@@ -78,7 +85,7 @@ _DSD device properties for GPIO controllers: 
- input

- input

- line-name

- line-name





Example:

Example::





  Name (_DSD, Package () {

  Name (_DSD, Package () {

      // _DSD Hierarchical Properties Extension UUID

      // _DSD Hierarchical Properties Extension UUID
@@ -100,7 +107,7 @@ Example: 




- gpio-line-names

- gpio-line-names





Example:

Example::





  Package () {

  Package () {

      "gpio-line-names",

      "gpio-line-names",
@@ -114,7 +121,7 @@ See Documentation/devicetree/bindings/gpio/gpio.txt for more information 
about these properties.

about these properties.





ACPI GPIO Mappings Provided by Drivers

ACPI GPIO Mappings Provided by Drivers

--------------------------------------

======================================





There are systems in which the ACPI tables do not contain _DSD but provide _CRS

There are systems in which the ACPI tables do not contain _DSD but provide _CRS

with GpioIo()/GpioInt() resources and device drivers still need to work with

with GpioIo()/GpioInt() resources and device drivers still need to work with
@@ -139,7 +146,7 @@ line in that resource starting from zero, and the active-low flag for that line, 
respectively, in analogy with the _DSD GPIO property format specified above.

respectively, in analogy with the _DSD GPIO property format specified above.





For the example Bluetooth device discussed previously the data structures in

For the example Bluetooth device discussed previously the data structures in

question would look like this:

question would look like this::





  static const struct acpi_gpio_params reset_gpio = { 1, 1, false };

  static const struct acpi_gpio_params reset_gpio = { 1, 1, false };

  static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };

  static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
@@ -158,12 +165,12 @@ calling acpi_dev_remove_driver_gpios() on the ACPI device object where that 
table was previously registered.

table was previously registered.





Using the _CRS fallback

Using the _CRS fallback

-----------------------

=======================





If a device does not have _DSD or the driver does not create ACPI GPIO

If a device does not have _DSD or the driver does not create ACPI GPIO

mapping, the Linux GPIO framework refuses to return any GPIOs. This is

mapping, the Linux GPIO framework refuses to return any GPIOs. This is

because the driver does not know what it actually gets. For example if we

because the driver does not know what it actually gets. For example if we

have a device like below:

have a device like below::





  Device (BTH)

  Device (BTH)

  {

  {
@@ -177,7 +184,7 @@ have a device like below: 
      })

      })

  }

  }





The driver might expect to get the right GPIO when it does:

The driver might expect to get the right GPIO when it does::





  desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);

  desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);
@@ -193,20 +200,23 @@ the ACPI GPIO mapping tables are hardly linked to ACPI ID and certain 
objects, as listed in the above chapter, of the device in question.

objects, as listed in the above chapter, of the device in question.





Getting GPIO descriptor

Getting GPIO descriptor

-----------------------

=======================



There are two main approaches to get GPIO resource from ACPI::





There are two main approaches to get GPIO resource from ACPI:

  desc = gpiod_get(dev, connection_id, flags);

  desc = gpiod_get(dev, connection_id, flags);

  desc = gpiod_get_index(dev, connection_id, index, flags);

  desc = gpiod_get_index(dev, connection_id, index, flags);





We may consider two different cases here, i.e. when connection ID is

We may consider two different cases here, i.e. when connection ID is

provided and otherwise.

provided and otherwise.





Case 1:

Case 1::



  desc = gpiod_get(dev, "non-null-connection-id", flags);

  desc = gpiod_get(dev, "non-null-connection-id", flags);

  desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);

  desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);





Case 2:

Case 2::



  desc = gpiod_get(dev, NULL, flags);

  desc = gpiod_get(dev, NULL, flags);

  desc = gpiod_get_index(dev, NULL, index, flags);

  desc = gpiod_get_index(dev, NULL, index, flags);

Documentation/firmware-guide/acpi/index.rst

+1 −0
Original line number Original line Diff line number Diff line
@@ -11,3 +11,4 @@ ACPI Support 
   enumeration

   enumeration

   osi

   osi

   DSD-properties-rules

   DSD-properties-rules

   gpio-properties

MAINTAINERS

+1 −1
Original line number Original line Diff line number Diff line
@@ -6593,7 +6593,7 @@ M: Andy Shevchenko <andriy.shevchenko@linux.intel.com> 
L:	linux-gpio@vger.kernel.org

L:	linux-gpio@vger.kernel.org

L:	linux-acpi@vger.kernel.org

L:	linux-acpi@vger.kernel.org

S:	Maintained

S:	Maintained

F:	Documentation/acpi/gpio-properties.txt

F:	Documentation/firmware-guide/acpi/gpio-properties.rst

F:	drivers/gpio/gpiolib-acpi.c

F:	drivers/gpio/gpiolib-acpi.c





GPIO IR Transmitter

GPIO IR Transmitter

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