[PATCH v6 08/24] Documentation: ACPI: move gpio-properties.txt to firmware-guide/acpi and convert to reST

Changbin Du
2019-04-25T15:34:43Z

.../acpi/gpio-properties.rst} | 78 +++++++++++--------
Documentation/firmware-guide/acpi/index.rst | 1 +
MAINTAINERS | 2 +-
3 files changed, 46 insertions(+), 35 deletions(-)
rename Documentation/{acpi/gpio-properties.txt => firmware-guide/acpi/gpio-properties.rst} (81%)

diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/firmware-guide/acpi/gpio-properties.rst
similarity index 81%
rename from Documentation/acpi/gpio-properties.txt
rename to Documentation/firmware-guide/acpi/gpio-properties.rst
index 88c65cb5bf0a..bb6d74f23ee0 100644
--- a/Documentation/acpi/gpio-properties.txt
+++ b/Documentation/firmware-guide/acpi/gpio-properties.rst
@@ -1,5 +1,8 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
_DSD Device Properties Related to GPIO
---------------------------------------
+======================================

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
@@ -8,7 +11,7 @@ the corresponding GPIO, which is pretty error prone (it depends on
the _CRS output ordering, for example).

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
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 }}

- ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
- typically this is the device itself (BTH in our case).
- index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
- pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
- active_low - If 1 the GPIO is marked as active_low.
+ref
+ The device that has _CRS containing GpioIo()/GpioInt() resources,
+ typically this is the device itself (BTH in our case).
+index
+ Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
+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
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
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
-native:
+native::

Package () {
"cs-gpios",
@@ -67,7 +74,7 @@ native:
}

Other supported properties
---------------------------
+==========================

Following Device Tree compatible device properties are also supported by
_DSD device properties for GPIO controllers:
@@ -78,7 +85,7 @@ _DSD device properties for GPIO controllers:
- input
- line-name

-Example:
+Example::

Name (_DSD, Package () {
// _DSD Hierarchical Properties Extension UUID
@@ -100,7 +107,7 @@ Example:

- gpio-line-names

-Example:
+Example::

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

ACPI GPIO Mappings Provided by Drivers
---------------------------------------
+======================================

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
@@ -139,16 +146,16 @@ 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.

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 shutdown_gpio = { 0, 0, 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_mapping bluetooth_acpi_gpios[] = {
- { "reset-gpios", &reset_gpio, 1 },
- { "shutdown-gpios", &shutdown_gpio, 1 },
- { },
-};
+ static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
+ { "reset-gpios", &reset_gpio, 1 },
+ { "shutdown-gpios", &shutdown_gpio, 1 },
+ { },
+ };

Next, the mapping table needs to be passed as the second argument to
acpi_dev_add_driver_gpios() that will register it with the ACPI device object
@@ -158,12 +165,12 @@ calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
table was previously registered.

Using the _CRS fallback
------------------------
+=======================

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
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)
{
@@ -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);

@@ -193,22 +200,25 @@ 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.

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_index(dev, connection_id, index, flags);
+ desc = gpiod_get(dev, connection_id, flags);
+ desc = gpiod_get_index(dev, connection_id, index, flags);

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

-Case 1:
- desc = gpiod_get(dev, "non-null-connection-id", flags);
- desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);
+Case 1::
+
+ desc = gpiod_get(dev, "non-null-connection-id", 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_index(dev, NULL, index, flags);
+ desc = gpiod_get(dev, NULL, flags);
+ desc = gpiod_get_index(dev, NULL, index, flags);

Case 1 assumes that corresponding ACPI device description must have
defined device properties and will prevent to getting any GPIO resources
diff --git a/Documentation/firmware-guide/acpi/index.rst b/Documentation/firmware-guide/acpi/index.rst
index 0e05b843521c..61d67763851b 100644
--- a/Documentation/firmware-guide/acpi/index.rst
+++ b/Documentation/firmware-guide/acpi/index.rst
@@ -11,3 +11,4 @@ ACPI Support
enumeration
osi
DSD-properties-rules
+ gpio-properties
diff --git a/MAINTAINERS b/MAINTAINERS
index 09f43f1bdd15..87f930bf32ad 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6593,7 +6593,7 @@ M: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
L: linux-gpio@vger.kernel.org
L: linux-acpi@vger.kernel.org
S: Maintained
-F: Documentation/acpi/gpio-properties.txt
+F: Documentation/firmware-guide/acpi/gpio-properties.rst
F: drivers/gpio/gpiolib-acpi.c

GPIO IR Transmitter
--
2.20.1