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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: 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
parent
538f6f76b9
commit
b6dff0e153
@ -1,5 +1,8 @@
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.. SPDX-License-Identifier: GPL-2.0
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======================================
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_DSD Device Properties Related to GPIO
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--------------------------------------
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======================================
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With the release of ACPI 5.1, the _DSD configuration object finally
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allows names to be given to GPIOs (and other things as well) returned
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@ -8,7 +11,7 @@ the corresponding GPIO, which is pretty error prone (it depends on
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the _CRS output ordering, for example).
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With _DSD we can now query GPIOs using a name instead of an integer
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index, like the ASL example below shows:
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index, like the ASL example below shows::
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// Bluetooth device with reset and shutdown GPIOs
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Device (BTH)
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@ -34,15 +37,19 @@ index, like the ASL example below shows:
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})
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}
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The format of the supported GPIO property is:
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The format of the supported GPIO property is::
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Package () { "name", Package () { ref, index, pin, active_low }}
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ref - The device that has _CRS containing GpioIo()/GpioInt() resources,
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typically this is the device itself (BTH in our case).
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index - Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
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pin - Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
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active_low - If 1 the GPIO is marked as active_low.
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ref
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The device that has _CRS containing GpioIo()/GpioInt() resources,
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typically this is the device itself (BTH in our case).
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index
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Index of the GpioIo()/GpioInt() resource in _CRS starting from zero.
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pin
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Pin in the GpioIo()/GpioInt() resource. Typically this is zero.
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active_low
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If 1 the GPIO is marked as active_low.
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Since ACPI GpioIo() resource does not have a field saying whether it is
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active low or high, the "active_low" argument can be used here. Setting
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@ -55,7 +62,7 @@ It is possible to leave holes in the array of GPIOs. This is useful in
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cases like with SPI host controllers where some chip selects may be
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implemented as GPIOs and some as native signals. For example a SPI host
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controller can have chip selects 0 and 2 implemented as GPIOs and 1 as
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native:
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native::
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Package () {
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"cs-gpios",
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@ -67,7 +74,7 @@ native:
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}
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Other supported properties
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--------------------------
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==========================
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Following Device Tree compatible device properties are also supported by
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_DSD device properties for GPIO controllers:
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@ -78,7 +85,7 @@ _DSD device properties for GPIO controllers:
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- input
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- line-name
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Example:
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Example::
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Name (_DSD, Package () {
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// _DSD Hierarchical Properties Extension UUID
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@ -100,7 +107,7 @@ Example:
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- gpio-line-names
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Example:
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Example::
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Package () {
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"gpio-line-names",
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@ -114,7 +121,7 @@ See Documentation/devicetree/bindings/gpio/gpio.txt for more information
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about these properties.
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ACPI GPIO Mappings Provided by Drivers
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--------------------------------------
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======================================
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There are systems in which the ACPI tables do not contain _DSD but provide _CRS
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with GpioIo()/GpioInt() resources and device drivers still need to work with
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@ -139,16 +146,16 @@ line in that resource starting from zero, and the active-low flag for that line,
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respectively, in analogy with the _DSD GPIO property format specified above.
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For the example Bluetooth device discussed previously the data structures in
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question would look like this:
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question would look like this::
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static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
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static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
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static const struct acpi_gpio_params reset_gpio = { 1, 1, false };
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static const struct acpi_gpio_params shutdown_gpio = { 0, 0, false };
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static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
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{ "reset-gpios", &reset_gpio, 1 },
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{ "shutdown-gpios", &shutdown_gpio, 1 },
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{ },
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};
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static const struct acpi_gpio_mapping bluetooth_acpi_gpios[] = {
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{ "reset-gpios", &reset_gpio, 1 },
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{ "shutdown-gpios", &shutdown_gpio, 1 },
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{ },
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};
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Next, the mapping table needs to be passed as the second argument to
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acpi_dev_add_driver_gpios() that will register it with the ACPI device object
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@ -158,12 +165,12 @@ calling acpi_dev_remove_driver_gpios() on the ACPI device object where that
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table was previously registered.
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Using the _CRS fallback
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-----------------------
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=======================
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If a device does not have _DSD or the driver does not create ACPI GPIO
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mapping, the Linux GPIO framework refuses to return any GPIOs. This is
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because the driver does not know what it actually gets. For example if we
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have a device like below:
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have a device like below::
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Device (BTH)
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{
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@ -177,7 +184,7 @@ have a device like below:
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})
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}
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The driver might expect to get the right GPIO when it does:
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The driver might expect to get the right GPIO when it does::
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desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);
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@ -193,22 +200,25 @@ the ACPI GPIO mapping tables are hardly linked to ACPI ID and certain
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objects, as listed in the above chapter, of the device in question.
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Getting GPIO descriptor
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-----------------------
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=======================
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There are two main approaches to get GPIO resource from ACPI:
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desc = gpiod_get(dev, connection_id, flags);
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desc = gpiod_get_index(dev, connection_id, index, flags);
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There are two main approaches to get GPIO resource from ACPI::
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desc = gpiod_get(dev, connection_id, flags);
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desc = gpiod_get_index(dev, connection_id, index, flags);
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We may consider two different cases here, i.e. when connection ID is
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provided and otherwise.
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Case 1:
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desc = gpiod_get(dev, "non-null-connection-id", flags);
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desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);
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Case 1::
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Case 2:
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desc = gpiod_get(dev, NULL, flags);
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desc = gpiod_get_index(dev, NULL, index, flags);
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desc = gpiod_get(dev, "non-null-connection-id", flags);
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desc = gpiod_get_index(dev, "non-null-connection-id", index, flags);
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Case 2::
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desc = gpiod_get(dev, NULL, flags);
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desc = gpiod_get_index(dev, NULL, index, flags);
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Case 1 assumes that corresponding ACPI device description must have
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defined device properties and will prevent to getting any GPIO resources
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@ -11,3 +11,4 @@ ACPI Support
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enumeration
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osi
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DSD-properties-rules
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gpio-properties
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@ -6593,7 +6593,7 @@ M: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
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L: linux-gpio@vger.kernel.org
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L: linux-acpi@vger.kernel.org
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S: Maintained
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F: Documentation/acpi/gpio-properties.txt
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F: Documentation/firmware-guide/acpi/gpio-properties.rst
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F: drivers/gpio/gpiolib-acpi.c
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GPIO IR Transmitter
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