+.. 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
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)
})
}
-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
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",
}
Other supported properties
---------------------------
+==========================
Following Device Tree compatible device properties are also supported by
_DSD device properties for GPIO controllers:
- input
- line-name
-Example:
+Example::
Name (_DSD, Package () {
// _DSD Hierarchical Properties Extension UUID
- gpio-line-names
-Example:
+Example::
Package () {
"gpio-line-names",
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
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
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)
{
})
}
-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);
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