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>

1 files changed, 0 insertions, 223 deletions

diff --git a/Documentation/acpi/gpio-properties.txt b/Documentation/acpi/gpio-properties.txt
deleted file mode 100644
index 88c65cb5bf0a..000000000000
--- a/Documentation/acpi/gpio-properties.txt
+++ /dev/null
@@ -1,223 +0,0 @@
-_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
-by _CRS.  Previously, we were only able to use an integer index to find
-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:
-
-  // Bluetooth device with reset and shutdown GPIOs
-  Device (BTH)
-  {
-      Name (_HID, ...)
-
-      Name (_CRS, ResourceTemplate ()
-      {
-          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
-                  "\\_SB.GPO0", 0, ResourceConsumer) {15}
-          GpioIo (Exclusive, PullUp, 0, 0, IoRestrictionInputOnly,
-                  "\\_SB.GPO0", 0, ResourceConsumer) {27, 31}
-      })
-
-      Name (_DSD, Package ()
-      {
-          ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
-          Package ()
-	  {
-              Package () {"reset-gpios", Package() {^BTH, 1, 1, 0 }},
-              Package () {"shutdown-gpios", Package() {^BTH, 0, 0, 0 }},
-          }
-      })
-  }
-
-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.
-
-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
-it to 1 marks the GPIO as active low.
-
-In our Bluetooth example the "reset-gpios" refers to the second GpioIo()
-resource, second pin in that resource with the GPIO number of 31.
-
-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:
-
-  Package () {
-      "cs-gpios",
-      Package () {
-          ^GPIO, 19, 0, 0, // chip select 0: GPIO
-          0,               // chip select 1: native signal
-          ^GPIO, 20, 0, 0, // chip select 2: GPIO
-      }
-  }
-
-Other supported properties
---------------------------
-
-Following Device Tree compatible device properties are also supported by
-_DSD device properties for GPIO controllers:
-
-- gpio-hog
-- output-high
-- output-low
-- input
-- line-name
-
-Example:
-
-  Name (_DSD, Package () {
-      // _DSD Hierarchical Properties Extension UUID
-      ToUUID("dbb8e3e6-5886-4ba6-8795-1319f52a966b"),
-      Package () {
-          Package () {"hog-gpio8", "G8PU"}
-      }
-  })
-
-  Name (G8PU, Package () {
-      ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
-      Package () {
-          Package () {"gpio-hog", 1},
-          Package () {"gpios", Package () {8, 0}},
-          Package () {"output-high", 1},
-          Package () {"line-name", "gpio8-pullup"},
-      }
-  })
-
-- gpio-line-names
-
-Example:
-
-  Package () {
-      "gpio-line-names",
-      Package () {
-          "SPI0_CS_N", "EXP2_INT", "MUX6_IO", "UART0_RXD", "MUX7_IO",
-          "LVL_C_A1", "MUX0_IO", "SPI1_MISO"
-      }
-  }
-
-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
-them.
-
-In those cases ACPI device identification objects, _HID, _CID, _CLS, _SUB, _HRV,
-available to the driver can be used to identify the device and that is supposed
-to be sufficient to determine the meaning and purpose of all of the GPIO lines
-listed by the GpioIo()/GpioInt() resources returned by _CRS.  In other words,
-the driver is supposed to know what to use the GpioIo()/GpioInt() resources for
-once it has identified the device.  Having done that, it can simply assign names
-to the GPIO lines it is going to use and provide the GPIO subsystem with a
-mapping between those names and the ACPI GPIO resources corresponding to them.
-
-To do that, the driver needs to define a mapping table as a NULL-terminated
-array of struct acpi_gpio_mapping objects that each contain a name, a pointer
-to an array of line data (struct acpi_gpio_params) objects and the size of that
-array.  Each struct acpi_gpio_params object consists of three fields,
-crs_entry_index, line_index, active_low, representing the index of the target
-GpioIo()/GpioInt() resource in _CRS starting from zero, the index of the target
-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:
-
-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 },
-  { },
-};
-
-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
-pointed to by its first argument.  That should be done in the driver's .probe()
-routine.  On removal, the driver should unregister its GPIO mapping table by
-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:
-
-  Device (BTH)
-  {
-      Name (_HID, ...)
-
-      Name (_CRS, ResourceTemplate () {
-          GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
-                  "\\_SB.GPO0", 0, ResourceConsumer) {15}
-          GpioIo (Exclusive, PullNone, 0, 0, IoRestrictionNone,
-                  "\\_SB.GPO0", 0, ResourceConsumer) {27}
-      })
-  }
-
-The driver might expect to get the right GPIO when it does:
-
-  desc = gpiod_get(dev, "reset", GPIOD_OUT_LOW);
-
-but since there is no way to know the mapping between "reset" and
-the GpioIo() in _CRS desc will hold ERR_PTR(-ENOENT).
-
-The driver author can solve this by passing the mapping explictly
-(the recommended way and documented in the above chapter).
-
-The ACPI GPIO mapping tables should not contaminate drivers that are not
-knowing about which exact device they are servicing on. It implies that
-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:
-	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 2:
-	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
-otherwise.
-
-Case 2 explicitly tells GPIO core to look for resources in _CRS.
-
-Be aware that gpiod_get_index() in cases 1 and 2, assuming that there
-are two versions of ACPI device description provided and no mapping is
-present in the driver, will return different resources. That's why a
-certain driver has to handle them carefully as explained in previous
-chapter.