--- /dev/null
+=============
+GPIO Mappings
+=============
+
+This document explains how GPIOs can be assigned to given devices and functions.
+
+Note that it only applies to the new descriptor-based interface. For a
+description of the deprecated integer-based GPIO interface please refer to
+gpio-legacy.txt (actually, there is no real mapping possible with the old
+interface; you just fetch an integer from somewhere and request the
+corresponding GPIO).
+
+All platforms can enable the GPIO library, but if the platform strictly
+requires GPIO functionality to be present, it needs to select GPIOLIB from its
+Kconfig. Then, how GPIOs are mapped depends on what the platform uses to
+describe its hardware layout. Currently, mappings can be defined through device
+tree, ACPI, and platform data.
+
+Device Tree
+-----------
+GPIOs can easily be mapped to devices and functions in the device tree. The
+exact way to do it depends on the GPIO controller providing the GPIOs, see the
+device tree bindings for your controller.
+
+GPIOs mappings are defined in the consumer device's node, in a property named
+<function>-gpios, where <function> is the function the driver will request
+through gpiod_get(). For example::
+
+ foo_device {
+ compatible = "acme,foo";
+ ...
+ led-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
+ <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
+ <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
+
+ power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
+ };
+
+Properties named <function>-gpio are also considered valid and old bindings use
+it but are only supported for compatibility reasons and should not be used for
+newer bindings since it has been deprecated.
+
+This property will make GPIOs 15, 16 and 17 available to the driver under the
+"led" function, and GPIO 1 as the "power" GPIO::
+
+ struct gpio_desc *red, *green, *blue, *power;
+
+ red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
+ green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
+ blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
+
+ power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
+
+The led GPIOs will be active high, while the power GPIO will be active low (i.e.
+gpiod_is_active_low(power) will be true).
+
+The second parameter of the gpiod_get() functions, the con_id string, has to be
+the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
+looked up by the gpiod functions internally) used in the device tree. With above
+"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
+
+Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
+with the string passed in con_id to get the resulting string
+(``snprintf(... "%s-%s", con_id, gpio_suffixes[]``).
+
+ACPI
+----
+ACPI also supports function names for GPIOs in a similar fashion to DT.
+The above DT example can be converted to an equivalent ACPI description
+with the help of _DSD (Device Specific Data), introduced in ACPI 5.1::
+
+ Device (FOO) {
+ Name (_CRS, ResourceTemplate () {
+ GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+ "\\_SB.GPI0") {15} // red
+ GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+ "\\_SB.GPI0") {16} // green
+ GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+ "\\_SB.GPI0") {17} // blue
+ GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
+ "\\_SB.GPI0") {1} // power
+ })
+
+ Name (_DSD, Package () {
+ ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+ Package () {
+ Package () {
+ "led-gpios",
+ Package () {
+ ^FOO, 0, 0, 1,
+ ^FOO, 1, 0, 1,
+ ^FOO, 2, 0, 1,
+ }
+ },
+ Package () {
+ "power-gpios",
+ Package () {^FOO, 3, 0, 0},
+ },
+ }
+ })
+ }
+
+For more information about the ACPI GPIO bindings see
+Documentation/acpi/gpio-properties.txt.
+
+Platform Data
+-------------
+Finally, GPIOs can be bound to devices and functions using platform data. Board
+files that desire to do so need to include the following header::
+
+ #include <linux/gpio/machine.h>
+
+GPIOs are mapped by the means of tables of lookups, containing instances of the
+gpiod_lookup structure. Two macros are defined to help declaring such mappings::
+
+ GPIO_LOOKUP(chip_label, chip_hwnum, con_id, flags)
+ GPIO_LOOKUP_IDX(chip_label, chip_hwnum, con_id, idx, flags)
+
+where
+
+ - chip_label is the label of the gpiod_chip instance providing the GPIO
+ - chip_hwnum is the hardware number of the GPIO within the chip
+ - con_id is the name of the GPIO function from the device point of view. It
+ can be NULL, in which case it will match any function.
+ - idx is the index of the GPIO within the function.
+ - flags is defined to specify the following properties:
+ * GPIO_ACTIVE_HIGH - GPIO line is active high
+ * GPIO_ACTIVE_LOW - GPIO line is active low
+ * GPIO_OPEN_DRAIN - GPIO line is set up as open drain
+ * GPIO_OPEN_SOURCE - GPIO line is set up as open source
+ * GPIO_PERSISTENT - GPIO line is persistent during
+ suspend/resume and maintains its value
+ * GPIO_TRANSITORY - GPIO line is transitory and may loose its
+ electrical state during suspend/resume
+
+In the future, these flags might be extended to support more properties.
+
+Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
+
+A lookup table can then be defined as follows, with an empty entry defining its
+end. The 'dev_id' field of the table is the identifier of the device that will
+make use of these GPIOs. It can be NULL, in which case it will be matched for
+calls to gpiod_get() with a NULL device.
+
+.. code-block:: c
+
+ struct gpiod_lookup_table gpios_table = {
+ .dev_id = "foo.0",
+ .table = {
+ GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
+ GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
+ GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
+ GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
+ { },
+ },
+ };
+
+And the table can be added by the board code as follows::
+
+ gpiod_add_lookup_table(&gpios_table);
+
+The driver controlling "foo.0" will then be able to obtain its GPIOs as follows::
+
+ struct gpio_desc *red, *green, *blue, *power;
+
+ red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
+ green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
+ blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
+
+ power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
+
+Since the "led" GPIOs are mapped as active-high, this example will switch their
+signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
+as active-low, its actual signal will be 0 after this code. Contrary to the
+legacy integer GPIO interface, the active-low property is handled during
+mapping and is thus transparent to GPIO consumers.
+
+A set of functions such as gpiod_set_value() is available to work with
+the new descriptor-oriented interface.
+++ /dev/null
-GPIO Mappings
-=============
-
-This document explains how GPIOs can be assigned to given devices and functions.
-
-Note that it only applies to the new descriptor-based interface. For a
-description of the deprecated integer-based GPIO interface please refer to
-gpio-legacy.txt (actually, there is no real mapping possible with the old
-interface; you just fetch an integer from somewhere and request the
-corresponding GPIO).
-
-All platforms can enable the GPIO library, but if the platform strictly
-requires GPIO functionality to be present, it needs to select GPIOLIB from its
-Kconfig. Then, how GPIOs are mapped depends on what the platform uses to
-describe its hardware layout. Currently, mappings can be defined through device
-tree, ACPI, and platform data.
-
-Device Tree
------------
-GPIOs can easily be mapped to devices and functions in the device tree. The
-exact way to do it depends on the GPIO controller providing the GPIOs, see the
-device tree bindings for your controller.
-
-GPIOs mappings are defined in the consumer device's node, in a property named
-<function>-gpios, where <function> is the function the driver will request
-through gpiod_get(). For example:
-
- foo_device {
- compatible = "acme,foo";
- ...
- led-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
- <&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
- <&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
-
- power-gpios = <&gpio 1 GPIO_ACTIVE_LOW>;
- };
-
-Properties named <function>-gpio are also considered valid and old bindings use
-it but are only supported for compatibility reasons and should not be used for
-newer bindings since it has been deprecated.
-
-This property will make GPIOs 15, 16 and 17 available to the driver under the
-"led" function, and GPIO 1 as the "power" GPIO:
-
- struct gpio_desc *red, *green, *blue, *power;
-
- red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
- green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
- blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
-
- power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
-
-The led GPIOs will be active high, while the power GPIO will be active low (i.e.
-gpiod_is_active_low(power) will be true).
-
-The second parameter of the gpiod_get() functions, the con_id string, has to be
-the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
-looked up by the gpiod functions internally) used in the device tree. With above
-"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
-
-Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
-with the string passed in con_id to get the resulting string
-(snprintf(... "%s-%s", con_id, gpio_suffixes[]).
-
-ACPI
-----
-ACPI also supports function names for GPIOs in a similar fashion to DT.
-The above DT example can be converted to an equivalent ACPI description
-with the help of _DSD (Device Specific Data), introduced in ACPI 5.1:
-
- Device (FOO) {
- Name (_CRS, ResourceTemplate () {
- GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
- "\\_SB.GPI0") {15} // red
- GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
- "\\_SB.GPI0") {16} // green
- GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
- "\\_SB.GPI0") {17} // blue
- GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
- "\\_SB.GPI0") {1} // power
- })
-
- Name (_DSD, Package () {
- ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
- Package () {
- Package () {
- "led-gpios",
- Package () {
- ^FOO, 0, 0, 1,
- ^FOO, 1, 0, 1,
- ^FOO, 2, 0, 1,
- }
- },
- Package () {
- "power-gpios",
- Package () {^FOO, 3, 0, 0},
- },
- }
- })
- }
-
-For more information about the ACPI GPIO bindings see
-Documentation/acpi/gpio-properties.txt.
-
-Platform Data
--------------
-Finally, GPIOs can be bound to devices and functions using platform data. Board
-files that desire to do so need to include the following header:
-
- #include <linux/gpio/machine.h>
-
-GPIOs are mapped by the means of tables of lookups, containing instances of the
-gpiod_lookup structure. Two macros are defined to help declaring such mappings:
-
- GPIO_LOOKUP(chip_label, chip_hwnum, con_id, flags)
- GPIO_LOOKUP_IDX(chip_label, chip_hwnum, con_id, idx, flags)
-
-where
-
- - chip_label is the label of the gpiod_chip instance providing the GPIO
- - chip_hwnum is the hardware number of the GPIO within the chip
- - con_id is the name of the GPIO function from the device point of view. It
- can be NULL, in which case it will match any function.
- - idx is the index of the GPIO within the function.
- - flags is defined to specify the following properties:
- * GPIO_ACTIVE_HIGH - GPIO line is active high
- * GPIO_ACTIVE_LOW - GPIO line is active low
- * GPIO_OPEN_DRAIN - GPIO line is set up as open drain
- * GPIO_OPEN_SOURCE - GPIO line is set up as open source
- * GPIO_PERSISTENT - GPIO line is persistent during
- suspend/resume and maintains its value
- * GPIO_TRANSITORY - GPIO line is transitory and may loose its
- electrical state during suspend/resume
-
-In the future, these flags might be extended to support more properties.
-
-Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
-
-A lookup table can then be defined as follows, with an empty entry defining its
-end. The 'dev_id' field of the table is the identifier of the device that will
-make use of these GPIOs. It can be NULL, in which case it will be matched for
-calls to gpiod_get() with a NULL device.
-
-struct gpiod_lookup_table gpios_table = {
- .dev_id = "foo.0",
- .table = {
- GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
- GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
- GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
- GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
- { },
- },
-};
-
-And the table can be added by the board code as follows:
-
- gpiod_add_lookup_table(&gpios_table);
-
-The driver controlling "foo.0" will then be able to obtain its GPIOs as follows:
-
- struct gpio_desc *red, *green, *blue, *power;
-
- red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
- green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
- blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
-
- power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
-
-Since the "led" GPIOs are mapped as active-high, this example will switch their
-signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
-as active-low, its actual signal will be 0 after this code. Contrary to the
-legacy integer GPIO interface, the active-low property is handled during
-mapping and is thus transparent to GPIO consumers.
-
-A set of functions such as gpiod_set_value() is available to work with
-the new descriptor-oriented interface.
projects / linux.git / commitdiff