[mirror_ubuntu-zesty-kernel.git] / Documentation / gpio / board.txt

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.

Platforms that make use of GPIOs must select ARCH_REQUIRE_GPIOLIB (if GPIO usage
is mandatory) or ARCH_WANT_OPTIONAL_GPIOLIB (if GPIO support can be omitted) in
their 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
either <function>-gpios or <function>-gpio, 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-gpio = <&gpio 1 GPIO_ACTIVE_LOW>;
	};

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, dev_id, con_id, flags)
	GPIO_LOOKUP_IDX(chip_label, chip_hwnum, dev_id, 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
  - dev_id is the identifier of the device that will make use of this GPIO. It
	can be NULL, in which case it will be matched for calls to gpiod_get()
	with a NULL device.
  - 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:
	* GPIOF_ACTIVE_LOW	- to configure the GPIO as active-low
	* GPIOF_OPEN_DRAIN	- GPIO pin is open drain type.
	* GPIOF_OPEN_SOURCE	- GPIO pin is open source type.

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:

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.
Commit	Line	Data
fd8e198c AC	1	GPIO Mappings
	2	=============
	3
	4	This document explains how GPIOs can be assigned to given devices and functions.
	5	Note that it only applies to the new descriptor-based interface. For a
	6	description of the deprecated integer-based GPIO interface please refer to
	7	gpio-legacy.txt (actually, there is no real mapping possible with the old
	8	interface; you just fetch an integer from somewhere and request the
	9	corresponding GPIO.
	10
	11	Platforms that make use of GPIOs must select ARCH_REQUIRE_GPIOLIB (if GPIO usage
	12	is mandatory) or ARCH_WANT_OPTIONAL_GPIOLIB (if GPIO support can be omitted) in
	13	their Kconfig. Then, how GPIOs are mapped depends on what the platform uses to
	14	describe its hardware layout. Currently, mappings can be defined through device
	15	tree, ACPI, and platform data.
	16
	17	Device Tree
	18	-----------
	19	GPIOs can easily be mapped to devices and functions in the device tree. The
	20	exact way to do it depends on the GPIO controller providing the GPIOs, see the
	21	device tree bindings for your controller.
	22
	23	GPIOs mappings are defined in the consumer device's node, in a property named
ae80d64e JMC	24	either <function>-gpios or <function>-gpio, where <function> is the function
ae80d64e JMC	25	the driver will request through gpiod_get(). For example:
fd8e198c AC	26
	27	foo_device {
	28	compatible = "acme,foo";
	29	...
	30	led-gpios = <&gpio 15 GPIO_ACTIVE_HIGH>, /* red */
	31	<&gpio 16 GPIO_ACTIVE_HIGH>, /* green */
	32	<&gpio 17 GPIO_ACTIVE_HIGH>; /* blue */
	33
ae80d64e	34	power-gpio = <&gpio 1 GPIO_ACTIVE_LOW>;
fd8e198c AC	35	};
	36
	37	This property will make GPIOs 15, 16 and 17 available to the driver under the
	38	"led" function, and GPIO 1 as the "power" GPIO:
	39
	40	struct gpio_desc red, green, blue, power;
	41
69de52ba DB	42	red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
	43	green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
	44	blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
fd8e198c	45
69de52ba	46	power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
fd8e198c AC	47
	48	The led GPIOs will be active-high, while the power GPIO will be active-low (i.e.
	49	gpiod_is_active_low(power) will be true).
	50
87e77e46 DB	51	The second parameter of the gpiod_get() functions, the con_id string, has to be
	52	the <function>-prefix of the GPIO suffixes ("gpios" or "gpio", automatically
	53	looked up by the gpiod functions internally) used in the device tree. With above
	54	"led-gpios" example, use the prefix without the "-" as con_id parameter: "led".
	55
	56	Internally, the GPIO subsystem prefixes the GPIO suffix ("gpios" or "gpio")
	57	with the string passed in con_id to get the resulting string
	58	(snprintf(... "%s-%s", con_id, gpio_suffixes[]).
	59
fd8e198c AC	60	ACPI
fd8e198c AC	61	----
cfc50764 MW	62	ACPI also supports function names for GPIOs in a similar fashion to DT.
	63	The above DT example can be converted to an equivalent ACPI description
	64	with the help of _DSD (Device Specific Data), introduced in ACPI 5.1:
	65
	66	Device (FOO) {
	67	Name (_CRS, ResourceTemplate () {
	68	GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
	69	"\\_SB.GPI0") {15} // red
	70	GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
	71	"\\_SB.GPI0") {16} // green
	72	GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
	73	"\\_SB.GPI0") {17} // blue
	74	GpioIo (Exclusive, ..., IoRestrictionOutputOnly,
	75	"\\_SB.GPI0") {1} // power
	76	})
	77
	78	Name (_DSD, Package () {
	79	ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
	80	Package () {
	81	Package () {
	82	"led-gpios",
	83	Package () {
	84	^FOO, 0, 0, 1,
	85	^FOO, 1, 0, 1,
	86	^FOO, 2, 0, 1,
	87	}
	88	},
	89	Package () {
	90	"power-gpios",
	91	Package () {^FOO, 3, 0, 0},
	92	},
	93	}
	94	})
	95	}
	96
	97	For more information about the ACPI GPIO bindings see
	98	Documentation/acpi/gpio-properties.txt.
fd8e198c AC	99
	100	Platform Data
	101	-------------
	102	Finally, GPIOs can be bound to devices and functions using platform data. Board
	103	files that desire to do so need to include the following header:
	104
0a6d3158	105	#include <linux/gpio/machine.h>
fd8e198c AC	106
	107	GPIOs are mapped by the means of tables of lookups, containing instances of the
	108	gpiod_lookup structure. Two macros are defined to help declaring such mappings:
	109
	110	GPIO_LOOKUP(chip_label, chip_hwnum, dev_id, con_id, flags)
	111	GPIO_LOOKUP_IDX(chip_label, chip_hwnum, dev_id, con_id, idx, flags)
	112
	113	where
	114
	115	- chip_label is the label of the gpiod_chip instance providing the GPIO
	116	- chip_hwnum is the hardware number of the GPIO within the chip
ad824783 AC	117	- dev_id is the identifier of the device that will make use of this GPIO. It
	118	can be NULL, in which case it will be matched for calls to gpiod_get()
	119	with a NULL device.
fd8e198c	120	- con_id is the name of the GPIO function from the device point of view. It
ad824783	121	can be NULL, in which case it will match any function.
fd8e198c AC	122	- idx is the index of the GPIO within the function.
	123	- flags is defined to specify the following properties:
	124	* GPIOF_ACTIVE_LOW - to configure the GPIO as active-low
	125	* GPIOF_OPEN_DRAIN - GPIO pin is open drain type.
	126	* GPIOF_OPEN_SOURCE - GPIO pin is open source type.
	127
	128	In the future, these flags might be extended to support more properties.
	129
	130	Note that GPIO_LOOKUP() is just a shortcut to GPIO_LOOKUP_IDX() where idx = 0.
	131
ad824783 AC	132	A lookup table can then be defined as follows, with an empty entry defining its
ad824783 AC	133	end:
fd8e198c	134
ad824783 AC	135	struct gpiod_lookup_table gpios_table = {
	136	.dev_id = "foo.0",
	137	.table = {
	138	GPIO_LOOKUP_IDX("gpio.0", 15, "led", 0, GPIO_ACTIVE_HIGH),
	139	GPIO_LOOKUP_IDX("gpio.0", 16, "led", 1, GPIO_ACTIVE_HIGH),
	140	GPIO_LOOKUP_IDX("gpio.0", 17, "led", 2, GPIO_ACTIVE_HIGH),
	141	GPIO_LOOKUP("gpio.0", 1, "power", GPIO_ACTIVE_LOW),
	142	{ },
	143	},
	144	};
fd8e198c AC	145
	146	And the table can be added by the board code as follows:
	147
ad824783	148	gpiod_add_lookup_table(&gpios_table);
fd8e198c AC	149
	150	The driver controlling "foo.0" will then be able to obtain its GPIOs as follows:
	151
	152	struct gpio_desc red, green, blue, power;
	153
69de52ba DB	154	red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_HIGH);
	155	green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_HIGH);
	156	blue = gpiod_get_index(dev, "led", 2, GPIOD_OUT_HIGH);
fd8e198c	157
69de52ba	158	power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
fd8e198c	159
69de52ba DB	160	Since the "led" GPIOs are mapped as active-high, this example will switch their
	161	signals to 1, i.e. enabling the LEDs. And for the "power" GPIO, which is mapped
	162	as active-low, its actual signal will be 0 after this code. Contrary to the legacy
	163	integer GPIO interface, the active-low property is handled during mapping and is
	164	thus transparent to GPIO consumers.