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Based on kernel version 4.3. Page generated on 2015-11-02 12:49 EST.

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
24	either <function>-gpios or <function>-gpio, where <function> is the function
25	the driver will request through gpiod_get(). For example:
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	
34			power-gpio = <&gpio 1 GPIO_ACTIVE_LOW>;
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	
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);
45	
46		power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
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	
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	
60	ACPI
61	----
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.
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	
105		#include <linux/gpio/machine.h>
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
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.
120	  - con_id is the name of the GPIO function from the device point of view. It
121		can be NULL, in which case it will match any function.
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	
132	A lookup table can then be defined as follows, with an empty entry defining its
133	end:
134	
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	};
145	
146	And the table can be added by the board code as follows:
147	
148		gpiod_add_lookup_table(&gpios_table);
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	
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);
157	
158		power = gpiod_get(dev, "power", GPIOD_OUT_HIGH);
159	
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.
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