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Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +01001==================================
Alexandre Courbotfd8e1982013-11-16 21:34:21 +09002GPIO Descriptor Consumer Interface
3==================================
4
5This document describes the consumer interface of the GPIO framework. Note that
6it describes the new descriptor-based interface. For a description of the
7deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
8
9
10Guidelines for GPIOs consumers
11==============================
12
13Drivers that can't work without standard GPIO calls should have Kconfig entries
Linus Walleija621c992017-09-12 09:32:34 +020014that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
Jonathan Neuschäfer3fd19d42021-03-03 21:34:43 +010015obtain and use GPIOs are available by including the following file::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090016
17 #include <linux/gpio/consumer.h>
18
Linus Walleija621c992017-09-12 09:32:34 +020019There are static inline stubs for all functions in the header file in the case
20where GPIOLIB is disabled. When these stubs are called they will emit
21warnings. These stubs are used for two use cases:
22
23- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
24 the current platform does not enable or select GPIOLIB because we are not
25 going to execute the system anyway.
26
27- Truly optional GPIOLIB support - where the driver does not really make use
28 of the GPIOs on certain compile-time configurations for certain systems, but
29 will use it under other compile-time configurations. In this case the
30 consumer must make sure not to call into these functions, or the user will
31 be met with console warnings that may be perceived as intimidating.
32
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090033All the functions that work with the descriptor-based GPIO interface are
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +010034prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
35interface. No other function in the kernel should use these prefixes. The use
36of the legacy functions is strongly discouraged, new code should use
37<linux/gpio/consumer.h> and descriptors exclusively.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090038
39
40Obtaining and Disposing GPIOs
41=============================
42
43With the descriptor-based interface, GPIOs are identified with an opaque,
44non-forgeable handler that must be obtained through a call to one of the
45gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
46device that will use the GPIO and the function the requested GPIO is supposed to
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +010047fulfill::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090048
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090049 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
50 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090051
52If a function is implemented by using several GPIOs together (e.g. a simple LED
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +010053device that displays digits), an additional index argument can be specified::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090054
55 struct gpio_desc *gpiod_get_index(struct device *dev,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090056 const char *con_id, unsigned int idx,
57 enum gpiod_flags flags)
58
Dirk Behme87e77e42015-09-02 20:07:10 +020059For a more detailed description of the con_id parameter in the DeviceTree case
Mauro Carvalho Chehab5fb94e92018-05-08 15:14:57 -030060see Documentation/driver-api/gpio/board.rst
Dirk Behme87e77e42015-09-02 20:07:10 +020061
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090062The flags parameter is used to optionally specify a direction and initial value
63for the GPIO. Values can be:
64
65* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
66 later with one of the dedicated functions.
67* GPIOD_IN to initialize the GPIO as input.
68* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
69* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
Linus Walleijadbf0292018-01-18 10:43:43 +010070* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
71 to be electrically used with open drain.
72* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
73 to be electrically used with open drain.
74
Hannu Hartikainenf3f10172021-07-08 18:20:54 +030075Note that the initial value is *logical* and the physical line level depends on
76whether the line is configured active high or active low (see
77:ref:`active_low_semantics`).
78
Linus Walleijadbf0292018-01-18 10:43:43 +010079The two last flags are used for use cases where open drain is mandatory, such
80as I2C: if the line is not already configured as open drain in the mappings
81(see board.txt), then open drain will be enforced anyway and a warning will be
82printed that the board configuration needs to be updated to match the use case.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090083
84Both functions return either a valid GPIO descriptor, or an error code checkable
Alexandre Courbot2a3cf6a2013-12-11 11:32:28 +090085with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
86if and only if no GPIO has been assigned to the device/function/index triplet,
87other error codes are used for cases where a GPIO has been assigned but an error
Carlos Garciac98be0c2014-04-04 22:31:00 -040088occurred while trying to acquire it. This is useful to discriminate between mere
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070089errors and an absence of GPIO for optional GPIO parameters. For the common
90pattern where a GPIO is optional, the gpiod_get_optional() and
91gpiod_get_index_optional() functions can be used. These functions return NULL
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +010092instead of -ENOENT if no GPIO has been assigned to the requested function::
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070093
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070094 struct gpio_desc *gpiod_get_optional(struct device *dev,
95 const char *con_id,
96 enum gpiod_flags flags)
97
98 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
99 const char *con_id,
100 unsigned int index,
101 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900102
Dmitry Torokhov22c40362017-02-12 17:13:55 -0800103Note that gpio_get*_optional() functions (and their managed variants), unlike
104the rest of gpiolib API, also return NULL when gpiolib support is disabled.
105This is helpful to driver authors, since they do not need to special case
106-ENOSYS return codes. System integrators should however be careful to enable
107gpiolib on systems that need it.
108
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100109For a function using multiple GPIOs all of those can be obtained with one call::
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100110
111 struct gpio_descs *gpiod_get_array(struct device *dev,
112 const char *con_id,
113 enum gpiod_flags flags)
114
115This function returns a struct gpio_descs which contains an array of
Janusz Krzysztofikbf9346f2018-09-05 23:50:06 +0200116descriptors. It also contains a pointer to a gpiolib private structure which,
117if passed back to get/set array functions, may speed up I/O proocessing::
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100118
119 struct gpio_descs {
Janusz Krzysztofikbf9346f2018-09-05 23:50:06 +0200120 struct gpio_array *info;
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100121 unsigned int ndescs;
122 struct gpio_desc *desc[];
123 }
124
125The following function returns NULL instead of -ENOENT if no GPIOs have been
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100126assigned to the requested function::
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100127
128 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
129 const char *con_id,
130 enum gpiod_flags flags)
131
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100132Device-managed variants of these functions are also defined::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900133
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900134 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
135 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900136
137 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
138 const char *con_id,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900139 unsigned int idx,
140 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900141
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700142 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
143 const char *con_id,
144 enum gpiod_flags flags)
145
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100146 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700147 const char *con_id,
148 unsigned int index,
149 enum gpiod_flags flags)
150
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100151 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
152 const char *con_id,
153 enum gpiod_flags flags)
154
155 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
156 const char *con_id,
157 enum gpiod_flags flags)
158
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100159A GPIO descriptor can be disposed of using the gpiod_put() function::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900160
161 void gpiod_put(struct gpio_desc *desc)
162
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100163For an array of GPIOs this function can be used::
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100164
165 void gpiod_put_array(struct gpio_descs *descs)
166
167It is strictly forbidden to use a descriptor after calling these functions.
168It is also not allowed to individually release descriptors (using gpiod_put())
169from an array acquired with gpiod_get_array().
170
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100171The device-managed variants are, unsurprisingly::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900172
173 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
174
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100175 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
176
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900177
178Using GPIOs
179===========
180
181Setting Direction
182-----------------
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900183The first thing a driver must do with a GPIO is setting its direction. If no
184direction-setting flags have been given to gpiod_get*(), this is done by
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100185invoking one of the gpiod_direction_*() functions::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900186
187 int gpiod_direction_input(struct gpio_desc *desc)
188 int gpiod_direction_output(struct gpio_desc *desc, int value)
189
190The return value is zero for success, else a negative errno. It should be
191checked, since the get/set calls don't return errors and since misconfiguration
192is possible. You should normally issue these calls from a task context. However,
193for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
194of early board setup.
195
196For output GPIOs, the value provided becomes the initial output value. This
197helps avoid signal glitching during system startup.
198
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100199A driver can also query the current direction of a GPIO::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900200
201 int gpiod_get_direction(const struct gpio_desc *desc)
202
Wolfram Sang9961dbc2018-01-09 12:35:54 +0100203This function returns 0 for output, 1 for input, or an error code in case of error.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900204
205Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
206without setting its direction first is illegal and will result in undefined
207behavior!**
208
209
210Spinlock-Safe GPIO Access
211-------------------------
212Most GPIO controllers can be accessed with memory read/write instructions. Those
213don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
214handlers and similar contexts.
215
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100216Use the following calls to access GPIOs from an atomic context::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900217
218 int gpiod_get_value(const struct gpio_desc *desc);
219 void gpiod_set_value(struct gpio_desc *desc, int value);
220
221The values are boolean, zero for low, nonzero for high. When reading the value
222of an output pin, the value returned should be what's seen on the pin. That
223won't always match the specified output value, because of issues including
224open-drain signaling and output latencies.
225
226The get/set calls do not return errors because "invalid GPIO" should have been
227reported earlier from gpiod_direction_*(). However, note that not all platforms
228can read the value of output pins; those that can't should always return zero.
229Also, using these calls for GPIOs that can't safely be accessed without sleeping
230(see below) is an error.
231
232
233GPIO Access That May Sleep
234--------------------------
235Some GPIO controllers must be accessed using message based buses like I2C or
236SPI. Commands to read or write those GPIO values require waiting to get to the
237head of a queue to transmit a command and get its response. This requires
238sleeping, which can't be done from inside IRQ handlers.
239
240Platforms that support this type of GPIO distinguish them from other GPIOs by
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100241returning nonzero from this call::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900242
243 int gpiod_cansleep(const struct gpio_desc *desc)
244
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100245To access such GPIOs, a different set of accessors is defined::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900246
247 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
248 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
249
250Accessing such GPIOs requires a context which may sleep, for example a threaded
251IRQ handler, and those accessors must be used instead of spinlock-safe
252accessors without the cansleep() name suffix.
253
254Other than the fact that these accessors might sleep, and will work on GPIOs
255that can't be accessed from hardIRQ handlers, these calls act the same as the
256spinlock-safe calls.
257
258
Hannu Hartikainenf3f10172021-07-08 18:20:54 +0300259.. _active_low_semantics:
260
Linus Walleijadbf0292018-01-18 10:43:43 +0100261The active low and open drain semantics
262---------------------------------------
263As a consumer should not have to care about the physical line level, all of the
264gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
265the *logical* value. With this they take the active low property into account.
266This means that they check whether the GPIO is configured to be active low,
267and if so, they manipulate the passed value before the physical line level is
268driven.
269
270The same is applicable for open drain or open source output lines: those do not
271actively drive their output high (open drain) or low (open source), they just
272switch their output to a high impedance value. The consumer should not need to
273care. (For details read about open drain in driver.txt.)
274
275With this, all the gpiod_set_(array)_value_xxx() functions interpret the
276parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
277level will be driven accordingly.
278
279As an example, if the active low property for a dedicated GPIO is set, and the
280gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
281will be driven low.
282
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100283To summarize::
Linus Walleijadbf0292018-01-18 10:43:43 +0100284
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100285 Function (example) line property physical line
286 gpiod_set_raw_value(desc, 0); don't care low
287 gpiod_set_raw_value(desc, 1); don't care high
288 gpiod_set_value(desc, 0); default (active high) low
289 gpiod_set_value(desc, 1); default (active high) high
290 gpiod_set_value(desc, 0); active low high
291 gpiod_set_value(desc, 1); active low low
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100292 gpiod_set_value(desc, 0); open drain low
293 gpiod_set_value(desc, 1); open drain high impedance
294 gpiod_set_value(desc, 0); open source high impedance
295 gpiod_set_value(desc, 1); open source high
Linus Walleijadbf0292018-01-18 10:43:43 +0100296
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100297It is possible to override these semantics using the set_raw/get_raw functions
Linus Walleijadbf0292018-01-18 10:43:43 +0100298but it should be avoided as much as possible, especially by system-agnostic drivers
299which should not need to care about the actual physical line level and worry about
300the logical value instead.
301
302
303Accessing raw GPIO values
304-------------------------
305Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
306their device will actually receive, no matter what lies between it and the GPIO
307line.
308
309The following set of calls ignore the active-low or open drain property of a GPIO and
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100310work on the raw line value::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900311
312 int gpiod_get_raw_value(const struct gpio_desc *desc)
313 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
314 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
315 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
Philipp Zabelef70bbe2014-01-07 12:34:11 +0100316 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900317
Hannu Hartikainenf3f10172021-07-08 18:20:54 +0300318The active low state of a GPIO can also be queried and toggled using the
319following calls::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900320
321 int gpiod_is_active_low(const struct gpio_desc *desc)
Hannu Hartikainenf3f10172021-07-08 18:20:54 +0300322 void gpiod_toggle_active_low(struct gpio_desc *desc)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900323
Linus Walleijadbf0292018-01-18 10:43:43 +0100324Note that these functions should only be used with great moderation; a driver
325should not have to care about the physical line level or open drain semantics.
Dirk Behmeac49fbd2015-07-18 08:02:07 +0200326
327
Lukas Wunnereec1d562017-10-12 12:40:10 +0200328Access multiple GPIOs with a single function call
329-------------------------------------------------
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100330The following functions get or set the values of an array of GPIOs::
Lukas Wunnereec1d562017-10-12 12:40:10 +0200331
332 int gpiod_get_array_value(unsigned int array_size,
333 struct gpio_desc **desc_array,
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200334 struct gpio_array *array_info,
Janusz Krzysztofikb9762be2018-09-05 23:50:05 +0200335 unsigned long *value_bitmap);
Lukas Wunnereec1d562017-10-12 12:40:10 +0200336 int gpiod_get_raw_array_value(unsigned int array_size,
337 struct gpio_desc **desc_array,
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200338 struct gpio_array *array_info,
Janusz Krzysztofikb9762be2018-09-05 23:50:05 +0200339 unsigned long *value_bitmap);
Lukas Wunnereec1d562017-10-12 12:40:10 +0200340 int gpiod_get_array_value_cansleep(unsigned int array_size,
341 struct gpio_desc **desc_array,
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200342 struct gpio_array *array_info,
Janusz Krzysztofikb9762be2018-09-05 23:50:05 +0200343 unsigned long *value_bitmap);
Lukas Wunnereec1d562017-10-12 12:40:10 +0200344 int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
345 struct gpio_desc **desc_array,
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200346 struct gpio_array *array_info,
Janusz Krzysztofikb9762be2018-09-05 23:50:05 +0200347 unsigned long *value_bitmap);
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100348
Geert Uytterhoevencf9af0d2018-09-27 13:38:09 +0200349 int gpiod_set_array_value(unsigned int array_size,
350 struct gpio_desc **desc_array,
351 struct gpio_array *array_info,
352 unsigned long *value_bitmap)
Geert Uytterhoevenc2937662018-09-27 13:38:08 +0200353 int gpiod_set_raw_array_value(unsigned int array_size,
354 struct gpio_desc **desc_array,
355 struct gpio_array *array_info,
356 unsigned long *value_bitmap)
Geert Uytterhoevencf9af0d2018-09-27 13:38:09 +0200357 int gpiod_set_array_value_cansleep(unsigned int array_size,
358 struct gpio_desc **desc_array,
359 struct gpio_array *array_info,
360 unsigned long *value_bitmap)
Geert Uytterhoevenc2937662018-09-27 13:38:08 +0200361 int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
362 struct gpio_desc **desc_array,
363 struct gpio_array *array_info,
364 unsigned long *value_bitmap)
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100365
Lukas Wunnereec1d562017-10-12 12:40:10 +0200366The array can be an arbitrary set of GPIOs. The functions will try to access
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100367GPIOs belonging to the same bank or chip simultaneously if supported by the
368corresponding chip driver. In that case a significantly improved performance
Lukas Wunnereec1d562017-10-12 12:40:10 +0200369can be expected. If simultaneous access is not possible the GPIOs will be
370accessed sequentially.
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100371
Jonathan Neuschäferdb63c092021-01-01 21:00:51 +0100372The functions take four arguments:
373
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100374 * array_size - the number of array elements
375 * desc_array - an array of GPIO descriptors
Geert Uytterhoeven01f14c52019-07-01 16:10:05 +0200376 * array_info - optional information obtained from gpiod_get_array()
Janusz Krzysztofikb9762be2018-09-05 23:50:05 +0200377 * value_bitmap - a bitmap to store the GPIOs' values (get) or
Jonathan Neuschäferdb63c092021-01-01 21:00:51 +0100378 a bitmap of values to assign to the GPIOs (set)
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100379
380The descriptor array can be obtained using the gpiod_get_array() function
381or one of its variants. If the group of descriptors returned by that function
Lukas Wunnereec1d562017-10-12 12:40:10 +0200382matches the desired group of GPIOs, those GPIOs can be accessed by simply using
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100383the struct gpio_descs returned by gpiod_get_array()::
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100384
385 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
Rojhalat Ibrahime2bfba42015-06-02 11:38:06 +0200386 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200387 my_gpio_descs->info, my_gpio_value_bitmap);
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100388
Lukas Wunnereec1d562017-10-12 12:40:10 +0200389It is also possible to access a completely arbitrary array of descriptors. The
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100390descriptors may be obtained using any combination of gpiod_get() and
391gpiod_get_array(). Afterwards the array of descriptors has to be setup
Janusz Krzysztofik77588c12018-09-05 23:50:07 +0200392manually before it can be passed to one of the above functions. In that case,
393array_info should be set to NULL.
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100394
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100395Note that for optimal performance GPIOs belonging to the same chip should be
396contiguous within the array of descriptors.
397
Janusz Krzysztofikb17566a2018-09-05 23:50:08 +0200398Still better performance may be achieved if array indexes of the descriptors
399match hardware pin numbers of a single chip. If an array passed to a get/set
400array function matches the one obtained from gpiod_get_array() and array_info
401associated with the array is also passed, the function may take a fast bitmap
402processing path, passing the value_bitmap argument directly to the respective
403.get/set_multiple() callback of the chip. That allows for utilization of GPIO
404banks as data I/O ports without much loss of performance.
405
Lukas Wunnereec1d562017-10-12 12:40:10 +0200406The return value of gpiod_get_array_value() and its variants is 0 on success
407or negative on error. Note the difference to gpiod_get_value(), which returns
4080 or 1 on success to convey the GPIO value. With the array functions, the GPIO
409values are stored in value_array rather than passed back as return value.
410
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100411
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900412GPIOs mapped to IRQs
413--------------------
414GPIO lines can quite often be used as IRQs. You can get the IRQ number
Jonathan Neuschäfer4e0edc42018-03-09 00:40:22 +0100415corresponding to a given GPIO using the following call::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900416
417 int gpiod_to_irq(const struct gpio_desc *desc)
418
Geert Uytterhoevencbfa2c52015-05-21 14:07:50 +0200419It will return an IRQ number, or a negative errno code if the mapping can't be
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900420done (most likely because that particular GPIO cannot be used as IRQ). It is an
421unchecked error to use a GPIO that wasn't set up as an input using
422gpiod_direction_input(), or to use an IRQ number that didn't originally come
423from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
424
425Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
426free_irq(). They will often be stored into IRQ resources for platform devices,
427by the board-specific initialization code. Note that IRQ trigger options are
428part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
429capabilities.
430
431
Rafael J. Wysockie36d4532014-11-03 23:39:57 +0100432GPIOs and ACPI
433==============
434
435On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
436the _CRS configuration objects of devices. Those resources do not provide
437connection IDs (names) for GPIOs, so it is necessary to use an additional
438mechanism for this purpose.
439
440Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
441which, among other things, may be used to provide connection IDs for specific
442GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
443case, it will be handled by the GPIO subsystem automatically. However, if the
444_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
445connection IDs need to be provided by device drivers.
446
Mauro Carvalho Chehabcb1aaeb2019-06-07 15:54:32 -0300447For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
Rafael J. Wysockie36d4532014-11-03 23:39:57 +0100448
449
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900450Interacting With the Legacy GPIO Subsystem
451==========================================
Alexandre Courbota0de6952020-11-22 18:25:48 +0900452Many kernel subsystems and drivers still handle GPIOs using the legacy
453integer-based interface. It is strongly recommended to update these to the new
454gpiod interface. For cases where both interfaces need to be used, the following
455two functions allow to convert a GPIO descriptor into the GPIO integer namespace
456and vice-versa::
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900457
458 int desc_to_gpio(const struct gpio_desc *desc)
459 struct gpio_desc *gpio_to_desc(unsigned gpio)
460
Alexandre Courbota0de6952020-11-22 18:25:48 +0900461The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
462the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
463All the same, a GPIO number passed to gpio_to_desc() must first be properly
464acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
465considered valid until that GPIO number is released using gpio_free().
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900466
467Freeing a GPIO obtained by one API with the other API is forbidden and an
468unchecked error.