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Alexandre Courbotfd8e1982013-11-16 21:34:21 +09001GPIO Descriptor Consumer Interface
2==================================
3
4This document describes the consumer interface of the GPIO framework. Note that
5it describes the new descriptor-based interface. For a description of the
6deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
7
8
9Guidelines for GPIOs consumers
10==============================
11
12Drivers that can't work without standard GPIO calls should have Kconfig entries
13that depend on GPIOLIB. The functions that allow a driver to obtain and use
14GPIOs are available by including the following file:
15
16 #include <linux/gpio/consumer.h>
17
18All the functions that work with the descriptor-based GPIO interface are
19prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
20other function in the kernel should use these prefixes.
21
22
23Obtaining and Disposing GPIOs
24=============================
25
26With the descriptor-based interface, GPIOs are identified with an opaque,
27non-forgeable handler that must be obtained through a call to one of the
28gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
29device that will use the GPIO and the function the requested GPIO is supposed to
30fulfill:
31
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090032 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
33 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090034
35If a function is implemented by using several GPIOs together (e.g. a simple LED
36device that displays digits), an additional index argument can be specified:
37
38 struct gpio_desc *gpiod_get_index(struct device *dev,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090039 const char *con_id, unsigned int idx,
40 enum gpiod_flags flags)
41
Dirk Behme87e77e42015-09-02 20:07:10 +020042For a more detailed description of the con_id parameter in the DeviceTree case
43see Documentation/gpio/board.txt
44
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090045The flags parameter is used to optionally specify a direction and initial value
46for the GPIO. Values can be:
47
48* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
49 later with one of the dedicated functions.
50* GPIOD_IN to initialize the GPIO as input.
51* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
52* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090053
54Both functions return either a valid GPIO descriptor, or an error code checkable
Alexandre Courbot2a3cf6a2013-12-11 11:32:28 +090055with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
56if and only if no GPIO has been assigned to the device/function/index triplet,
57other error codes are used for cases where a GPIO has been assigned but an error
Carlos Garciac98be0c2014-04-04 22:31:00 -040058occurred while trying to acquire it. This is useful to discriminate between mere
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070059errors and an absence of GPIO for optional GPIO parameters. For the common
60pattern where a GPIO is optional, the gpiod_get_optional() and
61gpiod_get_index_optional() functions can be used. These functions return NULL
62instead of -ENOENT if no GPIO has been assigned to the requested function:
63
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070064 struct gpio_desc *gpiod_get_optional(struct device *dev,
65 const char *con_id,
66 enum gpiod_flags flags)
67
68 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
69 const char *con_id,
70 unsigned int index,
71 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090072
Dmitry Torokhov22c40362017-02-12 17:13:55 -080073Note that gpio_get*_optional() functions (and their managed variants), unlike
74the rest of gpiolib API, also return NULL when gpiolib support is disabled.
75This is helpful to driver authors, since they do not need to special case
76-ENOSYS return codes. System integrators should however be careful to enable
77gpiolib on systems that need it.
78
Rojhalat Ibrahim66858522015-02-11 17:27:58 +010079For a function using multiple GPIOs all of those can be obtained with one call:
80
81 struct gpio_descs *gpiod_get_array(struct device *dev,
82 const char *con_id,
83 enum gpiod_flags flags)
84
85This function returns a struct gpio_descs which contains an array of
86descriptors:
87
88 struct gpio_descs {
89 unsigned int ndescs;
90 struct gpio_desc *desc[];
91 }
92
93The following function returns NULL instead of -ENOENT if no GPIOs have been
94assigned to the requested function:
95
96 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
97 const char *con_id,
98 enum gpiod_flags flags)
99
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900100Device-managed variants of these functions are also defined:
101
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900102 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
103 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900104
105 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
106 const char *con_id,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900107 unsigned int idx,
108 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900109
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700110 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
111 const char *con_id,
112 enum gpiod_flags flags)
113
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100114 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700115 const char *con_id,
116 unsigned int index,
117 enum gpiod_flags flags)
118
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100119 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
120 const char *con_id,
121 enum gpiod_flags flags)
122
123 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
124 const char *con_id,
125 enum gpiod_flags flags)
126
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900127A GPIO descriptor can be disposed of using the gpiod_put() function:
128
129 void gpiod_put(struct gpio_desc *desc)
130
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100131For an array of GPIOs this function can be used:
132
133 void gpiod_put_array(struct gpio_descs *descs)
134
135It is strictly forbidden to use a descriptor after calling these functions.
136It is also not allowed to individually release descriptors (using gpiod_put())
137from an array acquired with gpiod_get_array().
138
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100139The device-managed variants are, unsurprisingly:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900140
141 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
142
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100143 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
144
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900145
146Using GPIOs
147===========
148
149Setting Direction
150-----------------
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900151The first thing a driver must do with a GPIO is setting its direction. If no
152direction-setting flags have been given to gpiod_get*(), this is done by
153invoking one of the gpiod_direction_*() functions:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900154
155 int gpiod_direction_input(struct gpio_desc *desc)
156 int gpiod_direction_output(struct gpio_desc *desc, int value)
157
158The return value is zero for success, else a negative errno. It should be
159checked, since the get/set calls don't return errors and since misconfiguration
160is possible. You should normally issue these calls from a task context. However,
161for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
162of early board setup.
163
164For output GPIOs, the value provided becomes the initial output value. This
165helps avoid signal glitching during system startup.
166
167A driver can also query the current direction of a GPIO:
168
169 int gpiod_get_direction(const struct gpio_desc *desc)
170
171This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.
172
173Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
174without setting its direction first is illegal and will result in undefined
175behavior!**
176
177
178Spinlock-Safe GPIO Access
179-------------------------
180Most GPIO controllers can be accessed with memory read/write instructions. Those
181don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
182handlers and similar contexts.
183
184Use the following calls to access GPIOs from an atomic context:
185
186 int gpiod_get_value(const struct gpio_desc *desc);
187 void gpiod_set_value(struct gpio_desc *desc, int value);
188
189The values are boolean, zero for low, nonzero for high. When reading the value
190of an output pin, the value returned should be what's seen on the pin. That
191won't always match the specified output value, because of issues including
192open-drain signaling and output latencies.
193
194The get/set calls do not return errors because "invalid GPIO" should have been
195reported earlier from gpiod_direction_*(). However, note that not all platforms
196can read the value of output pins; those that can't should always return zero.
197Also, using these calls for GPIOs that can't safely be accessed without sleeping
198(see below) is an error.
199
200
201GPIO Access That May Sleep
202--------------------------
203Some GPIO controllers must be accessed using message based buses like I2C or
204SPI. Commands to read or write those GPIO values require waiting to get to the
205head of a queue to transmit a command and get its response. This requires
206sleeping, which can't be done from inside IRQ handlers.
207
208Platforms that support this type of GPIO distinguish them from other GPIOs by
209returning nonzero from this call:
210
211 int gpiod_cansleep(const struct gpio_desc *desc)
212
213To access such GPIOs, a different set of accessors is defined:
214
215 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
216 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
217
218Accessing such GPIOs requires a context which may sleep, for example a threaded
219IRQ handler, and those accessors must be used instead of spinlock-safe
220accessors without the cansleep() name suffix.
221
222Other than the fact that these accessors might sleep, and will work on GPIOs
223that can't be accessed from hardIRQ handlers, these calls act the same as the
224spinlock-safe calls.
225
226
227Active-low State and Raw GPIO Values
228------------------------------------
229Device drivers like to manage the logical state of a GPIO, i.e. the value their
230device will actually receive, no matter what lies between it and the GPIO line.
231In some cases, it might make sense to control the actual GPIO line value. The
232following set of calls ignore the active-low property of a GPIO and work on the
233raw line value:
234
235 int gpiod_get_raw_value(const struct gpio_desc *desc)
236 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
237 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
238 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
Philipp Zabelef70bbe2014-01-07 12:34:11 +0100239 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900240
241The active-low state of a GPIO can also be queried using the following call:
242
243 int gpiod_is_active_low(const struct gpio_desc *desc)
244
245Note that these functions should only be used with great moderation ; a driver
246should not have to care about the physical line level.
247
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100248
Dirk Behmeac49fbd2015-07-18 08:02:07 +0200249The active-low property
250-----------------------
251
252As a driver should not have to care about the physical line level, all of the
253gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
254the *logical* value. With this they take the active-low property into account.
255This means that they check whether the GPIO is configured to be active-low,
256and if so, they manipulate the passed value before the physical line level is
257driven.
258
259With this, all the gpiod_set_(array)_value_xxx() functions interpret the
260parameter "value" as "active" ("1") or "inactive" ("0"). The physical line
261level will be driven accordingly.
262
263As an example, if the active-low property for a dedicated GPIO is set, and the
264gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
265will be driven low.
266
267To summarize:
268
Masanari Iida547d4c12015-11-16 20:00:35 +0900269Function (example) active-low property physical line
Dirk Behmeac49fbd2015-07-18 08:02:07 +0200270gpiod_set_raw_value(desc, 0); don't care low
271gpiod_set_raw_value(desc, 1); don't care high
272gpiod_set_value(desc, 0); default (active-high) low
273gpiod_set_value(desc, 1); default (active-high) high
274gpiod_set_value(desc, 0); active-low high
275gpiod_set_value(desc, 1); active-low low
276
277Please note again that the set_raw/get_raw functions should be avoided as much
278as possible, especially by drivers which should not care about the actual
279physical line level and worry about the logical value instead.
280
281
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100282Set multiple GPIO outputs with a single function call
283-----------------------------------------------------
284The following functions set the output values of an array of GPIOs:
285
Rojhalat Ibrahime2bfba42015-06-02 11:38:06 +0200286 void gpiod_set_array_value(unsigned int array_size,
287 struct gpio_desc **desc_array,
288 int *value_array)
289 void gpiod_set_raw_array_value(unsigned int array_size,
290 struct gpio_desc **desc_array,
291 int *value_array)
292 void gpiod_set_array_value_cansleep(unsigned int array_size,
293 struct gpio_desc **desc_array,
294 int *value_array)
295 void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
296 struct gpio_desc **desc_array,
297 int *value_array)
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100298
299The array can be an arbitrary set of GPIOs. The functions will try to set
300GPIOs belonging to the same bank or chip simultaneously if supported by the
301corresponding chip driver. In that case a significantly improved performance
302can be expected. If simultaneous setting is not possible the GPIOs will be set
303sequentially.
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100304
305The gpiod_set_array() functions take three arguments:
306 * array_size - the number of array elements
307 * desc_array - an array of GPIO descriptors
308 * value_array - an array of values to assign to the GPIOs
309
310The descriptor array can be obtained using the gpiod_get_array() function
311or one of its variants. If the group of descriptors returned by that function
312matches the desired group of GPIOs, those GPIOs can be set by simply using
313the struct gpio_descs returned by gpiod_get_array():
314
315 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
Rojhalat Ibrahime2bfba42015-06-02 11:38:06 +0200316 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
317 my_gpio_values);
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100318
319It is also possible to set a completely arbitrary array of descriptors. The
320descriptors may be obtained using any combination of gpiod_get() and
321gpiod_get_array(). Afterwards the array of descriptors has to be setup
322manually before it can be used with gpiod_set_array().
323
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100324Note that for optimal performance GPIOs belonging to the same chip should be
325contiguous within the array of descriptors.
326
327
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900328GPIOs mapped to IRQs
329--------------------
330GPIO lines can quite often be used as IRQs. You can get the IRQ number
331corresponding to a given GPIO using the following call:
332
333 int gpiod_to_irq(const struct gpio_desc *desc)
334
Geert Uytterhoevencbfa2c52015-05-21 14:07:50 +0200335It will return an IRQ number, or a negative errno code if the mapping can't be
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900336done (most likely because that particular GPIO cannot be used as IRQ). It is an
337unchecked error to use a GPIO that wasn't set up as an input using
338gpiod_direction_input(), or to use an IRQ number that didn't originally come
339from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
340
341Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
342free_irq(). They will often be stored into IRQ resources for platform devices,
343by the board-specific initialization code. Note that IRQ trigger options are
344part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
345capabilities.
346
347
Rafael J. Wysockie36d4532014-11-03 23:39:57 +0100348GPIOs and ACPI
349==============
350
351On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
352the _CRS configuration objects of devices. Those resources do not provide
353connection IDs (names) for GPIOs, so it is necessary to use an additional
354mechanism for this purpose.
355
356Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
357which, among other things, may be used to provide connection IDs for specific
358GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
359case, it will be handled by the GPIO subsystem automatically. However, if the
360_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
361connection IDs need to be provided by device drivers.
362
363For details refer to Documentation/acpi/gpio-properties.txt
364
365
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900366Interacting With the Legacy GPIO Subsystem
367==========================================
368Many kernel subsystems still handle GPIOs using the legacy integer-based
369interface. Although it is strongly encouraged to upgrade them to the safer
370descriptor-based API, the following two functions allow you to convert a GPIO
371descriptor into the GPIO integer namespace and vice-versa:
372
373 int desc_to_gpio(const struct gpio_desc *desc)
374 struct gpio_desc *gpio_to_desc(unsigned gpio)
375
376The GPIO number returned by desc_to_gpio() can be safely used as long as the
377GPIO descriptor has not been freed. All the same, a GPIO number passed to
378gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
379descriptor is only possible after the GPIO number has been released.
380
381Freeing a GPIO obtained by one API with the other API is forbidden and an
382unchecked error.