1 ==================================
2 GPIO Descriptor Consumer Interface
3 ==================================
5 This document describes the consumer interface of the GPIO framework. Note that
6 it describes the new descriptor-based interface. For a description of the
7 deprecated integer-based GPIO interface please refer to legacy.rst.
10 Guidelines for GPIOs consumers
11 ==============================
13 Drivers that can't work without standard GPIO calls should have Kconfig entries
14 that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
15 obtain and use GPIOs are available by including the following file::
17 #include <linux/gpio/consumer.h>
19 There are static inline stubs for all functions in the header file in the case
20 where GPIOLIB is disabled. When these stubs are called they will emit
21 warnings. These stubs are used for two use cases:
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.
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 Combining truly optional GPIOLIB usage with calls to
33 ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird
34 error messages. Use the ordinary getter functions with optional GPIOLIB:
35 some open coding of error handling should be expected when you do this.
37 All the functions that work with the descriptor-based GPIO interface are
38 prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
39 interface. No other function in the kernel should use these prefixes. The use
40 of the legacy functions is strongly discouraged, new code should use
41 <linux/gpio/consumer.h> and descriptors exclusively.
44 Obtaining and Disposing GPIOs
45 =============================
47 With the descriptor-based interface, GPIOs are identified with an opaque,
48 non-forgeable handler that must be obtained through a call to one of the
49 gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
50 device that will use the GPIO and the function the requested GPIO is supposed to
53 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
54 enum gpiod_flags flags)
56 If a function is implemented by using several GPIOs together (e.g. a simple LED
57 device that displays digits), an additional index argument can be specified::
59 struct gpio_desc *gpiod_get_index(struct device *dev,
60 const char *con_id, unsigned int idx,
61 enum gpiod_flags flags)
63 For a more detailed description of the con_id parameter in the DeviceTree case
64 see Documentation/driver-api/gpio/board.rst
66 The flags parameter is used to optionally specify a direction and initial value
67 for the GPIO. Values can be:
69 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
70 later with one of the dedicated functions.
71 * GPIOD_IN to initialize the GPIO as input.
72 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
73 * GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
74 * GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
75 to be electrically used with open drain.
76 * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
77 to be electrically used with open drain.
79 Note that the initial value is *logical* and the physical line level depends on
80 whether the line is configured active high or active low (see
81 :ref:`active_low_semantics`).
83 The two last flags are used for use cases where open drain is mandatory, such
84 as I2C: if the line is not already configured as open drain in the mappings
85 (see board.rst), then open drain will be enforced anyway and a warning will be
86 printed that the board configuration needs to be updated to match the use case.
88 Both functions return either a valid GPIO descriptor, or an error code checkable
89 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
90 if and only if no GPIO has been assigned to the device/function/index triplet,
91 other error codes are used for cases where a GPIO has been assigned but an error
92 occurred while trying to acquire it. This is useful to discriminate between mere
93 errors and an absence of GPIO for optional GPIO parameters. For the common
94 pattern where a GPIO is optional, the gpiod_get_optional() and
95 gpiod_get_index_optional() functions can be used. These functions return NULL
96 instead of -ENOENT if no GPIO has been assigned to the requested function::
98 struct gpio_desc *gpiod_get_optional(struct device *dev,
100 enum gpiod_flags flags)
102 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
105 enum gpiod_flags flags)
107 Note that gpio_get*_optional() functions (and their managed variants), unlike
108 the rest of gpiolib API, also return NULL when gpiolib support is disabled.
109 This is helpful to driver authors, since they do not need to special case
110 -ENOSYS return codes. System integrators should however be careful to enable
111 gpiolib on systems that need it.
113 For a function using multiple GPIOs all of those can be obtained with one call::
115 struct gpio_descs *gpiod_get_array(struct device *dev,
117 enum gpiod_flags flags)
119 This function returns a struct gpio_descs which contains an array of
120 descriptors. It also contains a pointer to a gpiolib private structure which,
121 if passed back to get/set array functions, may speed up I/O processing::
124 struct gpio_array *info;
126 struct gpio_desc *desc[];
129 The following function returns NULL instead of -ENOENT if no GPIOs have been
130 assigned to the requested function::
132 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
134 enum gpiod_flags flags)
136 Device-managed variants of these functions are also defined::
138 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
139 enum gpiod_flags flags)
141 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
144 enum gpiod_flags flags)
146 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
148 enum gpiod_flags flags)
150 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
153 enum gpiod_flags flags)
155 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
157 enum gpiod_flags flags)
159 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
161 enum gpiod_flags flags)
163 A GPIO descriptor can be disposed of using the gpiod_put() function::
165 void gpiod_put(struct gpio_desc *desc)
167 For an array of GPIOs this function can be used::
169 void gpiod_put_array(struct gpio_descs *descs)
171 It is strictly forbidden to use a descriptor after calling these functions.
172 It is also not allowed to individually release descriptors (using gpiod_put())
173 from an array acquired with gpiod_get_array().
175 The device-managed variants are, unsurprisingly::
177 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
179 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
187 The first thing a driver must do with a GPIO is setting its direction. If no
188 direction-setting flags have been given to gpiod_get*(), this is done by
189 invoking one of the gpiod_direction_*() functions::
191 int gpiod_direction_input(struct gpio_desc *desc)
192 int gpiod_direction_output(struct gpio_desc *desc, int value)
194 The return value is zero for success, else a negative errno. It should be
195 checked, since the get/set calls don't return errors and since misconfiguration
196 is possible. You should normally issue these calls from a task context. However,
197 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
198 of early board setup.
200 For output GPIOs, the value provided becomes the initial output value. This
201 helps avoid signal glitching during system startup.
203 A driver can also query the current direction of a GPIO::
205 int gpiod_get_direction(const struct gpio_desc *desc)
207 This function returns 0 for output, 1 for input, or an error code in case of error.
209 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
210 without setting its direction first is illegal and will result in undefined
214 Spinlock-Safe GPIO Access
215 -------------------------
216 Most GPIO controllers can be accessed with memory read/write instructions. Those
217 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
218 handlers and similar contexts.
220 Use the following calls to access GPIOs from an atomic context::
222 int gpiod_get_value(const struct gpio_desc *desc);
223 void gpiod_set_value(struct gpio_desc *desc, int value);
225 The values are boolean, zero for low, nonzero for high. When reading the value
226 of an output pin, the value returned should be what's seen on the pin. That
227 won't always match the specified output value, because of issues including
228 open-drain signaling and output latencies.
230 The get/set calls do not return errors because "invalid GPIO" should have been
231 reported earlier from gpiod_direction_*(). However, note that not all platforms
232 can read the value of output pins; those that can't should always return zero.
233 Also, using these calls for GPIOs that can't safely be accessed without sleeping
234 (see below) is an error.
237 GPIO Access That May Sleep
238 --------------------------
239 Some GPIO controllers must be accessed using message based buses like I2C or
240 SPI. Commands to read or write those GPIO values require waiting to get to the
241 head of a queue to transmit a command and get its response. This requires
242 sleeping, which can't be done from inside IRQ handlers.
244 Platforms that support this type of GPIO distinguish them from other GPIOs by
245 returning nonzero from this call::
247 int gpiod_cansleep(const struct gpio_desc *desc)
249 To access such GPIOs, a different set of accessors is defined::
251 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
252 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
254 Accessing such GPIOs requires a context which may sleep, for example a threaded
255 IRQ handler, and those accessors must be used instead of spinlock-safe
256 accessors without the cansleep() name suffix.
258 Other than the fact that these accessors might sleep, and will work on GPIOs
259 that can't be accessed from hardIRQ handlers, these calls act the same as the
263 .. _active_low_semantics:
265 The active low and open drain semantics
266 ---------------------------------------
267 As a consumer should not have to care about the physical line level, all of the
268 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
269 the *logical* value. With this they take the active low property into account.
270 This means that they check whether the GPIO is configured to be active low,
271 and if so, they manipulate the passed value before the physical line level is
274 The same is applicable for open drain or open source output lines: those do not
275 actively drive their output high (open drain) or low (open source), they just
276 switch their output to a high impedance value. The consumer should not need to
277 care. (For details read about open drain in driver.rst.)
279 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
280 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
281 level will be driven accordingly.
283 As an example, if the active low property for a dedicated GPIO is set, and the
284 gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
289 Function (example) line property physical line
290 gpiod_set_raw_value(desc, 0); don't care low
291 gpiod_set_raw_value(desc, 1); don't care high
292 gpiod_set_value(desc, 0); default (active high) low
293 gpiod_set_value(desc, 1); default (active high) high
294 gpiod_set_value(desc, 0); active low high
295 gpiod_set_value(desc, 1); active low low
296 gpiod_set_value(desc, 0); open drain low
297 gpiod_set_value(desc, 1); open drain high impedance
298 gpiod_set_value(desc, 0); open source high impedance
299 gpiod_set_value(desc, 1); open source high
301 It is possible to override these semantics using the set_raw/get_raw functions
302 but it should be avoided as much as possible, especially by system-agnostic drivers
303 which should not need to care about the actual physical line level and worry about
304 the logical value instead.
307 Accessing raw GPIO values
308 -------------------------
309 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
310 their device will actually receive, no matter what lies between it and the GPIO
313 The following set of calls ignore the active-low or open drain property of a GPIO and
314 work on the raw line value::
316 int gpiod_get_raw_value(const struct gpio_desc *desc)
317 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
318 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
319 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
320 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
322 The active low state of a GPIO can also be queried and toggled using the
325 int gpiod_is_active_low(const struct gpio_desc *desc)
326 void gpiod_toggle_active_low(struct gpio_desc *desc)
328 Note that these functions should only be used with great moderation; a driver
329 should not have to care about the physical line level or open drain semantics.
332 Access multiple GPIOs with a single function call
333 -------------------------------------------------
334 The following functions get or set the values of an array of GPIOs::
336 int gpiod_get_array_value(unsigned int array_size,
337 struct gpio_desc **desc_array,
338 struct gpio_array *array_info,
339 unsigned long *value_bitmap);
340 int gpiod_get_raw_array_value(unsigned int array_size,
341 struct gpio_desc **desc_array,
342 struct gpio_array *array_info,
343 unsigned long *value_bitmap);
344 int gpiod_get_array_value_cansleep(unsigned int array_size,
345 struct gpio_desc **desc_array,
346 struct gpio_array *array_info,
347 unsigned long *value_bitmap);
348 int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
349 struct gpio_desc **desc_array,
350 struct gpio_array *array_info,
351 unsigned long *value_bitmap);
353 int gpiod_set_array_value(unsigned int array_size,
354 struct gpio_desc **desc_array,
355 struct gpio_array *array_info,
356 unsigned long *value_bitmap)
357 int gpiod_set_raw_array_value(unsigned int array_size,
358 struct gpio_desc **desc_array,
359 struct gpio_array *array_info,
360 unsigned long *value_bitmap)
361 int gpiod_set_array_value_cansleep(unsigned int array_size,
362 struct gpio_desc **desc_array,
363 struct gpio_array *array_info,
364 unsigned long *value_bitmap)
365 int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
366 struct gpio_desc **desc_array,
367 struct gpio_array *array_info,
368 unsigned long *value_bitmap)
370 The array can be an arbitrary set of GPIOs. The functions will try to access
371 GPIOs belonging to the same bank or chip simultaneously if supported by the
372 corresponding chip driver. In that case a significantly improved performance
373 can be expected. If simultaneous access is not possible the GPIOs will be
374 accessed sequentially.
376 The functions take four arguments:
378 * array_size - the number of array elements
379 * desc_array - an array of GPIO descriptors
380 * array_info - optional information obtained from gpiod_get_array()
381 * value_bitmap - a bitmap to store the GPIOs' values (get) or
382 a bitmap of values to assign to the GPIOs (set)
384 The descriptor array can be obtained using the gpiod_get_array() function
385 or one of its variants. If the group of descriptors returned by that function
386 matches the desired group of GPIOs, those GPIOs can be accessed by simply using
387 the struct gpio_descs returned by gpiod_get_array()::
389 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
390 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
391 my_gpio_descs->info, my_gpio_value_bitmap);
393 It is also possible to access a completely arbitrary array of descriptors. The
394 descriptors may be obtained using any combination of gpiod_get() and
395 gpiod_get_array(). Afterwards the array of descriptors has to be setup
396 manually before it can be passed to one of the above functions. In that case,
397 array_info should be set to NULL.
399 Note that for optimal performance GPIOs belonging to the same chip should be
400 contiguous within the array of descriptors.
402 Still better performance may be achieved if array indexes of the descriptors
403 match hardware pin numbers of a single chip. If an array passed to a get/set
404 array function matches the one obtained from gpiod_get_array() and array_info
405 associated with the array is also passed, the function may take a fast bitmap
406 processing path, passing the value_bitmap argument directly to the respective
407 .get/set_multiple() callback of the chip. That allows for utilization of GPIO
408 banks as data I/O ports without much loss of performance.
410 The return value of gpiod_get_array_value() and its variants is 0 on success
411 or negative on error. Note the difference to gpiod_get_value(), which returns
412 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
413 values are stored in value_array rather than passed back as return value.
418 GPIO lines can quite often be used as IRQs. You can get the IRQ number
419 corresponding to a given GPIO using the following call::
421 int gpiod_to_irq(const struct gpio_desc *desc)
423 It will return an IRQ number, or a negative errno code if the mapping can't be
424 done (most likely because that particular GPIO cannot be used as IRQ). It is an
425 unchecked error to use a GPIO that wasn't set up as an input using
426 gpiod_direction_input(), or to use an IRQ number that didn't originally come
427 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
429 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
430 free_irq(). They will often be stored into IRQ resources for platform devices,
431 by the board-specific initialization code. Note that IRQ trigger options are
432 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
439 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
440 the _CRS configuration objects of devices. Those resources do not provide
441 connection IDs (names) for GPIOs, so it is necessary to use an additional
442 mechanism for this purpose.
444 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
445 which, among other things, may be used to provide connection IDs for specific
446 GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
447 case, it will be handled by the GPIO subsystem automatically. However, if the
448 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
449 connection IDs need to be provided by device drivers.
451 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
454 Interacting With the Legacy GPIO Subsystem
455 ==========================================
456 Many kernel subsystems and drivers still handle GPIOs using the legacy
457 integer-based interface. It is strongly recommended to update these to the new
458 gpiod interface. For cases where both interfaces need to be used, the following
459 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
462 int desc_to_gpio(const struct gpio_desc *desc)
463 struct gpio_desc *gpio_to_desc(unsigned gpio)
465 The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
466 the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
467 All the same, a GPIO number passed to gpio_to_desc() must first be properly
468 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
469 considered valid until that GPIO number is released using gpio_free().
471 Freeing a GPIO obtained by one API with the other API is forbidden and an