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 gpio-legacy.txt.
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.
33 All the functions that work with the descriptor-based GPIO interface are
34 prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
35 interface. No other function in the kernel should use these prefixes. The use
36 of the legacy functions is strongly discouraged, new code should use
37 <linux/gpio/consumer.h> and descriptors exclusively.
40 Obtaining and Disposing GPIOs
41 =============================
43 With the descriptor-based interface, GPIOs are identified with an opaque,
44 non-forgeable handler that must be obtained through a call to one of the
45 gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
46 device that will use the GPIO and the function the requested GPIO is supposed to
49 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
50 enum gpiod_flags flags)
52 If a function is implemented by using several GPIOs together (e.g. a simple LED
53 device that displays digits), an additional index argument can be specified::
55 struct gpio_desc *gpiod_get_index(struct device *dev,
56 const char *con_id, unsigned int idx,
57 enum gpiod_flags flags)
59 For a more detailed description of the con_id parameter in the DeviceTree case
60 see Documentation/driver-api/gpio/board.rst
62 The flags parameter is used to optionally specify a direction and initial value
63 for the GPIO. Values can be:
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.
70 * 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.
75 Note that the initial value is *logical* and the physical line level depends on
76 whether the line is configured active high or active low (see
77 :ref:`active_low_semantics`).
79 The two last flags are used for use cases where open drain is mandatory, such
80 as 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
82 printed that the board configuration needs to be updated to match the use case.
84 Both functions return either a valid GPIO descriptor, or an error code checkable
85 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
86 if and only if no GPIO has been assigned to the device/function/index triplet,
87 other error codes are used for cases where a GPIO has been assigned but an error
88 occurred while trying to acquire it. This is useful to discriminate between mere
89 errors and an absence of GPIO for optional GPIO parameters. For the common
90 pattern where a GPIO is optional, the gpiod_get_optional() and
91 gpiod_get_index_optional() functions can be used. These functions return NULL
92 instead of -ENOENT if no GPIO has been assigned to the requested function::
94 struct gpio_desc *gpiod_get_optional(struct device *dev,
96 enum gpiod_flags flags)
98 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
101 enum gpiod_flags flags)
103 Note that gpio_get*_optional() functions (and their managed variants), unlike
104 the rest of gpiolib API, also return NULL when gpiolib support is disabled.
105 This 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
107 gpiolib on systems that need it.
109 For a function using multiple GPIOs all of those can be obtained with one call::
111 struct gpio_descs *gpiod_get_array(struct device *dev,
113 enum gpiod_flags flags)
115 This function returns a struct gpio_descs which contains an array of
116 descriptors. It also contains a pointer to a gpiolib private structure which,
117 if passed back to get/set array functions, may speed up I/O proocessing::
120 struct gpio_array *info;
122 struct gpio_desc *desc[];
125 The following function returns NULL instead of -ENOENT if no GPIOs have been
126 assigned to the requested function::
128 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
130 enum gpiod_flags flags)
132 Device-managed variants of these functions are also defined::
134 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
135 enum gpiod_flags flags)
137 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
140 enum gpiod_flags flags)
142 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
144 enum gpiod_flags flags)
146 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
149 enum gpiod_flags flags)
151 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
153 enum gpiod_flags flags)
155 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
157 enum gpiod_flags flags)
159 A GPIO descriptor can be disposed of using the gpiod_put() function::
161 void gpiod_put(struct gpio_desc *desc)
163 For an array of GPIOs this function can be used::
165 void gpiod_put_array(struct gpio_descs *descs)
167 It is strictly forbidden to use a descriptor after calling these functions.
168 It is also not allowed to individually release descriptors (using gpiod_put())
169 from an array acquired with gpiod_get_array().
171 The device-managed variants are, unsurprisingly::
173 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
175 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
183 The first thing a driver must do with a GPIO is setting its direction. If no
184 direction-setting flags have been given to gpiod_get*(), this is done by
185 invoking one of the gpiod_direction_*() functions::
187 int gpiod_direction_input(struct gpio_desc *desc)
188 int gpiod_direction_output(struct gpio_desc *desc, int value)
190 The return value is zero for success, else a negative errno. It should be
191 checked, since the get/set calls don't return errors and since misconfiguration
192 is possible. You should normally issue these calls from a task context. However,
193 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
194 of early board setup.
196 For output GPIOs, the value provided becomes the initial output value. This
197 helps avoid signal glitching during system startup.
199 A driver can also query the current direction of a GPIO::
201 int gpiod_get_direction(const struct gpio_desc *desc)
203 This function returns 0 for output, 1 for input, or an error code in case of error.
205 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
206 without setting its direction first is illegal and will result in undefined
210 Spinlock-Safe GPIO Access
211 -------------------------
212 Most GPIO controllers can be accessed with memory read/write instructions. Those
213 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
214 handlers and similar contexts.
216 Use the following calls to access GPIOs from an atomic context::
218 int gpiod_get_value(const struct gpio_desc *desc);
219 void gpiod_set_value(struct gpio_desc *desc, int value);
221 The values are boolean, zero for low, nonzero for high. When reading the value
222 of an output pin, the value returned should be what's seen on the pin. That
223 won't always match the specified output value, because of issues including
224 open-drain signaling and output latencies.
226 The get/set calls do not return errors because "invalid GPIO" should have been
227 reported earlier from gpiod_direction_*(). However, note that not all platforms
228 can read the value of output pins; those that can't should always return zero.
229 Also, using these calls for GPIOs that can't safely be accessed without sleeping
230 (see below) is an error.
233 GPIO Access That May Sleep
234 --------------------------
235 Some GPIO controllers must be accessed using message based buses like I2C or
236 SPI. Commands to read or write those GPIO values require waiting to get to the
237 head of a queue to transmit a command and get its response. This requires
238 sleeping, which can't be done from inside IRQ handlers.
240 Platforms that support this type of GPIO distinguish them from other GPIOs by
241 returning nonzero from this call::
243 int gpiod_cansleep(const struct gpio_desc *desc)
245 To access such GPIOs, a different set of accessors is defined::
247 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
248 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
250 Accessing such GPIOs requires a context which may sleep, for example a threaded
251 IRQ handler, and those accessors must be used instead of spinlock-safe
252 accessors without the cansleep() name suffix.
254 Other than the fact that these accessors might sleep, and will work on GPIOs
255 that can't be accessed from hardIRQ handlers, these calls act the same as the
259 .. _active_low_semantics:
261 The active low and open drain semantics
262 ---------------------------------------
263 As a consumer should not have to care about the physical line level, all of the
264 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
265 the *logical* value. With this they take the active low property into account.
266 This means that they check whether the GPIO is configured to be active low,
267 and if so, they manipulate the passed value before the physical line level is
270 The same is applicable for open drain or open source output lines: those do not
271 actively drive their output high (open drain) or low (open source), they just
272 switch their output to a high impedance value. The consumer should not need to
273 care. (For details read about open drain in driver.txt.)
275 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
276 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
277 level will be driven accordingly.
279 As an example, if the active low property for a dedicated GPIO is set, and the
280 gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
285 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
292 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
297 It is possible to override these semantics using the set_raw/get_raw functions
298 but it should be avoided as much as possible, especially by system-agnostic drivers
299 which should not need to care about the actual physical line level and worry about
300 the logical value instead.
303 Accessing raw GPIO values
304 -------------------------
305 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
306 their device will actually receive, no matter what lies between it and the GPIO
309 The following set of calls ignore the active-low or open drain property of a GPIO and
310 work on the raw line value::
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)
316 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
318 The active low state of a GPIO can also be queried and toggled using the
321 int gpiod_is_active_low(const struct gpio_desc *desc)
322 void gpiod_toggle_active_low(struct gpio_desc *desc)
324 Note that these functions should only be used with great moderation; a driver
325 should not have to care about the physical line level or open drain semantics.
328 Access multiple GPIOs with a single function call
329 -------------------------------------------------
330 The following functions get or set the values of an array of GPIOs::
332 int gpiod_get_array_value(unsigned int array_size,
333 struct gpio_desc **desc_array,
334 struct gpio_array *array_info,
335 unsigned long *value_bitmap);
336 int gpiod_get_raw_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_array_value_cansleep(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_raw_array_value_cansleep(unsigned int array_size,
345 struct gpio_desc **desc_array,
346 struct gpio_array *array_info,
347 unsigned long *value_bitmap);
349 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)
353 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)
357 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)
361 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)
366 The array can be an arbitrary set of GPIOs. The functions will try to access
367 GPIOs belonging to the same bank or chip simultaneously if supported by the
368 corresponding chip driver. In that case a significantly improved performance
369 can be expected. If simultaneous access is not possible the GPIOs will be
370 accessed sequentially.
372 The functions take four arguments:
374 * array_size - the number of array elements
375 * desc_array - an array of GPIO descriptors
376 * array_info - optional information obtained from gpiod_get_array()
377 * value_bitmap - a bitmap to store the GPIOs' values (get) or
378 a bitmap of values to assign to the GPIOs (set)
380 The descriptor array can be obtained using the gpiod_get_array() function
381 or one of its variants. If the group of descriptors returned by that function
382 matches the desired group of GPIOs, those GPIOs can be accessed by simply using
383 the struct gpio_descs returned by gpiod_get_array()::
385 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
386 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
387 my_gpio_descs->info, my_gpio_value_bitmap);
389 It is also possible to access a completely arbitrary array of descriptors. The
390 descriptors may be obtained using any combination of gpiod_get() and
391 gpiod_get_array(). Afterwards the array of descriptors has to be setup
392 manually before it can be passed to one of the above functions. In that case,
393 array_info should be set to NULL.
395 Note that for optimal performance GPIOs belonging to the same chip should be
396 contiguous within the array of descriptors.
398 Still better performance may be achieved if array indexes of the descriptors
399 match hardware pin numbers of a single chip. If an array passed to a get/set
400 array function matches the one obtained from gpiod_get_array() and array_info
401 associated with the array is also passed, the function may take a fast bitmap
402 processing path, passing the value_bitmap argument directly to the respective
403 .get/set_multiple() callback of the chip. That allows for utilization of GPIO
404 banks as data I/O ports without much loss of performance.
406 The return value of gpiod_get_array_value() and its variants is 0 on success
407 or negative on error. Note the difference to gpiod_get_value(), which returns
408 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
409 values are stored in value_array rather than passed back as return value.
414 GPIO lines can quite often be used as IRQs. You can get the IRQ number
415 corresponding to a given GPIO using the following call::
417 int gpiod_to_irq(const struct gpio_desc *desc)
419 It will return an IRQ number, or a negative errno code if the mapping can't be
420 done (most likely because that particular GPIO cannot be used as IRQ). It is an
421 unchecked error to use a GPIO that wasn't set up as an input using
422 gpiod_direction_input(), or to use an IRQ number that didn't originally come
423 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
425 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
426 free_irq(). They will often be stored into IRQ resources for platform devices,
427 by the board-specific initialization code. Note that IRQ trigger options are
428 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
435 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
436 the _CRS configuration objects of devices. Those resources do not provide
437 connection IDs (names) for GPIOs, so it is necessary to use an additional
438 mechanism for this purpose.
440 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
441 which, among other things, may be used to provide connection IDs for specific
442 GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
443 case, 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
445 connection IDs need to be provided by device drivers.
447 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
450 Interacting With the Legacy GPIO Subsystem
451 ==========================================
452 Many kernel subsystems and drivers still handle GPIOs using the legacy
453 integer-based interface. It is strongly recommended to update these to the new
454 gpiod interface. For cases where both interfaces need to be used, the following
455 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
458 int desc_to_gpio(const struct gpio_desc *desc)
459 struct gpio_desc *gpio_to_desc(unsigned gpio)
461 The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
462 the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
463 All the same, a GPIO number passed to gpio_to_desc() must first be properly
464 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
465 considered valid until that GPIO number is released using gpio_free().
467 Freeing a GPIO obtained by one API with the other API is forbidden and an