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 The two last flags are used for use cases where open drain is mandatory, such
76 as I2C: if the line is not already configured as open drain in the mappings
77 (see board.txt), then open drain will be enforced anyway and a warning will be
78 printed that the board configuration needs to be updated to match the use case.
80 Both functions return either a valid GPIO descriptor, or an error code checkable
81 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
82 if and only if no GPIO has been assigned to the device/function/index triplet,
83 other error codes are used for cases where a GPIO has been assigned but an error
84 occurred while trying to acquire it. This is useful to discriminate between mere
85 errors and an absence of GPIO for optional GPIO parameters. For the common
86 pattern where a GPIO is optional, the gpiod_get_optional() and
87 gpiod_get_index_optional() functions can be used. These functions return NULL
88 instead of -ENOENT if no GPIO has been assigned to the requested function::
90 struct gpio_desc *gpiod_get_optional(struct device *dev,
92 enum gpiod_flags flags)
94 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
97 enum gpiod_flags flags)
99 Note that gpio_get*_optional() functions (and their managed variants), unlike
100 the rest of gpiolib API, also return NULL when gpiolib support is disabled.
101 This is helpful to driver authors, since they do not need to special case
102 -ENOSYS return codes. System integrators should however be careful to enable
103 gpiolib on systems that need it.
105 For a function using multiple GPIOs all of those can be obtained with one call::
107 struct gpio_descs *gpiod_get_array(struct device *dev,
109 enum gpiod_flags flags)
111 This function returns a struct gpio_descs which contains an array of
116 struct gpio_desc *desc[];
119 The following function returns NULL instead of -ENOENT if no GPIOs have been
120 assigned to the requested function::
122 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
124 enum gpiod_flags flags)
126 Device-managed variants of these functions are also defined::
128 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
129 enum gpiod_flags flags)
131 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
134 enum gpiod_flags flags)
136 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
138 enum gpiod_flags flags)
140 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
143 enum gpiod_flags flags)
145 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
147 enum gpiod_flags flags)
149 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
151 enum gpiod_flags flags)
153 A GPIO descriptor can be disposed of using the gpiod_put() function::
155 void gpiod_put(struct gpio_desc *desc)
157 For an array of GPIOs this function can be used::
159 void gpiod_put_array(struct gpio_descs *descs)
161 It is strictly forbidden to use a descriptor after calling these functions.
162 It is also not allowed to individually release descriptors (using gpiod_put())
163 from an array acquired with gpiod_get_array().
165 The device-managed variants are, unsurprisingly::
167 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
169 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
177 The first thing a driver must do with a GPIO is setting its direction. If no
178 direction-setting flags have been given to gpiod_get*(), this is done by
179 invoking one of the gpiod_direction_*() functions::
181 int gpiod_direction_input(struct gpio_desc *desc)
182 int gpiod_direction_output(struct gpio_desc *desc, int value)
184 The return value is zero for success, else a negative errno. It should be
185 checked, since the get/set calls don't return errors and since misconfiguration
186 is possible. You should normally issue these calls from a task context. However,
187 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
188 of early board setup.
190 For output GPIOs, the value provided becomes the initial output value. This
191 helps avoid signal glitching during system startup.
193 A driver can also query the current direction of a GPIO::
195 int gpiod_get_direction(const struct gpio_desc *desc)
197 This function returns 0 for output, 1 for input, or an error code in case of error.
199 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
200 without setting its direction first is illegal and will result in undefined
204 Spinlock-Safe GPIO Access
205 -------------------------
206 Most GPIO controllers can be accessed with memory read/write instructions. Those
207 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
208 handlers and similar contexts.
210 Use the following calls to access GPIOs from an atomic context::
212 int gpiod_get_value(const struct gpio_desc *desc);
213 void gpiod_set_value(struct gpio_desc *desc, int value);
215 The values are boolean, zero for low, nonzero for high. When reading the value
216 of an output pin, the value returned should be what's seen on the pin. That
217 won't always match the specified output value, because of issues including
218 open-drain signaling and output latencies.
220 The get/set calls do not return errors because "invalid GPIO" should have been
221 reported earlier from gpiod_direction_*(). However, note that not all platforms
222 can read the value of output pins; those that can't should always return zero.
223 Also, using these calls for GPIOs that can't safely be accessed without sleeping
224 (see below) is an error.
227 GPIO Access That May Sleep
228 --------------------------
229 Some GPIO controllers must be accessed using message based buses like I2C or
230 SPI. Commands to read or write those GPIO values require waiting to get to the
231 head of a queue to transmit a command and get its response. This requires
232 sleeping, which can't be done from inside IRQ handlers.
234 Platforms that support this type of GPIO distinguish them from other GPIOs by
235 returning nonzero from this call::
237 int gpiod_cansleep(const struct gpio_desc *desc)
239 To access such GPIOs, a different set of accessors is defined::
241 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
242 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
244 Accessing such GPIOs requires a context which may sleep, for example a threaded
245 IRQ handler, and those accessors must be used instead of spinlock-safe
246 accessors without the cansleep() name suffix.
248 Other than the fact that these accessors might sleep, and will work on GPIOs
249 that can't be accessed from hardIRQ handlers, these calls act the same as the
253 The active low and open drain semantics
254 ---------------------------------------
255 As a consumer should not have to care about the physical line level, all of the
256 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
257 the *logical* value. With this they take the active low property into account.
258 This means that they check whether the GPIO is configured to be active low,
259 and if so, they manipulate the passed value before the physical line level is
262 The same is applicable for open drain or open source output lines: those do not
263 actively drive their output high (open drain) or low (open source), they just
264 switch their output to a high impedance value. The consumer should not need to
265 care. (For details read about open drain in driver.txt.)
267 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
268 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
269 level will be driven accordingly.
271 As an example, if the active low property for a dedicated GPIO is set, and the
272 gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
277 Function (example) line property physical line
278 gpiod_set_raw_value(desc, 0); don't care low
279 gpiod_set_raw_value(desc, 1); don't care high
280 gpiod_set_value(desc, 0); default (active high) low
281 gpiod_set_value(desc, 1); default (active high) high
282 gpiod_set_value(desc, 0); active low high
283 gpiod_set_value(desc, 1); active low low
284 gpiod_set_value(desc, 0); default (active high) low
285 gpiod_set_value(desc, 1); default (active high) high
286 gpiod_set_value(desc, 0); open drain low
287 gpiod_set_value(desc, 1); open drain high impedance
288 gpiod_set_value(desc, 0); open source high impedance
289 gpiod_set_value(desc, 1); open source high
291 It is possible to override these semantics using the set_raw/get_raw functions
292 but it should be avoided as much as possible, especially by system-agnostic drivers
293 which should not need to care about the actual physical line level and worry about
294 the logical value instead.
297 Accessing raw GPIO values
298 -------------------------
299 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
300 their device will actually receive, no matter what lies between it and the GPIO
303 The following set of calls ignore the active-low or open drain property of a GPIO and
304 work on the raw line value::
306 int gpiod_get_raw_value(const struct gpio_desc *desc)
307 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
308 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
309 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
310 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
312 The active low state of a GPIO can also be queried using the following call::
314 int gpiod_is_active_low(const struct gpio_desc *desc)
316 Note that these functions should only be used with great moderation; a driver
317 should not have to care about the physical line level or open drain semantics.
320 Access multiple GPIOs with a single function call
321 -------------------------------------------------
322 The following functions get or set the values of an array of GPIOs::
324 int gpiod_get_array_value(unsigned int array_size,
325 struct gpio_desc **desc_array,
327 int gpiod_get_raw_array_value(unsigned int array_size,
328 struct gpio_desc **desc_array,
330 int gpiod_get_array_value_cansleep(unsigned int array_size,
331 struct gpio_desc **desc_array,
333 int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
334 struct gpio_desc **desc_array,
337 void gpiod_set_array_value(unsigned int array_size,
338 struct gpio_desc **desc_array,
340 void gpiod_set_raw_array_value(unsigned int array_size,
341 struct gpio_desc **desc_array,
343 void gpiod_set_array_value_cansleep(unsigned int array_size,
344 struct gpio_desc **desc_array,
346 void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
347 struct gpio_desc **desc_array,
350 The array can be an arbitrary set of GPIOs. The functions will try to access
351 GPIOs belonging to the same bank or chip simultaneously if supported by the
352 corresponding chip driver. In that case a significantly improved performance
353 can be expected. If simultaneous access is not possible the GPIOs will be
354 accessed sequentially.
356 The functions take three arguments:
357 * array_size - the number of array elements
358 * desc_array - an array of GPIO descriptors
359 * value_array - an array to store the GPIOs' values (get) or
360 an array of values to assign to the GPIOs (set)
362 The descriptor array can be obtained using the gpiod_get_array() function
363 or one of its variants. If the group of descriptors returned by that function
364 matches the desired group of GPIOs, those GPIOs can be accessed by simply using
365 the struct gpio_descs returned by gpiod_get_array()::
367 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
368 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
371 It is also possible to access a completely arbitrary array of descriptors. The
372 descriptors may be obtained using any combination of gpiod_get() and
373 gpiod_get_array(). Afterwards the array of descriptors has to be setup
374 manually before it can be passed to one of the above functions.
376 Note that for optimal performance GPIOs belonging to the same chip should be
377 contiguous within the array of descriptors.
379 The return value of gpiod_get_array_value() and its variants is 0 on success
380 or negative on error. Note the difference to gpiod_get_value(), which returns
381 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
382 values are stored in value_array rather than passed back as return value.
387 GPIO lines can quite often be used as IRQs. You can get the IRQ number
388 corresponding to a given GPIO using the following call::
390 int gpiod_to_irq(const struct gpio_desc *desc)
392 It will return an IRQ number, or a negative errno code if the mapping can't be
393 done (most likely because that particular GPIO cannot be used as IRQ). It is an
394 unchecked error to use a GPIO that wasn't set up as an input using
395 gpiod_direction_input(), or to use an IRQ number that didn't originally come
396 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
398 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
399 free_irq(). They will often be stored into IRQ resources for platform devices,
400 by the board-specific initialization code. Note that IRQ trigger options are
401 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
408 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
409 the _CRS configuration objects of devices. Those resources do not provide
410 connection IDs (names) for GPIOs, so it is necessary to use an additional
411 mechanism for this purpose.
413 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
414 which, among other things, may be used to provide connection IDs for specific
415 GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
416 case, it will be handled by the GPIO subsystem automatically. However, if the
417 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
418 connection IDs need to be provided by device drivers.
420 For details refer to Documentation/acpi/gpio-properties.txt
423 Interacting With the Legacy GPIO Subsystem
424 ==========================================
425 Many kernel subsystems still handle GPIOs using the legacy integer-based
426 interface. Although it is strongly encouraged to upgrade them to the safer
427 descriptor-based API, the following two functions allow you to convert a GPIO
428 descriptor into the GPIO integer namespace and vice-versa::
430 int desc_to_gpio(const struct gpio_desc *desc)
431 struct gpio_desc *gpio_to_desc(unsigned gpio)
433 The GPIO number returned by desc_to_gpio() can be safely used as long as the
434 GPIO descriptor has not been freed. All the same, a GPIO number passed to
435 gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
436 descriptor is only possible after the GPIO number has been released.
438 Freeing a GPIO obtained by one API with the other API is forbidden and an