1 GPIO Descriptor Consumer Interface
2 ==================================
4 This document describes the consumer interface of the GPIO framework. Note that
5 it describes the new descriptor-based interface. For a description of the
6 deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
9 Guidelines for GPIOs consumers
10 ==============================
12 Drivers that can't work without standard GPIO calls should have Kconfig entries
13 that depend on GPIOLIB. The functions that allow a driver to obtain and use
14 GPIOs are available by including the following file:
16 #include <linux/gpio/consumer.h>
18 All the functions that work with the descriptor-based GPIO interface are
19 prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
20 other function in the kernel should use these prefixes.
23 Obtaining and Disposing GPIOs
24 =============================
26 With the descriptor-based interface, GPIOs are identified with an opaque,
27 non-forgeable handler that must be obtained through a call to one of the
28 gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
29 device that will use the GPIO and the function the requested GPIO is supposed to
32 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
33 enum gpiod_flags flags)
35 If a function is implemented by using several GPIOs together (e.g. a simple LED
36 device that displays digits), an additional index argument can be specified:
38 struct gpio_desc *gpiod_get_index(struct device *dev,
39 const char *con_id, unsigned int idx,
40 enum gpiod_flags flags)
42 The flags parameter is used to optionally specify a direction and initial value
43 for the GPIO. Values can be:
45 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
46 later with one of the dedicated functions.
47 * GPIOD_IN to initialize the GPIO as input.
48 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
49 * GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
51 Both functions return either a valid GPIO descriptor, or an error code checkable
52 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
53 if and only if no GPIO has been assigned to the device/function/index triplet,
54 other error codes are used for cases where a GPIO has been assigned but an error
55 occurred while trying to acquire it. This is useful to discriminate between mere
56 errors and an absence of GPIO for optional GPIO parameters. For the common
57 pattern where a GPIO is optional, the gpiod_get_optional() and
58 gpiod_get_index_optional() functions can be used. These functions return NULL
59 instead of -ENOENT if no GPIO has been assigned to the requested function:
61 struct gpio_desc *gpiod_get_optional(struct device *dev,
63 enum gpiod_flags flags)
65 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
68 enum gpiod_flags flags)
70 For a function using multiple GPIOs all of those can be obtained with one call:
72 struct gpio_descs *gpiod_get_array(struct device *dev,
74 enum gpiod_flags flags)
76 This function returns a struct gpio_descs which contains an array of
81 struct gpio_desc *desc[];
84 The following function returns NULL instead of -ENOENT if no GPIOs have been
85 assigned to the requested function:
87 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
89 enum gpiod_flags flags)
91 Device-managed variants of these functions are also defined:
93 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
94 enum gpiod_flags flags)
96 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
99 enum gpiod_flags flags)
101 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
103 enum gpiod_flags flags)
105 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
108 enum gpiod_flags flags)
110 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
112 enum gpiod_flags flags)
114 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
116 enum gpiod_flags flags)
118 A GPIO descriptor can be disposed of using the gpiod_put() function:
120 void gpiod_put(struct gpio_desc *desc)
122 For an array of GPIOs this function can be used:
124 void gpiod_put_array(struct gpio_descs *descs)
126 It is strictly forbidden to use a descriptor after calling these functions.
127 It is also not allowed to individually release descriptors (using gpiod_put())
128 from an array acquired with gpiod_get_array().
130 The device-managed variants are, unsurprisingly:
132 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
134 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
142 The first thing a driver must do with a GPIO is setting its direction. If no
143 direction-setting flags have been given to gpiod_get*(), this is done by
144 invoking one of the gpiod_direction_*() functions:
146 int gpiod_direction_input(struct gpio_desc *desc)
147 int gpiod_direction_output(struct gpio_desc *desc, int value)
149 The return value is zero for success, else a negative errno. It should be
150 checked, since the get/set calls don't return errors and since misconfiguration
151 is possible. You should normally issue these calls from a task context. However,
152 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
153 of early board setup.
155 For output GPIOs, the value provided becomes the initial output value. This
156 helps avoid signal glitching during system startup.
158 A driver can also query the current direction of a GPIO:
160 int gpiod_get_direction(const struct gpio_desc *desc)
162 This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.
164 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
165 without setting its direction first is illegal and will result in undefined
169 Spinlock-Safe GPIO Access
170 -------------------------
171 Most GPIO controllers can be accessed with memory read/write instructions. Those
172 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
173 handlers and similar contexts.
175 Use the following calls to access GPIOs from an atomic context:
177 int gpiod_get_value(const struct gpio_desc *desc);
178 void gpiod_set_value(struct gpio_desc *desc, int value);
180 The values are boolean, zero for low, nonzero for high. When reading the value
181 of an output pin, the value returned should be what's seen on the pin. That
182 won't always match the specified output value, because of issues including
183 open-drain signaling and output latencies.
185 The get/set calls do not return errors because "invalid GPIO" should have been
186 reported earlier from gpiod_direction_*(). However, note that not all platforms
187 can read the value of output pins; those that can't should always return zero.
188 Also, using these calls for GPIOs that can't safely be accessed without sleeping
189 (see below) is an error.
192 GPIO Access That May Sleep
193 --------------------------
194 Some GPIO controllers must be accessed using message based buses like I2C or
195 SPI. Commands to read or write those GPIO values require waiting to get to the
196 head of a queue to transmit a command and get its response. This requires
197 sleeping, which can't be done from inside IRQ handlers.
199 Platforms that support this type of GPIO distinguish them from other GPIOs by
200 returning nonzero from this call:
202 int gpiod_cansleep(const struct gpio_desc *desc)
204 To access such GPIOs, a different set of accessors is defined:
206 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
207 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
209 Accessing such GPIOs requires a context which may sleep, for example a threaded
210 IRQ handler, and those accessors must be used instead of spinlock-safe
211 accessors without the cansleep() name suffix.
213 Other than the fact that these accessors might sleep, and will work on GPIOs
214 that can't be accessed from hardIRQ handlers, these calls act the same as the
218 Active-low State and Raw GPIO Values
219 ------------------------------------
220 Device drivers like to manage the logical state of a GPIO, i.e. the value their
221 device will actually receive, no matter what lies between it and the GPIO line.
222 In some cases, it might make sense to control the actual GPIO line value. The
223 following set of calls ignore the active-low property of a GPIO and work on the
226 int gpiod_get_raw_value(const struct gpio_desc *desc)
227 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
228 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
229 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
230 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
232 The active-low state of a GPIO can also be queried using the following call:
234 int gpiod_is_active_low(const struct gpio_desc *desc)
236 Note that these functions should only be used with great moderation ; a driver
237 should not have to care about the physical line level.
240 The active-low property
241 -----------------------
243 As a driver should not have to care about the physical line level, all of the
244 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
245 the *logical* value. With this they take the active-low property into account.
246 This means that they check whether the GPIO is configured to be active-low,
247 and if so, they manipulate the passed value before the physical line level is
250 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
251 parameter "value" as "active" ("1") or "inactive" ("0"). The physical line
252 level will be driven accordingly.
254 As an example, if the active-low property for a dedicated GPIO is set, and the
255 gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
260 Function (example) active-low proporty physical line
261 gpiod_set_raw_value(desc, 0); don't care low
262 gpiod_set_raw_value(desc, 1); don't care high
263 gpiod_set_value(desc, 0); default (active-high) low
264 gpiod_set_value(desc, 1); default (active-high) high
265 gpiod_set_value(desc, 0); active-low high
266 gpiod_set_value(desc, 1); active-low low
268 Please note again that the set_raw/get_raw functions should be avoided as much
269 as possible, especially by drivers which should not care about the actual
270 physical line level and worry about the logical value instead.
273 Set multiple GPIO outputs with a single function call
274 -----------------------------------------------------
275 The following functions set the output values of an array of GPIOs:
277 void gpiod_set_array_value(unsigned int array_size,
278 struct gpio_desc **desc_array,
280 void gpiod_set_raw_array_value(unsigned int array_size,
281 struct gpio_desc **desc_array,
283 void gpiod_set_array_value_cansleep(unsigned int array_size,
284 struct gpio_desc **desc_array,
286 void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
287 struct gpio_desc **desc_array,
290 The array can be an arbitrary set of GPIOs. The functions will try to set
291 GPIOs belonging to the same bank or chip simultaneously if supported by the
292 corresponding chip driver. In that case a significantly improved performance
293 can be expected. If simultaneous setting is not possible the GPIOs will be set
296 The gpiod_set_array() functions take three arguments:
297 * array_size - the number of array elements
298 * desc_array - an array of GPIO descriptors
299 * value_array - an array of values to assign to the GPIOs
301 The descriptor array can be obtained using the gpiod_get_array() function
302 or one of its variants. If the group of descriptors returned by that function
303 matches the desired group of GPIOs, those GPIOs can be set by simply using
304 the struct gpio_descs returned by gpiod_get_array():
306 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
307 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
310 It is also possible to set a completely arbitrary array of descriptors. The
311 descriptors may be obtained using any combination of gpiod_get() and
312 gpiod_get_array(). Afterwards the array of descriptors has to be setup
313 manually before it can be used with gpiod_set_array().
315 Note that for optimal performance GPIOs belonging to the same chip should be
316 contiguous within the array of descriptors.
321 GPIO lines can quite often be used as IRQs. You can get the IRQ number
322 corresponding to a given GPIO using the following call:
324 int gpiod_to_irq(const struct gpio_desc *desc)
326 It will return an IRQ number, or a negative errno code if the mapping can't be
327 done (most likely because that particular GPIO cannot be used as IRQ). It is an
328 unchecked error to use a GPIO that wasn't set up as an input using
329 gpiod_direction_input(), or to use an IRQ number that didn't originally come
330 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
332 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
333 free_irq(). They will often be stored into IRQ resources for platform devices,
334 by the board-specific initialization code. Note that IRQ trigger options are
335 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
342 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
343 the _CRS configuration objects of devices. Those resources do not provide
344 connection IDs (names) for GPIOs, so it is necessary to use an additional
345 mechanism for this purpose.
347 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
348 which, among other things, may be used to provide connection IDs for specific
349 GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
350 case, it will be handled by the GPIO subsystem automatically. However, if the
351 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
352 connection IDs need to be provided by device drivers.
354 For details refer to Documentation/acpi/gpio-properties.txt
357 Interacting With the Legacy GPIO Subsystem
358 ==========================================
359 Many kernel subsystems still handle GPIOs using the legacy integer-based
360 interface. Although it is strongly encouraged to upgrade them to the safer
361 descriptor-based API, the following two functions allow you to convert a GPIO
362 descriptor into the GPIO integer namespace and vice-versa:
364 int desc_to_gpio(const struct gpio_desc *desc)
365 struct gpio_desc *gpio_to_desc(unsigned gpio)
367 The GPIO number returned by desc_to_gpio() can be safely used as long as the
368 GPIO descriptor has not been freed. All the same, a GPIO number passed to
369 gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
370 descriptor is only possible after the GPIO number has been released.
372 Freeing a GPIO obtained by one API with the other API is forbidden and an