driver-api/gpio/consumer.rst

2 GPIO Descriptor Consumer Interface
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.
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
17 	#include <linux/gpio/consumer.h>
23 - Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
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
33 All the functions that work with the descriptor-based GPIO interface are
37 <linux/gpio/consumer.h> and descriptors exclusively.
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
46 device that will use the GPIO and the function the requested GPIO is supposed to
52 If a function is implemented by using several GPIOs together (e.g. a simple LED
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
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.
77 (see board.txt), then open drain will be enforced anyway and a warning will be
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
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
88 instead of -ENOENT if no GPIO has been assigned to the requested function::
102 -ENOSYS return codes.  System integrators should however be careful to enable
105 For a function using multiple GPIOs all of those can be obtained with one call::
111 This function returns a struct gpio_descs which contains an array of
112 descriptors.  It also contains a pointer to a gpiolib private structure which,
121 The following function returns NULL instead of -ENOENT if no GPIOs have been
128 Device-managed variants of these functions are also defined::
155 A GPIO descriptor can be disposed of using the gpiod_put() function::
163 It is strictly forbidden to use a descriptor after calling these functions.
167 The device-managed variants are, unsurprisingly::
178 -----------------
179 The first thing a driver must do with a GPIO is setting its direction. If no
180 direction-setting flags have been given to gpiod_get*(), this is done by
186 The return value is zero for success, else a negative errno. It should be
188 is possible. You should normally issue these calls from a task context. However,
189 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
195 A driver can also query the current direction of a GPIO::
201 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
206 Spinlock-Safe GPIO Access
207 -------------------------
208 Most GPIO controllers can be accessed with memory read/write instructions. Those
209 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
220 open-drain signaling and output latencies.
222 The get/set calls do not return errors because "invalid GPIO" should have been
229 GPIO Access That May Sleep
230 --------------------------
231 Some GPIO controllers must be accessed using message based buses like I2C or
232 SPI. Commands to read or write those GPIO values require waiting to get to the
233 head of a queue to transmit a command and get its response. This requires
236 Platforms that support this type of GPIO distinguish them from other GPIOs by
241 To access such GPIOs, a different set of accessors is defined::
246 Accessing such GPIOs requires a context which may sleep, for example a threaded
247 IRQ handler, and those accessors must be used instead of spinlock-safe
252 spinlock-safe calls.
256 ---------------------------------------
257 As a consumer should not have to care about the physical line level, all of the
260 This means that they check whether the GPIO is configured to be active low,
266 switch their output to a high impedance value. The consumer should not need to
270 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
273 As an example, if the active low property for a dedicated GPIO is set, and the
292 but it should be avoided as much as possible, especially by system-agnostic drivers
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
312 The active low state of a GPIO can also be queried using the following call::
316 Note that these functions should only be used with great moderation; a driver
320 Access multiple GPIOs with a single function call
321 -------------------------------------------------
360 corresponding chip driver. In that case a significantly improved performance
365 	* array_size	- the number of array elements
366 	* desc_array	- an array of GPIO descriptors
367 	* array_info	- optional information obtained from gpiod_get_array()
368 	* value_bitmap	- a bitmap to store the GPIOs' values (get) or
369 			  a bitmap of values to assign to the GPIOs (set)
377 	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
378 			      my_gpio_descs->info, my_gpio_value_bitmap);
380 It is also possible to access a completely arbitrary array of descriptors. The
390 match hardware pin numbers of a single chip.  If an array passed to a get/set
392 associated with the array is also passed, the function may take a fast bitmap
394 .get/set_multiple() callback of the chip.  That allows for utilization of GPIO
399 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
404 --------------------
405 GPIO lines can quite often be used as IRQs. You can get the IRQ number
406 corresponding to a given GPIO using the following call::
410 It will return an IRQ number, or a negative errno code if the mapping can't be
411 done (most likely because that particular GPIO cannot be used as IRQ). It is an
412 unchecked error to use a GPIO that wasn't set up as an input using
416 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
418 by the board-specific initialization code. Note that IRQ trigger options are
431 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
434 case, it will be handled by the GPIO subsystem automatically.  However, if the
435 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
438 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
441 Interacting With the Legacy GPIO Subsystem
443 Many kernel subsystems still handle GPIOs using the legacy integer-based
445 descriptor-based API, the following two functions allow you to convert a GPIO
446 descriptor into the GPIO integer namespace and vice-versa::
449 	struct gpio_desc *gpio_to_desc(unsigned gpio)
451 The GPIO number returned by desc_to_gpio() can be safely used as long as the
452 GPIO descriptor has not been freed. All the same, a GPIO number passed to
453 gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
454 descriptor is only possible after the GPIO number has been released.
456 Freeing a GPIO obtained by one API with the other API is forbidden and an