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 legacy.rst.
13 Drivers that can't work without standard GPIO calls should have Kconfig entries
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
60 see Documentation/driver-api/gpio/board.rst
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.
71   to be electrically used with open drain.
73   to be electrically used with open drain.
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.rst), then open drain will be enforced anyway and a warning will be
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
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
92 instead of -ENOENT if no GPIO has been assigned to the requested function::
106 -ENOSYS return codes.  System integrators should however be careful to enable
125 The following function returns NULL instead of -ENOENT if no GPIOs have been
132 Device-managed variants of these functions are also defined::
159 A GPIO descriptor can be disposed of using the gpiod_put() function::
171 The device-managed variants are, unsurprisingly::
182 -----------------
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
193 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
199 A driver can also query the current direction of a GPIO::
205 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
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
224 open-drain signaling and output latencies.
226 The get/set calls do not return errors because "invalid GPIO" should have been
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
240 Platforms that support this type of GPIO distinguish them from other GPIOs by
251 IRQ handler, and those accessors must be used instead of spinlock-safe
256 spinlock-safe calls.
261 The active low and open drain semantics
262 ---------------------------------------
266 This means that they check whether the GPIO is configured to be active low,
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
273 care. (For details read about open drain in driver.rst.)
276 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
279 As an example, if the active low property for a dedicated GPIO is set, and the
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
298 but it should be avoided as much as possible, especially by system-agnostic drivers
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
318 The active low state of a GPIO can also be queried and toggled using the
325 should not have to care about the physical line level or open drain semantics.
329 -------------------------------------------------
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
386 	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
387 			      my_gpio_descs->info, my_gpio_value_bitmap);
403 .get/set_multiple() callback of the chip.  That allows for utilization of GPIO
408 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
413 --------------------
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::
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
425 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
427 by the board-specific initialization code. Note that IRQ trigger options are
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
447 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
450 Interacting With the Legacy GPIO Subsystem
453 integer-based interface. It is strongly recommended to update these to the new
455 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
456 and vice-versa::
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