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
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.
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
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
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::
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
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
236 Platforms that support this type of GPIO distinguish them from other GPIOs by
247 IRQ handler, and those accessors must be used instead of spinlock-safe
252 spinlock-safe calls.
255 The active low and open drain semantics
256 ---------------------------------------
260 This means that they check whether the GPIO is configured to be active low,
264 The same is applicable for open drain or open source output lines: those do not
265 actively drive their output high (open drain) or low (open source), they just
267 care. (For details read about open drain in driver.txt.)
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
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
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::
317 should not have to care about the physical line level or open drain semantics.
321 -------------------------------------------------
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
377 	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
378 			      my_gpio_descs->info, my_gpio_value_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::
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
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