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
35   some open coding of error handling should be expected when you do this.
37 All the functions that work with the descriptor-based GPIO interface are
41 <linux/gpio/consumer.h> and descriptors exclusively.
47 With the descriptor-based interface, GPIOs are identified with an opaque,
48 non-forgeable handler that must be obtained through a call to one of the
50 device that will use the GPIO and the function the requested GPIO is supposed to
64 see Documentation/driver-api/gpio/board.rst
67 for the GPIO. Values can be:
69 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
71 * GPIOD_IN to initialize the GPIO as input.
72 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
73 * GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
75   to be electrically used with open drain.
77   to be electrically used with open drain.
83 The two last flags are used for use cases where open drain is mandatory, such
84 as I2C: if the line is not already configured as open drain in the mappings
85 (see board.rst), then open drain will be enforced anyway and a warning will be
88 Both functions return either a valid GPIO descriptor, or an error code checkable
89 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
90 if and only if no GPIO has been assigned to the device/function/index triplet,
91 other error codes are used for cases where a GPIO has been assigned but an error
93 errors and an absence of GPIO for optional GPIO parameters. For the common
94 pattern where a GPIO is optional, the gpiod_get_optional() and
96 instead of -ENOENT if no GPIO has been assigned to the requested function::
110 -ENOSYS return codes.  System integrators should however be careful to enable
129 The following function returns NULL instead of -ENOENT if no GPIOs have been
136 Device-managed variants of these functions are also defined::
163 A GPIO descriptor can be disposed of using the gpiod_put() function::
175 The device-managed variants are, unsurprisingly::
186 -----------------
187 The first thing a driver must do with a GPIO is setting its direction. If no
188 direction-setting flags have been given to gpiod_get*(), this is done by
197 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
203 A driver can also query the current direction of a GPIO::
209 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
214 Spinlock-Safe GPIO Access
215 -------------------------
216 Most GPIO controllers can be accessed with memory read/write instructions. Those
217 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
228 open-drain signaling and output latencies.
230 The get/set calls do not return errors because "invalid GPIO" should have been
237 GPIO Access That May Sleep
238 --------------------------
239 Some GPIO controllers must be accessed using message based buses like I2C or
240 SPI. Commands to read or write those GPIO values require waiting to get to the
244 Platforms that support this type of GPIO distinguish them from other GPIOs by
255 IRQ handler, and those accessors must be used instead of spinlock-safe
260 spinlock-safe calls.
265 The active low and open drain semantics
266 ---------------------------------------
270 This means that they check whether the GPIO is configured to be active low,
274 The same is applicable for open drain or open source output lines: those do not
275 actively drive their output high (open drain) or low (open source), they just
277 care. (For details read about open drain in driver.rst.)
280 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
283 As an example, if the active low property for a dedicated GPIO is set, and the
296   gpiod_set_value(desc, 0);          open drain             low
297   gpiod_set_value(desc, 1);          open drain             high impedance
298   gpiod_set_value(desc, 0);          open source            high impedance
299   gpiod_set_value(desc, 1);          open source            high
302 but it should be avoided as much as possible, especially by system-agnostic drivers
307 Accessing raw GPIO values
308 -------------------------
309 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
310 their device will actually receive, no matter what lies between it and the GPIO
313 The following set of calls ignore the active-low or open drain property of a GPIO and
322 The active low state of a GPIO can also be queried and toggled using the
329 should not have to care about the physical line level or open drain semantics.
333 -------------------------------------------------
378 	* array_size	- the number of array elements
379 	* desc_array	- an array of GPIO descriptors
380 	* array_info	- optional information obtained from gpiod_get_array()
381 	* value_bitmap	- a bitmap to store the GPIOs' values (get) or
390 	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
391 			      my_gpio_descs->info, my_gpio_value_bitmap);
407 .get/set_multiple() callback of the chip.  That allows for utilization of GPIO
412 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
417 --------------------
418 GPIO lines can quite often be used as IRQs. You can get the IRQ number
419 corresponding to a given GPIO using the following call::
424 done (most likely because that particular GPIO cannot be used as IRQ). It is an
425 unchecked error to use a GPIO that wasn't set up as an input using
429 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
431 by the board-specific initialization code. Note that IRQ trigger options are
447 case, it will be handled by the GPIO subsystem automatically.  However, if the
448 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
451 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
454 Interacting With the Legacy GPIO Subsystem
457 integer-based interface. It is strongly recommended to update these to the new
459 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
460 and vice-versa::
463 	struct gpio_desc *gpio_to_desc(unsigned gpio)
465 The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
466 the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
467 All the same, a GPIO number passed to gpio_to_desc() must first be properly
468 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
469 considered valid until that GPIO number is released using gpio_free().
471 Freeing a GPIO obtained by one API with the other API is forbidden and an