Lines Matching +full:a +full:- +full:gpio
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
119 The following function returns NULL instead of -ENOENT if no GPIOs have been
126 Device-managed variants of these functions are also defined::
153 A GPIO descriptor can be disposed of using the gpiod_put() function::
161 It is strictly forbidden to use a descriptor after calling these functions.
165 The device-managed variants are, unsurprisingly::
176 -----------------
177 The first thing a driver must do with a GPIO is setting its direction. If no
178 direction-setting flags have been given to gpiod_get*(), this is done by
184 The return value is zero for success, else a negative errno. It should be
186 is possible. You should normally issue these calls from a task context. However,
187 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
193 A driver can also query the current direction of a GPIO::
199 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
204 Spinlock-Safe GPIO Access
205 -------------------------
206 Most GPIO controllers can be accessed with memory read/write instructions. Those
207 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
218 open-drain signaling and output latencies.
220 The get/set calls do not return errors because "invalid GPIO" should have been
227 GPIO Access That May Sleep
228 --------------------------
229 Some GPIO controllers must be accessed using message based buses like I2C or
230 SPI. Commands to read or write those GPIO values require waiting to get to the
231 head of a queue to transmit a command and get its response. This requires
234 Platforms that support this type of GPIO distinguish them from other GPIOs by
239 To access such GPIOs, a different set of accessors is defined::
244 Accessing such GPIOs requires a context which may sleep, for example a threaded
245 IRQ handler, and those accessors must be used instead of spinlock-safe
250 spinlock-safe calls.
254 ---------------------------------------
255 As a consumer should not have to care about the physical line level, all of the
258 This means that they check whether the GPIO is configured to be active low,
264 switch their output to a high impedance value. The consumer should not need to
268 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
271 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 -------------------------------------------------
352 corresponding chip driver. In that case a significantly improved performance
357 * array_size - the number of array elements
358 * desc_array - an array of GPIO descriptors
359 * value_array - an array to store the GPIOs' values (get) or
368 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
371 It is also possible to access a completely arbitrary array of descriptors. The
381 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
386 --------------------
387 GPIO lines can quite often be used as IRQs. You can get the IRQ number
388 corresponding to a given GPIO using the following call::
392 It will return an IRQ number, or a negative errno code if the mapping can't be
393 done (most likely because that particular GPIO cannot be used as IRQ). It is an
394 unchecked error to use a GPIO that wasn't set up as an input using
398 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
400 by the board-specific initialization code. Note that IRQ trigger options are
413 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
416 case, it will be handled by the GPIO subsystem automatically. However, if the
417 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
420 For details refer to Documentation/acpi/gpio-properties.txt
423 Interacting With the Legacy GPIO Subsystem
425 Many kernel subsystems still handle GPIOs using the legacy integer-based
427 descriptor-based API, the following two functions allow you to convert a GPIO
428 descriptor into the GPIO integer namespace and vice-versa::
431 struct gpio_desc *gpio_to_desc(unsigned gpio)
433 The GPIO number returned by desc_to_gpio() can be safely used as long as the
434 GPIO descriptor has not been freed. All the same, a GPIO number passed to
435 gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
436 descriptor is only possible after the GPIO number has been released.
438 Freeing a GPIO obtained by one API with the other API is forbidden and an