Lines Matching +full:a +full:- +full:gpio
2 GPIO Descriptor Consumer Interface
5 This document describes the consumer interface of the GPIO framework.
11 Drivers that can't work without standard GPIO calls should have Kconfig entries
12 that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
15 #include <linux/gpio/consumer.h>
21 - Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
25 - Truly optional GPIOLIB support - where the driver does not really make use
26 of the GPIOs on certain compile-time configurations for certain systems, but
27 will use it under other compile-time configurations. In this case the
31 ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird
35 All the functions that work with the descriptor-based GPIO interface are
39 <linux/gpio/consumer.h> and descriptors exclusively.
45 With the descriptor-based interface, GPIOs are identified with an opaque,
46 non-forgeable handler that must be obtained through a call to one of the
48 device that will use the GPIO and the function the requested GPIO is supposed to
54 If a function is implemented by using several GPIOs together (e.g. a simple LED
61 For a more detailed description of the con_id parameter in the DeviceTree case
62 see Documentation/driver-api/gpio/board.rst
64 The flags parameter is used to optionally specify a direction and initial value
65 for the GPIO. Values can be:
67 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
69 * GPIOD_IN to initialize the GPIO as input.
70 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
71 * GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
83 (see board.rst), then open drain will be enforced anyway and a warning will be
86 Both functions return either a valid GPIO descriptor, or an error code checkable
87 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
88 if and only if no GPIO has been assigned to the device/function/index triplet,
89 other error codes are used for cases where a GPIO has been assigned but an error
91 errors and an absence of GPIO for optional GPIO parameters. For the common
92 pattern where a GPIO is optional, the gpiod_get_optional() and
94 instead of -ENOENT if no GPIO has been assigned to the requested function::
108 -ENOSYS return codes. System integrators should however be careful to enable
111 For a function using multiple GPIOs all of those can be obtained with one call::
117 This function returns a struct gpio_descs which contains an array of
118 descriptors. It also contains a pointer to a gpiolib private structure which,
127 The following function returns NULL instead of -ENOENT if no GPIOs have been
134 Device-managed variants of these functions are also defined::
161 A GPIO descriptor can be disposed of using the gpiod_put() function::
169 It is strictly forbidden to use a descriptor after calling these functions.
173 The device-managed variants are, unsurprisingly::
184 -----------------
185 The first thing a driver must do with a GPIO is setting its direction. If no
186 direction-setting flags have been given to gpiod_get*(), this is done by
192 The return value is zero for success, else a negative errno. It should be
194 is possible. You should normally issue these calls from a task context. However,
195 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
201 A driver can also query the current direction of a GPIO::
207 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
212 Spinlock-Safe GPIO Access
213 -------------------------
214 Most GPIO controllers can be accessed with memory read/write instructions. Those
215 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
226 open-drain signaling and output latencies.
228 The get/set calls do not return errors because "invalid GPIO" should have been
235 GPIO Access That May Sleep
236 --------------------------
237 Some GPIO controllers must be accessed using message based buses like I2C or
238 SPI. Commands to read or write those GPIO values require waiting to get to the
239 head of a queue to transmit a command and get its response. This requires
242 Platforms that support this type of GPIO distinguish them from other GPIOs by
247 To access such GPIOs, a different set of accessors is defined::
252 Accessing such GPIOs requires a context which may sleep, for example a threaded
253 IRQ handler, and those accessors must be used instead of spinlock-safe
258 spinlock-safe calls.
264 ---------------------------------------
265 As a consumer should not have to care about the physical line level, all of the
268 This means that they check whether the GPIO is configured to be active low,
274 switch their output to a high impedance value. The consumer should not need to
281 As an example, if the active low property for a dedicated GPIO is set, and the
300 but it should be avoided as much as possible, especially by system-agnostic drivers
305 Accessing raw GPIO values
306 -------------------------
307 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
308 their device will actually receive, no matter what lies between it and the GPIO
311 The following set of calls ignore the active-low or open drain property of a GPIO and
320 The active low state of a GPIO can also be queried and toggled using the
326 Note that these functions should only be used with great moderation; a driver
330 Access multiple GPIOs with a single function call
331 -------------------------------------------------
370 corresponding chip driver. In that case a significantly improved performance
376 * array_size - the number of array elements
377 * desc_array - an array of GPIO descriptors
378 * array_info - optional information obtained from gpiod_get_array()
379 * value_bitmap - a bitmap to store the GPIOs' values (get) or
380 a bitmap of values to assign to the GPIOs (set)
388 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
389 my_gpio_descs->info, my_gpio_value_bitmap);
391 It is also possible to access a completely arbitrary array of descriptors. The
401 match hardware pin numbers of a single chip. If an array passed to a get/set
403 associated with the array is also passed, the function may take a fast bitmap
405 .get/set_multiple() callback of the chip. That allows for utilization of GPIO
410 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
415 --------------------
416 GPIO lines can quite often be used as IRQs. You can get the IRQ number
417 corresponding to a given GPIO using the following call::
421 It will return an IRQ number, or a negative errno code if the mapping can't be
422 done (most likely because that particular GPIO cannot be used as IRQ). It is an
423 unchecked error to use a GPIO that wasn't set up as an input using
427 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
429 by the board-specific initialization code. Note that IRQ trigger options are
442 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
445 case, it will be handled by the GPIO subsystem automatically. However, if the
446 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
449 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
452 Interacting With the Legacy GPIO Subsystem
455 integer-based interface. It is strongly recommended to update these to the new
457 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
458 and vice-versa::
461 struct gpio_desc *gpio_to_desc(unsigned gpio)
463 The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
464 the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
465 All the same, a GPIO number passed to gpio_to_desc() must first be properly
466 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
467 considered valid until that GPIO number is released using gpio_free().
469 Freeing a GPIO obtained by one API with the other API is forbidden and an