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.
81 (see board.txt), 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
109 For a function using multiple GPIOs all of those can be obtained with one call::
115 This function returns a struct gpio_descs which contains an array of
116 descriptors. It also contains a pointer to a gpiolib private structure which,
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::
167 It is strictly forbidden to use a descriptor after calling these functions.
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
190 The return value is zero for success, else a negative errno. It should be
192 is possible. You should normally issue these calls from a task context. However,
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
237 head of a queue to transmit a command and get its response. This requires
240 Platforms that support this type of GPIO distinguish them from other GPIOs by
245 To access such GPIOs, a different set of accessors is defined::
250 Accessing such GPIOs requires a context which may sleep, for example a threaded
251 IRQ handler, and those accessors must be used instead of spinlock-safe
256 spinlock-safe calls.
262 ---------------------------------------
263 As a consumer should not have to care about the physical line level, all of the
266 This means that they check whether the GPIO is configured to be active low,
272 switch their output to a high impedance value. The consumer should not need to
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
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
324 Note that these functions should only be used with great moderation; a driver
328 Access multiple GPIOs with a single function call
329 -------------------------------------------------
368 corresponding chip driver. In that case a significantly improved performance
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
378 a bitmap of values to assign to the GPIOs (set)
386 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
387 my_gpio_descs->info, my_gpio_value_bitmap);
389 It is also possible to access a completely arbitrary array of descriptors. The
399 match hardware pin numbers of a single chip. If an array passed to a get/set
401 associated with the array is also passed, the function may take a fast 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::
419 It will return an IRQ number, or a negative errno code if the mapping can't be
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
440 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
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