1==================================
2GPIO Descriptor Consumer Interface
3==================================
4
5This document describes the consumer interface of the GPIO framework. Note that
6it describes the new descriptor-based interface. For a description of the
7deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
8
9
10Guidelines for GPIOs consumers
11==============================
12
13Drivers that can't work without standard GPIO calls should have Kconfig entries
14that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
15obtain and use GPIOs are available by including the following file::
16
17	#include <linux/gpio/consumer.h>
18
19There are static inline stubs for all functions in the header file in the case
20where GPIOLIB is disabled. When these stubs are called they will emit
21warnings. These stubs are used for two use cases:
22
23- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
24  the current platform does not enable or select GPIOLIB because we are not
25  going to execute the system anyway.
26
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
30  consumer must make sure not to call into these functions, or the user will
31  be met with console warnings that may be perceived as intimidating.
32
33All the functions that work with the descriptor-based GPIO interface are
34prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
35interface. No other function in the kernel should use these prefixes. The use
36of the legacy functions is strongly discouraged, new code should use
37<linux/gpio/consumer.h> and descriptors exclusively.
38
39
40Obtaining and Disposing GPIOs
41=============================
42
43With the descriptor-based interface, GPIOs are identified with an opaque,
44non-forgeable handler that must be obtained through a call to one of the
45gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
46device that will use the GPIO and the function the requested GPIO is supposed to
47fulfill::
48
49	struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
50				    enum gpiod_flags flags)
51
52If a function is implemented by using several GPIOs together (e.g. a simple LED
53device that displays digits), an additional index argument can be specified::
54
55	struct gpio_desc *gpiod_get_index(struct device *dev,
56					  const char *con_id, unsigned int idx,
57					  enum gpiod_flags flags)
58
59For a more detailed description of the con_id parameter in the DeviceTree case
60see Documentation/driver-api/gpio/board.rst
61
62The flags parameter is used to optionally specify a direction and initial value
63for the GPIO. Values can be:
64
65* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
66  later with one of the dedicated functions.
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.
70* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
71  to be electrically used with open drain.
72* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
73  to be electrically used with open drain.
74
75Note that the initial value is *logical* and the physical line level depends on
76whether the line is configured active high or active low (see
77:ref:`active_low_semantics`).
78
79The two last flags are used for use cases where open drain is mandatory, such
80as I2C: if the line is not already configured as open drain in the mappings
81(see board.txt), then open drain will be enforced anyway and a warning will be
82printed that the board configuration needs to be updated to match the use case.
83
84Both functions return either a valid GPIO descriptor, or an error code checkable
85with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
86if and only if no GPIO has been assigned to the device/function/index triplet,
87other error codes are used for cases where a GPIO has been assigned but an error
88occurred while trying to acquire it. This is useful to discriminate between mere
89errors and an absence of GPIO for optional GPIO parameters. For the common
90pattern where a GPIO is optional, the gpiod_get_optional() and
91gpiod_get_index_optional() functions can be used. These functions return NULL
92instead of -ENOENT if no GPIO has been assigned to the requested function::
93
94	struct gpio_desc *gpiod_get_optional(struct device *dev,
95					     const char *con_id,
96					     enum gpiod_flags flags)
97
98	struct gpio_desc *gpiod_get_index_optional(struct device *dev,
99						   const char *con_id,
100						   unsigned int index,
101						   enum gpiod_flags flags)
102
103Note that gpio_get*_optional() functions (and their managed variants), unlike
104the rest of gpiolib API, also return NULL when gpiolib support is disabled.
105This is helpful to driver authors, since they do not need to special case
106-ENOSYS return codes.  System integrators should however be careful to enable
107gpiolib on systems that need it.
108
109For a function using multiple GPIOs all of those can be obtained with one call::
110
111	struct gpio_descs *gpiod_get_array(struct device *dev,
112					   const char *con_id,
113					   enum gpiod_flags flags)
114
115This function returns a struct gpio_descs which contains an array of
116descriptors.  It also contains a pointer to a gpiolib private structure which,
117if passed back to get/set array functions, may speed up I/O proocessing::
118
119	struct gpio_descs {
120		struct gpio_array *info;
121		unsigned int ndescs;
122		struct gpio_desc *desc[];
123	}
124
125The following function returns NULL instead of -ENOENT if no GPIOs have been
126assigned to the requested function::
127
128	struct gpio_descs *gpiod_get_array_optional(struct device *dev,
129						    const char *con_id,
130						    enum gpiod_flags flags)
131
132Device-managed variants of these functions are also defined::
133
134	struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
135					 enum gpiod_flags flags)
136
137	struct gpio_desc *devm_gpiod_get_index(struct device *dev,
138					       const char *con_id,
139					       unsigned int idx,
140					       enum gpiod_flags flags)
141
142	struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
143						  const char *con_id,
144						  enum gpiod_flags flags)
145
146	struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
147							const char *con_id,
148							unsigned int index,
149							enum gpiod_flags flags)
150
151	struct gpio_descs *devm_gpiod_get_array(struct device *dev,
152						const char *con_id,
153						enum gpiod_flags flags)
154
155	struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
156							 const char *con_id,
157							 enum gpiod_flags flags)
158
159A GPIO descriptor can be disposed of using the gpiod_put() function::
160
161	void gpiod_put(struct gpio_desc *desc)
162
163For an array of GPIOs this function can be used::
164
165	void gpiod_put_array(struct gpio_descs *descs)
166
167It is strictly forbidden to use a descriptor after calling these functions.
168It is also not allowed to individually release descriptors (using gpiod_put())
169from an array acquired with gpiod_get_array().
170
171The device-managed variants are, unsurprisingly::
172
173	void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
174
175	void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
176
177
178Using GPIOs
179===========
180
181Setting Direction
182-----------------
183The first thing a driver must do with a GPIO is setting its direction. If no
184direction-setting flags have been given to gpiod_get*(), this is done by
185invoking one of the gpiod_direction_*() functions::
186
187	int gpiod_direction_input(struct gpio_desc *desc)
188	int gpiod_direction_output(struct gpio_desc *desc, int value)
189
190The return value is zero for success, else a negative errno. It should be
191checked, since the get/set calls don't return errors and since misconfiguration
192is possible. You should normally issue these calls from a task context. However,
193for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
194of early board setup.
195
196For output GPIOs, the value provided becomes the initial output value. This
197helps avoid signal glitching during system startup.
198
199A driver can also query the current direction of a GPIO::
200
201	int gpiod_get_direction(const struct gpio_desc *desc)
202
203This function returns 0 for output, 1 for input, or an error code in case of error.
204
205Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
206without setting its direction first is illegal and will result in undefined
207behavior!**
208
209
210Spinlock-Safe GPIO Access
211-------------------------
212Most GPIO controllers can be accessed with memory read/write instructions. Those
213don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
214handlers and similar contexts.
215
216Use the following calls to access GPIOs from an atomic context::
217
218	int gpiod_get_value(const struct gpio_desc *desc);
219	void gpiod_set_value(struct gpio_desc *desc, int value);
220
221The values are boolean, zero for low, nonzero for high. When reading the value
222of an output pin, the value returned should be what's seen on the pin. That
223won't always match the specified output value, because of issues including
224open-drain signaling and output latencies.
225
226The get/set calls do not return errors because "invalid GPIO" should have been
227reported earlier from gpiod_direction_*(). However, note that not all platforms
228can read the value of output pins; those that can't should always return zero.
229Also, using these calls for GPIOs that can't safely be accessed without sleeping
230(see below) is an error.
231
232
233GPIO Access That May Sleep
234--------------------------
235Some GPIO controllers must be accessed using message based buses like I2C or
236SPI. Commands to read or write those GPIO values require waiting to get to the
237head of a queue to transmit a command and get its response. This requires
238sleeping, which can't be done from inside IRQ handlers.
239
240Platforms that support this type of GPIO distinguish them from other GPIOs by
241returning nonzero from this call::
242
243	int gpiod_cansleep(const struct gpio_desc *desc)
244
245To access such GPIOs, a different set of accessors is defined::
246
247	int gpiod_get_value_cansleep(const struct gpio_desc *desc)
248	void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
249
250Accessing such GPIOs requires a context which may sleep, for example a threaded
251IRQ handler, and those accessors must be used instead of spinlock-safe
252accessors without the cansleep() name suffix.
253
254Other than the fact that these accessors might sleep, and will work on GPIOs
255that can't be accessed from hardIRQ handlers, these calls act the same as the
256spinlock-safe calls.
257
258
259.. _active_low_semantics:
260
261The active low and open drain semantics
262---------------------------------------
263As a consumer should not have to care about the physical line level, all of the
264gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
265the *logical* value. With this they take the active low property into account.
266This means that they check whether the GPIO is configured to be active low,
267and if so, they manipulate the passed value before the physical line level is
268driven.
269
270The same is applicable for open drain or open source output lines: those do not
271actively drive their output high (open drain) or low (open source), they just
272switch their output to a high impedance value. The consumer should not need to
273care. (For details read about open drain in driver.txt.)
274
275With this, all the gpiod_set_(array)_value_xxx() functions interpret the
276parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
277level will be driven accordingly.
278
279As an example, if the active low property for a dedicated GPIO is set, and the
280gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
281will be driven low.
282
283To summarize::
284
285  Function (example)                 line property          physical line
286  gpiod_set_raw_value(desc, 0);      don't care             low
287  gpiod_set_raw_value(desc, 1);      don't care             high
288  gpiod_set_value(desc, 0);          default (active high)  low
289  gpiod_set_value(desc, 1);          default (active high)  high
290  gpiod_set_value(desc, 0);          active low             high
291  gpiod_set_value(desc, 1);          active low             low
292  gpiod_set_value(desc, 0);          open drain             low
293  gpiod_set_value(desc, 1);          open drain             high impedance
294  gpiod_set_value(desc, 0);          open source            high impedance
295  gpiod_set_value(desc, 1);          open source            high
296
297It is possible to override these semantics using the set_raw/get_raw functions
298but it should be avoided as much as possible, especially by system-agnostic drivers
299which should not need to care about the actual physical line level and worry about
300the logical value instead.
301
302
303Accessing raw GPIO values
304-------------------------
305Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
306their device will actually receive, no matter what lies between it and the GPIO
307line.
308
309The following set of calls ignore the active-low or open drain property of a GPIO and
310work on the raw line value::
311
312	int gpiod_get_raw_value(const struct gpio_desc *desc)
313	void gpiod_set_raw_value(struct gpio_desc *desc, int value)
314	int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
315	void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
316	int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
317
318The active low state of a GPIO can also be queried and toggled using the
319following calls::
320
321	int gpiod_is_active_low(const struct gpio_desc *desc)
322	void gpiod_toggle_active_low(struct gpio_desc *desc)
323
324Note that these functions should only be used with great moderation; a driver
325should not have to care about the physical line level or open drain semantics.
326
327
328Access multiple GPIOs with a single function call
329-------------------------------------------------
330The following functions get or set the values of an array of GPIOs::
331
332	int gpiod_get_array_value(unsigned int array_size,
333				  struct gpio_desc **desc_array,
334				  struct gpio_array *array_info,
335				  unsigned long *value_bitmap);
336	int gpiod_get_raw_array_value(unsigned int array_size,
337				      struct gpio_desc **desc_array,
338				      struct gpio_array *array_info,
339				      unsigned long *value_bitmap);
340	int gpiod_get_array_value_cansleep(unsigned int array_size,
341					   struct gpio_desc **desc_array,
342					   struct gpio_array *array_info,
343					   unsigned long *value_bitmap);
344	int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
345					   struct gpio_desc **desc_array,
346					   struct gpio_array *array_info,
347					   unsigned long *value_bitmap);
348
349	int gpiod_set_array_value(unsigned int array_size,
350				  struct gpio_desc **desc_array,
351				  struct gpio_array *array_info,
352				  unsigned long *value_bitmap)
353	int gpiod_set_raw_array_value(unsigned int array_size,
354				      struct gpio_desc **desc_array,
355				      struct gpio_array *array_info,
356				      unsigned long *value_bitmap)
357	int gpiod_set_array_value_cansleep(unsigned int array_size,
358					   struct gpio_desc **desc_array,
359					   struct gpio_array *array_info,
360					   unsigned long *value_bitmap)
361	int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
362					       struct gpio_desc **desc_array,
363					       struct gpio_array *array_info,
364					       unsigned long *value_bitmap)
365
366The array can be an arbitrary set of GPIOs. The functions will try to access
367GPIOs belonging to the same bank or chip simultaneously if supported by the
368corresponding chip driver. In that case a significantly improved performance
369can be expected. If simultaneous access is not possible the GPIOs will be
370accessed sequentially.
371
372The functions take four arguments:
373
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)
379
380The descriptor array can be obtained using the gpiod_get_array() function
381or one of its variants. If the group of descriptors returned by that function
382matches the desired group of GPIOs, those GPIOs can be accessed by simply using
383the struct gpio_descs returned by gpiod_get_array()::
384
385	struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
386	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
387			      my_gpio_descs->info, my_gpio_value_bitmap);
388
389It is also possible to access a completely arbitrary array of descriptors. The
390descriptors may be obtained using any combination of gpiod_get() and
391gpiod_get_array(). Afterwards the array of descriptors has to be setup
392manually before it can be passed to one of the above functions.  In that case,
393array_info should be set to NULL.
394
395Note that for optimal performance GPIOs belonging to the same chip should be
396contiguous within the array of descriptors.
397
398Still better performance may be achieved if array indexes of the descriptors
399match hardware pin numbers of a single chip.  If an array passed to a get/set
400array function matches the one obtained from gpiod_get_array() and array_info
401associated with the array is also passed, the function may take a fast bitmap
402processing path, passing the value_bitmap argument directly to the respective
403.get/set_multiple() callback of the chip.  That allows for utilization of GPIO
404banks as data I/O ports without much loss of performance.
405
406The return value of gpiod_get_array_value() and its variants is 0 on success
407or negative on error. Note the difference to gpiod_get_value(), which returns
4080 or 1 on success to convey the GPIO value. With the array functions, the GPIO
409values are stored in value_array rather than passed back as return value.
410
411
412GPIOs mapped to IRQs
413--------------------
414GPIO lines can quite often be used as IRQs. You can get the IRQ number
415corresponding to a given GPIO using the following call::
416
417	int gpiod_to_irq(const struct gpio_desc *desc)
418
419It will return an IRQ number, or a negative errno code if the mapping can't be
420done (most likely because that particular GPIO cannot be used as IRQ). It is an
421unchecked error to use a GPIO that wasn't set up as an input using
422gpiod_direction_input(), or to use an IRQ number that didn't originally come
423from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
424
425Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
426free_irq(). They will often be stored into IRQ resources for platform devices,
427by the board-specific initialization code. Note that IRQ trigger options are
428part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
429capabilities.
430
431
432GPIOs and ACPI
433==============
434
435On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
436the _CRS configuration objects of devices.  Those resources do not provide
437connection IDs (names) for GPIOs, so it is necessary to use an additional
438mechanism for this purpose.
439
440Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
441which, among other things, may be used to provide connection IDs for specific
442GPIOs described by the GpioIo()/GpioInt() resources in _CRS.  If that is the
443case, 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
445connection IDs need to be provided by device drivers.
446
447For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
448
449
450Interacting With the Legacy GPIO Subsystem
451==========================================
452Many kernel subsystems and drivers still handle GPIOs using the legacy
453integer-based interface. It is strongly recommended to update these to the new
454gpiod interface. For cases where both interfaces need to be used, the following
455two functions allow to convert a GPIO descriptor into the GPIO integer namespace
456and vice-versa::
457
458	int desc_to_gpio(const struct gpio_desc *desc)
459	struct gpio_desc *gpio_to_desc(unsigned gpio)
460
461The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
462the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
463All the same, a GPIO number passed to gpio_to_desc() must first be properly
464acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
465considered valid until that GPIO number is released using gpio_free().
466
467Freeing a GPIO obtained by one API with the other API is forbidden and an
468unchecked error.
469