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
75The two last flags are used for use cases where open drain is mandatory, such
76as I2C: if the line is not already configured as open drain in the mappings
77(see board.txt), then open drain will be enforced anyway and a warning will be
78printed that the board configuration needs to be updated to match the use case.
79
80Both functions return either a valid GPIO descriptor, or an error code checkable
81with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
82if and only if no GPIO has been assigned to the device/function/index triplet,
83other error codes are used for cases where a GPIO has been assigned but an error
84occurred while trying to acquire it. This is useful to discriminate between mere
85errors and an absence of GPIO for optional GPIO parameters. For the common
86pattern where a GPIO is optional, the gpiod_get_optional() and
87gpiod_get_index_optional() functions can be used. These functions return NULL
88instead of -ENOENT if no GPIO has been assigned to the requested function::
89
90	struct gpio_desc *gpiod_get_optional(struct device *dev,
91					     const char *con_id,
92					     enum gpiod_flags flags)
93
94	struct gpio_desc *gpiod_get_index_optional(struct device *dev,
95						   const char *con_id,
96						   unsigned int index,
97						   enum gpiod_flags flags)
98
99Note that gpio_get*_optional() functions (and their managed variants), unlike
100the rest of gpiolib API, also return NULL when gpiolib support is disabled.
101This is helpful to driver authors, since they do not need to special case
102-ENOSYS return codes.  System integrators should however be careful to enable
103gpiolib on systems that need it.
104
105For a function using multiple GPIOs all of those can be obtained with one call::
106
107	struct gpio_descs *gpiod_get_array(struct device *dev,
108					   const char *con_id,
109					   enum gpiod_flags flags)
110
111This function returns a struct gpio_descs which contains an array of
112descriptors.  It also contains a pointer to a gpiolib private structure which,
113if passed back to get/set array functions, may speed up I/O proocessing::
114
115	struct gpio_descs {
116		struct gpio_array *info;
117		unsigned int ndescs;
118		struct gpio_desc *desc[];
119	}
120
121The following function returns NULL instead of -ENOENT if no GPIOs have been
122assigned to the requested function::
123
124	struct gpio_descs *gpiod_get_array_optional(struct device *dev,
125						    const char *con_id,
126						    enum gpiod_flags flags)
127
128Device-managed variants of these functions are also defined::
129
130	struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
131					 enum gpiod_flags flags)
132
133	struct gpio_desc *devm_gpiod_get_index(struct device *dev,
134					       const char *con_id,
135					       unsigned int idx,
136					       enum gpiod_flags flags)
137
138	struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
139						  const char *con_id,
140						  enum gpiod_flags flags)
141
142	struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
143							const char *con_id,
144							unsigned int index,
145							enum gpiod_flags flags)
146
147	struct gpio_descs *devm_gpiod_get_array(struct device *dev,
148						const char *con_id,
149						enum gpiod_flags flags)
150
151	struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
152							 const char *con_id,
153							 enum gpiod_flags flags)
154
155A GPIO descriptor can be disposed of using the gpiod_put() function::
156
157	void gpiod_put(struct gpio_desc *desc)
158
159For an array of GPIOs this function can be used::
160
161	void gpiod_put_array(struct gpio_descs *descs)
162
163It is strictly forbidden to use a descriptor after calling these functions.
164It is also not allowed to individually release descriptors (using gpiod_put())
165from an array acquired with gpiod_get_array().
166
167The device-managed variants are, unsurprisingly::
168
169	void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
170
171	void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
172
173
174Using GPIOs
175===========
176
177Setting Direction
178-----------------
179The first thing a driver must do with a GPIO is setting its direction. If no
180direction-setting flags have been given to gpiod_get*(), this is done by
181invoking one of the gpiod_direction_*() functions::
182
183	int gpiod_direction_input(struct gpio_desc *desc)
184	int gpiod_direction_output(struct gpio_desc *desc, int value)
185
186The return value is zero for success, else a negative errno. It should be
187checked, since the get/set calls don't return errors and since misconfiguration
188is possible. You should normally issue these calls from a task context. However,
189for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
190of early board setup.
191
192For output GPIOs, the value provided becomes the initial output value. This
193helps avoid signal glitching during system startup.
194
195A driver can also query the current direction of a GPIO::
196
197	int gpiod_get_direction(const struct gpio_desc *desc)
198
199This function returns 0 for output, 1 for input, or an error code in case of error.
200
201Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
202without setting its direction first is illegal and will result in undefined
203behavior!**
204
205
206Spinlock-Safe GPIO Access
207-------------------------
208Most GPIO controllers can be accessed with memory read/write instructions. Those
209don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
210handlers and similar contexts.
211
212Use the following calls to access GPIOs from an atomic context::
213
214	int gpiod_get_value(const struct gpio_desc *desc);
215	void gpiod_set_value(struct gpio_desc *desc, int value);
216
217The values are boolean, zero for low, nonzero for high. When reading the value
218of an output pin, the value returned should be what's seen on the pin. That
219won't always match the specified output value, because of issues including
220open-drain signaling and output latencies.
221
222The get/set calls do not return errors because "invalid GPIO" should have been
223reported earlier from gpiod_direction_*(). However, note that not all platforms
224can read the value of output pins; those that can't should always return zero.
225Also, using these calls for GPIOs that can't safely be accessed without sleeping
226(see below) is an error.
227
228
229GPIO Access That May Sleep
230--------------------------
231Some GPIO controllers must be accessed using message based buses like I2C or
232SPI. Commands to read or write those GPIO values require waiting to get to the
233head of a queue to transmit a command and get its response. This requires
234sleeping, which can't be done from inside IRQ handlers.
235
236Platforms that support this type of GPIO distinguish them from other GPIOs by
237returning nonzero from this call::
238
239	int gpiod_cansleep(const struct gpio_desc *desc)
240
241To access such GPIOs, a different set of accessors is defined::
242
243	int gpiod_get_value_cansleep(const struct gpio_desc *desc)
244	void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
245
246Accessing such GPIOs requires a context which may sleep, for example a threaded
247IRQ handler, and those accessors must be used instead of spinlock-safe
248accessors without the cansleep() name suffix.
249
250Other than the fact that these accessors might sleep, and will work on GPIOs
251that can't be accessed from hardIRQ handlers, these calls act the same as the
252spinlock-safe calls.
253
254
255The active low and open drain semantics
256---------------------------------------
257As a consumer should not have to care about the physical line level, all of the
258gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
259the *logical* value. With this they take the active low property into account.
260This means that they check whether the GPIO is configured to be active low,
261and if so, they manipulate the passed value before the physical line level is
262driven.
263
264The same is applicable for open drain or open source output lines: those do not
265actively drive their output high (open drain) or low (open source), they just
266switch their output to a high impedance value. The consumer should not need to
267care. (For details read about open drain in driver.txt.)
268
269With this, all the gpiod_set_(array)_value_xxx() functions interpret the
270parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
271level will be driven accordingly.
272
273As an example, if the active low property for a dedicated GPIO is set, and the
274gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
275will be driven low.
276
277To summarize::
278
279  Function (example)                 line property          physical line
280  gpiod_set_raw_value(desc, 0);      don't care             low
281  gpiod_set_raw_value(desc, 1);      don't care             high
282  gpiod_set_value(desc, 0);          default (active high)  low
283  gpiod_set_value(desc, 1);          default (active high)  high
284  gpiod_set_value(desc, 0);          active low             high
285  gpiod_set_value(desc, 1);          active low             low
286  gpiod_set_value(desc, 0);          default (active high)  low
287  gpiod_set_value(desc, 1);          default (active high)  high
288  gpiod_set_value(desc, 0);          open drain             low
289  gpiod_set_value(desc, 1);          open drain             high impedance
290  gpiod_set_value(desc, 0);          open source            high impedance
291  gpiod_set_value(desc, 1);          open source            high
292
293It is possible to override these semantics using the set_raw/get_raw functions
294but it should be avoided as much as possible, especially by system-agnostic drivers
295which should not need to care about the actual physical line level and worry about
296the logical value instead.
297
298
299Accessing raw GPIO values
300-------------------------
301Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
302their device will actually receive, no matter what lies between it and the GPIO
303line.
304
305The following set of calls ignore the active-low or open drain property of a GPIO and
306work on the raw line value::
307
308	int gpiod_get_raw_value(const struct gpio_desc *desc)
309	void gpiod_set_raw_value(struct gpio_desc *desc, int value)
310	int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
311	void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
312	int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
313
314The active low state of a GPIO can also be queried using the following call::
315
316	int gpiod_is_active_low(const struct gpio_desc *desc)
317
318Note that these functions should only be used with great moderation; a driver
319should not have to care about the physical line level or open drain semantics.
320
321
322Access multiple GPIOs with a single function call
323-------------------------------------------------
324The following functions get or set the values of an array of GPIOs::
325
326	int gpiod_get_array_value(unsigned int array_size,
327				  struct gpio_desc **desc_array,
328				  struct gpio_array *array_info,
329				  unsigned long *value_bitmap);
330	int gpiod_get_raw_array_value(unsigned int array_size,
331				      struct gpio_desc **desc_array,
332				      struct gpio_array *array_info,
333				      unsigned long *value_bitmap);
334	int gpiod_get_array_value_cansleep(unsigned int array_size,
335					   struct gpio_desc **desc_array,
336					   struct gpio_array *array_info,
337					   unsigned long *value_bitmap);
338	int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
339					   struct gpio_desc **desc_array,
340					   struct gpio_array *array_info,
341					   unsigned long *value_bitmap);
342
343	int gpiod_set_array_value(unsigned int array_size,
344				  struct gpio_desc **desc_array,
345				  struct gpio_array *array_info,
346				  unsigned long *value_bitmap)
347	int gpiod_set_raw_array_value(unsigned int array_size,
348				      struct gpio_desc **desc_array,
349				      struct gpio_array *array_info,
350				      unsigned long *value_bitmap)
351	int gpiod_set_array_value_cansleep(unsigned int array_size,
352					   struct gpio_desc **desc_array,
353					   struct gpio_array *array_info,
354					   unsigned long *value_bitmap)
355	int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
356					       struct gpio_desc **desc_array,
357					       struct gpio_array *array_info,
358					       unsigned long *value_bitmap)
359
360The array can be an arbitrary set of GPIOs. The functions will try to access
361GPIOs belonging to the same bank or chip simultaneously if supported by the
362corresponding chip driver. In that case a significantly improved performance
363can be expected. If simultaneous access is not possible the GPIOs will be
364accessed sequentially.
365
366The functions take three arguments:
367	* array_size	- the number of array elements
368	* desc_array	- an array of GPIO descriptors
369	* array_info	- optional information obtained from gpiod_array_get()
370	* value_bitmap	- a bitmap to store the GPIOs' values (get) or
371			  a bitmap of values to assign to the GPIOs (set)
372
373The descriptor array can be obtained using the gpiod_get_array() function
374or one of its variants. If the group of descriptors returned by that function
375matches the desired group of GPIOs, those GPIOs can be accessed by simply using
376the struct gpio_descs returned by gpiod_get_array()::
377
378	struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
379	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
380			      my_gpio_descs->info, my_gpio_value_bitmap);
381
382It is also possible to access a completely arbitrary array of descriptors. The
383descriptors may be obtained using any combination of gpiod_get() and
384gpiod_get_array(). Afterwards the array of descriptors has to be setup
385manually before it can be passed to one of the above functions.  In that case,
386array_info should be set to NULL.
387
388Note that for optimal performance GPIOs belonging to the same chip should be
389contiguous within the array of descriptors.
390
391Still better performance may be achieved if array indexes of the descriptors
392match hardware pin numbers of a single chip.  If an array passed to a get/set
393array function matches the one obtained from gpiod_get_array() and array_info
394associated with the array is also passed, the function may take a fast bitmap
395processing path, passing the value_bitmap argument directly to the respective
396.get/set_multiple() callback of the chip.  That allows for utilization of GPIO
397banks as data I/O ports without much loss of performance.
398
399The return value of gpiod_get_array_value() and its variants is 0 on success
400or negative on error. Note the difference to gpiod_get_value(), which returns
4010 or 1 on success to convey the GPIO value. With the array functions, the GPIO
402values are stored in value_array rather than passed back as return value.
403
404
405GPIOs mapped to IRQs
406--------------------
407GPIO lines can quite often be used as IRQs. You can get the IRQ number
408corresponding to a given GPIO using the following call::
409
410	int gpiod_to_irq(const struct gpio_desc *desc)
411
412It will return an IRQ number, or a negative errno code if the mapping can't be
413done (most likely because that particular GPIO cannot be used as IRQ). It is an
414unchecked error to use a GPIO that wasn't set up as an input using
415gpiod_direction_input(), or to use an IRQ number that didn't originally come
416from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
417
418Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
419free_irq(). They will often be stored into IRQ resources for platform devices,
420by the board-specific initialization code. Note that IRQ trigger options are
421part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
422capabilities.
423
424
425GPIOs and ACPI
426==============
427
428On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
429the _CRS configuration objects of devices.  Those resources do not provide
430connection IDs (names) for GPIOs, so it is necessary to use an additional
431mechanism for this purpose.
432
433Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
434which, among other things, may be used to provide connection IDs for specific
435GPIOs described by the GpioIo()/GpioInt() resources in _CRS.  If that is the
436case, it will be handled by the GPIO subsystem automatically.  However, if the
437_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
438connection IDs need to be provided by device drivers.
439
440For details refer to Documentation/acpi/gpio-properties.txt
441
442
443Interacting With the Legacy GPIO Subsystem
444==========================================
445Many kernel subsystems still handle GPIOs using the legacy integer-based
446interface. Although it is strongly encouraged to upgrade them to the safer
447descriptor-based API, the following two functions allow you to convert a GPIO
448descriptor into the GPIO integer namespace and vice-versa::
449
450	int desc_to_gpio(const struct gpio_desc *desc)
451	struct gpio_desc *gpio_to_desc(unsigned gpio)
452
453The GPIO number returned by desc_to_gpio() can be safely used as long as the
454GPIO descriptor has not been freed. All the same, a GPIO number passed to
455gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
456descriptor is only possible after the GPIO number has been released.
457
458Freeing a GPIO obtained by one API with the other API is forbidden and an
459unchecked error.
460