[deliverable/linux.git] / Documentation / gpio / consumer.txt

GPIO Descriptor Consumer Interface
==================================

This document describes the consumer interface of the GPIO framework. Note that
it describes the new descriptor-based interface. For a description of the
deprecated integer-based GPIO interface please refer to gpio-legacy.txt.


Guidelines for GPIOs consumers
==============================

Drivers that can't work without standard GPIO calls should have Kconfig entries
that depend on GPIOLIB. The functions that allow a driver to obtain and use
GPIOs are available by including the following file:

	#include <linux/gpio/consumer.h>

All the functions that work with the descriptor-based GPIO interface are
prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
other function in the kernel should use these prefixes.


Obtaining and Disposing GPIOs
=============================

With the descriptor-based interface, GPIOs are identified with an opaque,
non-forgeable handler that must be obtained through a call to one of the
gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
device that will use the GPIO and the function the requested GPIO is supposed to
fulfill:

	struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
				    enum gpiod_flags flags)

If a function is implemented by using several GPIOs together (e.g. a simple LED
device that displays digits), an additional index argument can be specified:

	struct gpio_desc *gpiod_get_index(struct device *dev,
					  const char *con_id, unsigned int idx,
					  enum gpiod_flags flags)

The flags parameter is used to optionally specify a direction and initial value
for the GPIO. Values can be:

* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
  later with one of the dedicated functions.
* GPIOD_IN to initialize the GPIO as input.
* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.

Both functions return either a valid GPIO descriptor, or an error code checkable
with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
if and only if no GPIO has been assigned to the device/function/index triplet,
other error codes are used for cases where a GPIO has been assigned but an error
occurred while trying to acquire it. This is useful to discriminate between mere
errors and an absence of GPIO for optional GPIO parameters. For the common
pattern where a GPIO is optional, the gpiod_get_optional() and
gpiod_get_index_optional() functions can be used. These functions return NULL
instead of -ENOENT if no GPIO has been assigned to the requested function:

	struct gpio_desc *gpiod_get_optional(struct device *dev,
					     const char *con_id,
					     enum gpiod_flags flags)

	struct gpio_desc *gpiod_get_index_optional(struct device *dev,
						   const char *con_id,
						   unsigned int index,
						   enum gpiod_flags flags)

For a function using multiple GPIOs all of those can be obtained with one call:

	struct gpio_descs *gpiod_get_array(struct device *dev,
					   const char *con_id,
					   enum gpiod_flags flags)

This function returns a struct gpio_descs which contains an array of
descriptors:

	struct gpio_descs {
		unsigned int ndescs;
		struct gpio_desc *desc[];
	}

The following function returns NULL instead of -ENOENT if no GPIOs have been
assigned to the requested function:

	struct gpio_descs *gpiod_get_array_optional(struct device *dev,
						    const char *con_id,
						    enum gpiod_flags flags)

Device-managed variants of these functions are also defined:

	struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
					 enum gpiod_flags flags)

	struct gpio_desc *devm_gpiod_get_index(struct device *dev,
					       const char *con_id,
					       unsigned int idx,
					       enum gpiod_flags flags)

	struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
						  const char *con_id,
						  enum gpiod_flags flags)

	struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
							const char *con_id,
							unsigned int index,
							enum gpiod_flags flags)

	struct gpio_descs *devm_gpiod_get_array(struct device *dev,
						const char *con_id,
						enum gpiod_flags flags)

	struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
							 const char *con_id,
							 enum gpiod_flags flags)

A GPIO descriptor can be disposed of using the gpiod_put() function:

	void gpiod_put(struct gpio_desc *desc)

For an array of GPIOs this function can be used:

	void gpiod_put_array(struct gpio_descs *descs)

It is strictly forbidden to use a descriptor after calling these functions.
It is also not allowed to individually release descriptors (using gpiod_put())
from an array acquired with gpiod_get_array().

The device-managed variants are, unsurprisingly:

	void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)

	void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)


Using GPIOs
===========

Setting Direction
-----------------
The first thing a driver must do with a GPIO is setting its direction. If no
direction-setting flags have been given to gpiod_get*(), this is done by
invoking one of the gpiod_direction_*() functions:

	int gpiod_direction_input(struct gpio_desc *desc)
	int gpiod_direction_output(struct gpio_desc *desc, int value)

The return value is zero for success, else a negative errno. It should be
checked, since the get/set calls don't return errors and since misconfiguration
is possible. You should normally issue these calls from a task context. However,
for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
of early board setup.

For output GPIOs, the value provided becomes the initial output value. This
helps avoid signal glitching during system startup.

A driver can also query the current direction of a GPIO:

	int gpiod_get_direction(const struct gpio_desc *desc)

This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.

Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
without setting its direction first is illegal and will result in undefined
behavior!**


Spinlock-Safe GPIO Access
-------------------------
Most GPIO controllers can be accessed with memory read/write instructions. Those
don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
handlers and similar contexts.

Use the following calls to access GPIOs from an atomic context:

	int gpiod_get_value(const struct gpio_desc *desc);
	void gpiod_set_value(struct gpio_desc *desc, int value);

The values are boolean, zero for low, nonzero for high. When reading the value
of an output pin, the value returned should be what's seen on the pin. That
won't always match the specified output value, because of issues including
open-drain signaling and output latencies.

The get/set calls do not return errors because "invalid GPIO" should have been
reported earlier from gpiod_direction_*(). However, note that not all platforms
can read the value of output pins; those that can't should always return zero.
Also, using these calls for GPIOs that can't safely be accessed without sleeping
(see below) is an error.


GPIO Access That May Sleep
--------------------------
Some GPIO controllers must be accessed using message based buses like I2C or
SPI. Commands to read or write those GPIO values require waiting to get to the
head of a queue to transmit a command and get its response. This requires
sleeping, which can't be done from inside IRQ handlers.

Platforms that support this type of GPIO distinguish them from other GPIOs by
returning nonzero from this call:

	int gpiod_cansleep(const struct gpio_desc *desc)

To access such GPIOs, a different set of accessors is defined:

	int gpiod_get_value_cansleep(const struct gpio_desc *desc)
	void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)

Accessing such GPIOs requires a context which may sleep, for example a threaded
IRQ handler, and those accessors must be used instead of spinlock-safe
accessors without the cansleep() name suffix.

Other than the fact that these accessors might sleep, and will work on GPIOs
that can't be accessed from hardIRQ handlers, these calls act the same as the
spinlock-safe calls.


Active-low State and Raw GPIO Values
------------------------------------
Device drivers like to manage the logical state of a GPIO, i.e. the value their
device will actually receive, no matter what lies between it and the GPIO line.
In some cases, it might make sense to control the actual GPIO line value. The
following set of calls ignore the active-low property of a GPIO and work on the
raw line value:

	int gpiod_get_raw_value(const struct gpio_desc *desc)
	void gpiod_set_raw_value(struct gpio_desc *desc, int value)
	int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
	void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
	int gpiod_direction_output_raw(struct gpio_desc *desc, int value)

The active-low state of a GPIO can also be queried using the following call:

	int gpiod_is_active_low(const struct gpio_desc *desc)

Note that these functions should only be used with great moderation ; a driver
should not have to care about the physical line level.


Set multiple GPIO outputs with a single function call
-----------------------------------------------------
The following functions set the output values of an array of GPIOs:

	void gpiod_set_array_value(unsigned int array_size,
				   struct gpio_desc **desc_array,
				   int *value_array)
	void gpiod_set_raw_array_value(unsigned int array_size,
				       struct gpio_desc **desc_array,
				       int *value_array)
	void gpiod_set_array_value_cansleep(unsigned int array_size,
					    struct gpio_desc **desc_array,
					    int *value_array)
	void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
						struct gpio_desc **desc_array,
						int *value_array)

The array can be an arbitrary set of GPIOs. The functions will try to set
GPIOs belonging to the same bank or chip simultaneously if supported by the
corresponding chip driver. In that case a significantly improved performance
can be expected. If simultaneous setting is not possible the GPIOs will be set
sequentially.

The gpiod_set_array() functions take three arguments:
	* array_size	- the number of array elements
	* desc_array	- an array of GPIO descriptors
	* value_array	- an array of values to assign to the GPIOs

The descriptor array can be obtained using the gpiod_get_array() function
or one of its variants. If the group of descriptors returned by that function
matches the desired group of GPIOs, those GPIOs can be set by simply using
the struct gpio_descs returned by gpiod_get_array():

	struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
			      my_gpio_values);

It is also possible to set a completely arbitrary array of descriptors. The
descriptors may be obtained using any combination of gpiod_get() and
gpiod_get_array(). Afterwards the array of descriptors has to be setup
manually before it can be used with gpiod_set_array().

Note that for optimal performance GPIOs belonging to the same chip should be
contiguous within the array of descriptors.


GPIOs mapped to IRQs
--------------------
GPIO lines can quite often be used as IRQs. You can get the IRQ number
corresponding to a given GPIO using the following call:

	int gpiod_to_irq(const struct gpio_desc *desc)

It will return an IRQ number, or a negative errno code if the mapping can't be
done (most likely because that particular GPIO cannot be used as IRQ). It is an
unchecked error to use a GPIO that wasn't set up as an input using
gpiod_direction_input(), or to use an IRQ number that didn't originally come
from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.

Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
free_irq(). They will often be stored into IRQ resources for platform devices,
by the board-specific initialization code. Note that IRQ trigger options are
part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
capabilities.


GPIOs and ACPI
==============

On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
the _CRS configuration objects of devices.  Those resources do not provide
connection IDs (names) for GPIOs, so it is necessary to use an additional
mechanism for this purpose.

Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
which, among other things, may be used to provide connection IDs for specific
GPIOs described by the GpioIo()/GpioInt() resources in _CRS.  If that is the
case, it will be handled by the GPIO subsystem automatically.  However, if the
_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
connection IDs need to be provided by device drivers.

For details refer to Documentation/acpi/gpio-properties.txt


Interacting With the Legacy GPIO Subsystem
==========================================
Many kernel subsystems still handle GPIOs using the legacy integer-based
interface. Although it is strongly encouraged to upgrade them to the safer
descriptor-based API, the following two functions allow you to convert a GPIO
descriptor into the GPIO integer namespace and vice-versa:

	int desc_to_gpio(const struct gpio_desc *desc)
	struct gpio_desc *gpio_to_desc(unsigned gpio)

The GPIO number returned by desc_to_gpio() can be safely used as long as the
GPIO descriptor has not been freed. All the same, a GPIO number passed to
gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
descriptor is only possible after the GPIO number has been released.

Freeing a GPIO obtained by one API with the other API is forbidden and an
unchecked error.
Commit	Line	Data
fd8e198c AC	1	GPIO Descriptor Consumer Interface
	2	==================================
	3
	4	This document describes the consumer interface of the GPIO framework. Note that
	5	it describes the new descriptor-based interface. For a description of the
	6	deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
	7
	8
	9	Guidelines for GPIOs consumers
	10	==============================
	11
	12	Drivers that can't work without standard GPIO calls should have Kconfig entries
	13	that depend on GPIOLIB. The functions that allow a driver to obtain and use
	14	GPIOs are available by including the following file:
	15
	16	#include <linux/gpio/consumer.h>
	17
	18	All the functions that work with the descriptor-based GPIO interface are
	19	prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
	20	other function in the kernel should use these prefixes.
	21
	22
	23	Obtaining and Disposing GPIOs
	24	=============================
	25
	26	With the descriptor-based interface, GPIOs are identified with an opaque,
	27	non-forgeable handler that must be obtained through a call to one of the
	28	gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
	29	device that will use the GPIO and the function the requested GPIO is supposed to
	30	fulfill:
	31
39b2bbe3 AC	32	struct gpio_desc gpiod_get(struct device dev, const char *con_id,
39b2bbe3 AC	33	enum gpiod_flags flags)
fd8e198c AC	34
	35	If a function is implemented by using several GPIOs together (e.g. a simple LED
	36	device that displays digits), an additional index argument can be specified:
	37
	38	struct gpio_desc gpiod_get_index(struct device dev,
39b2bbe3 AC	39	const char *con_id, unsigned int idx,
	40	enum gpiod_flags flags)
	41
	42	The flags parameter is used to optionally specify a direction and initial value
	43	for the GPIO. Values can be:
	44
	45	* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
	46	later with one of the dedicated functions.
	47	* GPIOD_IN to initialize the GPIO as input.
	48	* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
	49	* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
fd8e198c AC	50
fd8e198c AC	51	Both functions return either a valid GPIO descriptor, or an error code checkable
2a3cf6a3 AC	52	with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
	53	if and only if no GPIO has been assigned to the device/function/index triplet,
	54	other error codes are used for cases where a GPIO has been assigned but an error
c98be0c9	55	occurred while trying to acquire it. This is useful to discriminate between mere
1b11a9b9 AC	56	errors and an absence of GPIO for optional GPIO parameters. For the common
	57	pattern where a GPIO is optional, the gpiod_get_optional() and
	58	gpiod_get_index_optional() functions can be used. These functions return NULL
	59	instead of -ENOENT if no GPIO has been assigned to the requested function:
	60
1b11a9b9 AC	61	struct gpio_desc gpiod_get_optional(struct device dev,
	62	const char *con_id,
	63	enum gpiod_flags flags)
	64
	65	struct gpio_desc gpiod_get_index_optional(struct device dev,
	66	const char *con_id,
	67	unsigned int index,
	68	enum gpiod_flags flags)
fd8e198c	69
66858527 RI	70	For a function using multiple GPIOs all of those can be obtained with one call:
	71
	72	struct gpio_descs gpiod_get_array(struct device dev,
	73	const char *con_id,
	74	enum gpiod_flags flags)
	75
	76	This function returns a struct gpio_descs which contains an array of
	77	descriptors:
	78
	79	struct gpio_descs {
	80	unsigned int ndescs;
	81	struct gpio_desc *desc[];
	82	}
	83
	84	The following function returns NULL instead of -ENOENT if no GPIOs have been
	85	assigned to the requested function:
	86
	87	struct gpio_descs gpiod_get_array_optional(struct device dev,
	88	const char *con_id,
	89	enum gpiod_flags flags)
	90
fd8e198c AC	91	Device-managed variants of these functions are also defined:
fd8e198c AC	92
39b2bbe3 AC	93	struct gpio_desc devm_gpiod_get(struct device dev, const char *con_id,
39b2bbe3 AC	94	enum gpiod_flags flags)
fd8e198c AC	95
	96	struct gpio_desc devm_gpiod_get_index(struct device dev,
	97	const char *con_id,
39b2bbe3 AC	98	unsigned int idx,
39b2bbe3 AC	99	enum gpiod_flags flags)
fd8e198c	100
1b11a9b9 AC	101	struct gpio_desc devm_gpiod_get_optional(struct device dev,
	102	const char *con_id,
	103	enum gpiod_flags flags)
	104
331758ee	105	struct gpio_desc devm_gpiod_get_index_optional(struct device dev,
1b11a9b9 AC	106	const char *con_id,
	107	unsigned int index,
	108	enum gpiod_flags flags)
	109
331758ee RI	110	struct gpio_descs devm_gpiod_get_array(struct device dev,
	111	const char *con_id,
	112	enum gpiod_flags flags)
	113
	114	struct gpio_descs devm_gpiod_get_array_optional(struct device dev,
	115	const char *con_id,
	116	enum gpiod_flags flags)
	117
fd8e198c AC	118	A GPIO descriptor can be disposed of using the gpiod_put() function:
	119
	120	void gpiod_put(struct gpio_desc *desc)
	121
66858527 RI	122	For an array of GPIOs this function can be used:
	123
	124	void gpiod_put_array(struct gpio_descs *descs)
	125
	126	It is strictly forbidden to use a descriptor after calling these functions.
	127	It is also not allowed to individually release descriptors (using gpiod_put())
	128	from an array acquired with gpiod_get_array().
	129
331758ee	130	The device-managed variants are, unsurprisingly:
fd8e198c AC	131
	132	void devm_gpiod_put(struct device dev, struct gpio_desc desc)
	133
331758ee RI	134	void devm_gpiod_put_array(struct device dev, struct gpio_descs descs)
331758ee RI	135
fd8e198c AC	136
	137	Using GPIOs
	138	===========
	139
	140	Setting Direction
	141	-----------------
39b2bbe3 AC	142	The first thing a driver must do with a GPIO is setting its direction. If no
	143	direction-setting flags have been given to gpiod_get*(), this is done by
	144	invoking one of the gpiod_direction_*() functions:
fd8e198c AC	145
	146	int gpiod_direction_input(struct gpio_desc *desc)
	147	int gpiod_direction_output(struct gpio_desc *desc, int value)
	148
	149	The return value is zero for success, else a negative errno. It should be
	150	checked, since the get/set calls don't return errors and since misconfiguration
	151	is possible. You should normally issue these calls from a task context. However,
	152	for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
	153	of early board setup.
	154
	155	For output GPIOs, the value provided becomes the initial output value. This
	156	helps avoid signal glitching during system startup.
	157
	158	A driver can also query the current direction of a GPIO:
	159
	160	int gpiod_get_direction(const struct gpio_desc *desc)
	161
	162	This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.
	163
	164	Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
	165	without setting its direction first is illegal and will result in undefined
	166	behavior!**
	167
	168
	169	Spinlock-Safe GPIO Access
	170	-------------------------
	171	Most GPIO controllers can be accessed with memory read/write instructions. Those
	172	don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
	173	handlers and similar contexts.
	174
	175	Use the following calls to access GPIOs from an atomic context:
	176
	177	int gpiod_get_value(const struct gpio_desc *desc);
	178	void gpiod_set_value(struct gpio_desc *desc, int value);
	179
	180	The values are boolean, zero for low, nonzero for high. When reading the value
	181	of an output pin, the value returned should be what's seen on the pin. That
	182	won't always match the specified output value, because of issues including
	183	open-drain signaling and output latencies.
	184
	185	The get/set calls do not return errors because "invalid GPIO" should have been
	186	reported earlier from gpiod_direction_*(). However, note that not all platforms
	187	can read the value of output pins; those that can't should always return zero.
	188	Also, using these calls for GPIOs that can't safely be accessed without sleeping
	189	(see below) is an error.
	190
	191
	192	GPIO Access That May Sleep
	193	--------------------------
	194	Some GPIO controllers must be accessed using message based buses like I2C or
	195	SPI. Commands to read or write those GPIO values require waiting to get to the
	196	head of a queue to transmit a command and get its response. This requires
	197	sleeping, which can't be done from inside IRQ handlers.
	198
	199	Platforms that support this type of GPIO distinguish them from other GPIOs by
	200	returning nonzero from this call:
	201
	202	int gpiod_cansleep(const struct gpio_desc *desc)
	203
	204	To access such GPIOs, a different set of accessors is defined:
	205
	206	int gpiod_get_value_cansleep(const struct gpio_desc *desc)
	207	void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
	208
209	Accessing such GPIOs requires a context which may sleep, for example a threaded
210	IRQ handler, and those accessors must be used instead of spinlock-safe
211	accessors without the cansleep() name suffix.
212
213	Other than the fact that these accessors might sleep, and will work on GPIOs
214	that can't be accessed from hardIRQ handlers, these calls act the same as the
215	spinlock-safe calls.
216
217
218	Active-low State and Raw GPIO Values
219	------------------------------------
220	Device drivers like to manage the logical state of a GPIO, i.e. the value their
221	device will actually receive, no matter what lies between it and the GPIO line.
222	In some cases, it might make sense to control the actual GPIO line value. The
223	following set of calls ignore the active-low property of a GPIO and work on the
224	raw line value:
225
226	int gpiod_get_raw_value(const struct gpio_desc *desc)
227	void gpiod_set_raw_value(struct gpio_desc *desc, int value)
228	int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
229	void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
ef70bbe1	230	int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
fd8e198c AC	231
	232	The active-low state of a GPIO can also be queried using the following call:
	233
	234	int gpiod_is_active_low(const struct gpio_desc *desc)
	235
	236	Note that these functions should only be used with great moderation ; a driver
	237	should not have to care about the physical line level.
	238
5f424243 RI	239
	240	Set multiple GPIO outputs with a single function call
	241	-----------------------------------------------------
	242	The following functions set the output values of an array of GPIOs:
	243
e2bfba41 RI	244	void gpiod_set_array_value(unsigned int array_size,
	245	struct gpio_desc **desc_array,
	246	int *value_array)
	247	void gpiod_set_raw_array_value(unsigned int array_size,
	248	struct gpio_desc **desc_array,
	249	int *value_array)
	250	void gpiod_set_array_value_cansleep(unsigned int array_size,
	251	struct gpio_desc **desc_array,
	252	int *value_array)
	253	void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
	254	struct gpio_desc **desc_array,
	255	int *value_array)
5f424243 RI	256
	257	The array can be an arbitrary set of GPIOs. The functions will try to set
	258	GPIOs belonging to the same bank or chip simultaneously if supported by the
	259	corresponding chip driver. In that case a significantly improved performance
	260	can be expected. If simultaneous setting is not possible the GPIOs will be set
	261	sequentially.
de3b6965 RI	262
	263	The gpiod_set_array() functions take three arguments:
	264	* array_size - the number of array elements
	265	* desc_array - an array of GPIO descriptors
	266	* value_array - an array of values to assign to the GPIOs
	267
	268	The descriptor array can be obtained using the gpiod_get_array() function
	269	or one of its variants. If the group of descriptors returned by that function
	270	matches the desired group of GPIOs, those GPIOs can be set by simply using
	271	the struct gpio_descs returned by gpiod_get_array():
	272
	273	struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
e2bfba41 RI	274	gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
e2bfba41 RI	275	my_gpio_values);
de3b6965 RI	276
	277	It is also possible to set a completely arbitrary array of descriptors. The
	278	descriptors may be obtained using any combination of gpiod_get() and
	279	gpiod_get_array(). Afterwards the array of descriptors has to be setup
	280	manually before it can be used with gpiod_set_array().
	281
5f424243 RI	282	Note that for optimal performance GPIOs belonging to the same chip should be
	283	contiguous within the array of descriptors.
	284
	285
fd8e198c AC	286	GPIOs mapped to IRQs
	287	--------------------
	288	GPIO lines can quite often be used as IRQs. You can get the IRQ number
	289	corresponding to a given GPIO using the following call:
	290
	291	int gpiod_to_irq(const struct gpio_desc *desc)
	292
cbfa2c52	293	It will return an IRQ number, or a negative errno code if the mapping can't be
fd8e198c AC	294	done (most likely because that particular GPIO cannot be used as IRQ). It is an
	295	unchecked error to use a GPIO that wasn't set up as an input using
	296	gpiod_direction_input(), or to use an IRQ number that didn't originally come
	297	from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
	298
	299	Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
	300	free_irq(). They will often be stored into IRQ resources for platform devices,
	301	by the board-specific initialization code. Note that IRQ trigger options are
	302	part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
	303	capabilities.
	304
	305
e36d453e RW	306	GPIOs and ACPI
	307	==============
	308
	309	On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
	310	the _CRS configuration objects of devices. Those resources do not provide
	311	connection IDs (names) for GPIOs, so it is necessary to use an additional
	312	mechanism for this purpose.
	313
	314	Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
	315	which, among other things, may be used to provide connection IDs for specific
	316	GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
	317	case, it will be handled by the GPIO subsystem automatically. However, if the
	318	_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
	319	connection IDs need to be provided by device drivers.
	320
	321	For details refer to Documentation/acpi/gpio-properties.txt
	322
	323
fd8e198c AC	324	Interacting With the Legacy GPIO Subsystem
	325	==========================================
	326	Many kernel subsystems still handle GPIOs using the legacy integer-based
	327	interface. Although it is strongly encouraged to upgrade them to the safer
	328	descriptor-based API, the following two functions allow you to convert a GPIO
	329	descriptor into the GPIO integer namespace and vice-versa:
	330
	331	int desc_to_gpio(const struct gpio_desc *desc)
	332	struct gpio_desc *gpio_to_desc(unsigned gpio)
	333
	334	The GPIO number returned by desc_to_gpio() can be safely used as long as the
	335	GPIO descriptor has not been freed. All the same, a GPIO number passed to
	336	gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
	337	descriptor is only possible after the GPIO number has been released.
	338
	339	Freeing a GPIO obtained by one API with the other API is forbidden and an
	340	unchecked error.