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Alexandre Courbotfd8e1982013-11-16 21:34:21 +09001GPIO Descriptor Consumer Interface
2==================================
3
4This document describes the consumer interface of the GPIO framework. Note that
5it describes the new descriptor-based interface. For a description of the
6deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
7
8
9Guidelines for GPIOs consumers
10==============================
11
12Drivers that can't work without standard GPIO calls should have Kconfig entries
13that depend on GPIOLIB. The functions that allow a driver to obtain and use
14GPIOs are available by including the following file:
15
16 #include <linux/gpio/consumer.h>
17
18All the functions that work with the descriptor-based GPIO interface are
19prefixed with gpiod_. The gpio_ prefix is used for the legacy interface. No
20other function in the kernel should use these prefixes.
21
22
23Obtaining and Disposing GPIOs
24=============================
25
26With the descriptor-based interface, GPIOs are identified with an opaque,
27non-forgeable handler that must be obtained through a call to one of the
28gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
29device that will use the GPIO and the function the requested GPIO is supposed to
30fulfill:
31
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090032 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
33 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090034
35If a function is implemented by using several GPIOs together (e.g. a simple LED
36device that displays digits), an additional index argument can be specified:
37
38 struct gpio_desc *gpiod_get_index(struct device *dev,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090039 const char *con_id, unsigned int idx,
40 enum gpiod_flags flags)
41
Dirk Behme87e77e42015-09-02 20:07:10 +020042For a more detailed description of the con_id parameter in the DeviceTree case
43see Documentation/gpio/board.txt
44
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090045The flags parameter is used to optionally specify a direction and initial value
46for the GPIO. Values can be:
47
48* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
49 later with one of the dedicated functions.
50* GPIOD_IN to initialize the GPIO as input.
51* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
52* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090053
54Both functions return either a valid GPIO descriptor, or an error code checkable
Alexandre Courbot2a3cf6a2013-12-11 11:32:28 +090055with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
56if and only if no GPIO has been assigned to the device/function/index triplet,
57other error codes are used for cases where a GPIO has been assigned but an error
Carlos Garciac98be0c2014-04-04 22:31:00 -040058occurred while trying to acquire it. This is useful to discriminate between mere
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070059errors and an absence of GPIO for optional GPIO parameters. For the common
60pattern where a GPIO is optional, the gpiod_get_optional() and
61gpiod_get_index_optional() functions can be used. These functions return NULL
62instead of -ENOENT if no GPIO has been assigned to the requested function:
63
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070064 struct gpio_desc *gpiod_get_optional(struct device *dev,
65 const char *con_id,
66 enum gpiod_flags flags)
67
68 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
69 const char *con_id,
70 unsigned int index,
71 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090072
Rojhalat Ibrahim66858522015-02-11 17:27:58 +010073For a function using multiple GPIOs all of those can be obtained with one call:
74
75 struct gpio_descs *gpiod_get_array(struct device *dev,
76 const char *con_id,
77 enum gpiod_flags flags)
78
79This function returns a struct gpio_descs which contains an array of
80descriptors:
81
82 struct gpio_descs {
83 unsigned int ndescs;
84 struct gpio_desc *desc[];
85 }
86
87The following function returns NULL instead of -ENOENT if no GPIOs have been
88assigned to the requested function:
89
90 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
91 const char *con_id,
92 enum gpiod_flags flags)
93
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090094Device-managed variants of these functions are also defined:
95
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090096 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
97 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090098
99 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
100 const char *con_id,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900101 unsigned int idx,
102 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900103
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700104 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
105 const char *con_id,
106 enum gpiod_flags flags)
107
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100108 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700109 const char *con_id,
110 unsigned int index,
111 enum gpiod_flags flags)
112
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100113 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
114 const char *con_id,
115 enum gpiod_flags flags)
116
117 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
118 const char *con_id,
119 enum gpiod_flags flags)
120
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900121A GPIO descriptor can be disposed of using the gpiod_put() function:
122
123 void gpiod_put(struct gpio_desc *desc)
124
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100125For an array of GPIOs this function can be used:
126
127 void gpiod_put_array(struct gpio_descs *descs)
128
129It is strictly forbidden to use a descriptor after calling these functions.
130It is also not allowed to individually release descriptors (using gpiod_put())
131from an array acquired with gpiod_get_array().
132
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100133The device-managed variants are, unsurprisingly:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900134
135 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
136
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100137 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
138
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900139
140Using GPIOs
141===========
142
143Setting Direction
144-----------------
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900145The first thing a driver must do with a GPIO is setting its direction. If no
146direction-setting flags have been given to gpiod_get*(), this is done by
147invoking one of the gpiod_direction_*() functions:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900148
149 int gpiod_direction_input(struct gpio_desc *desc)
150 int gpiod_direction_output(struct gpio_desc *desc, int value)
151
152The return value is zero for success, else a negative errno. It should be
153checked, since the get/set calls don't return errors and since misconfiguration
154is possible. You should normally issue these calls from a task context. However,
155for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
156of early board setup.
157
158For output GPIOs, the value provided becomes the initial output value. This
159helps avoid signal glitching during system startup.
160
161A driver can also query the current direction of a GPIO:
162
163 int gpiod_get_direction(const struct gpio_desc *desc)
164
165This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.
166
167Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
168without setting its direction first is illegal and will result in undefined
169behavior!**
170
171
172Spinlock-Safe GPIO Access
173-------------------------
174Most GPIO controllers can be accessed with memory read/write instructions. Those
175don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
176handlers and similar contexts.
177
178Use the following calls to access GPIOs from an atomic context:
179
180 int gpiod_get_value(const struct gpio_desc *desc);
181 void gpiod_set_value(struct gpio_desc *desc, int value);
182
183The values are boolean, zero for low, nonzero for high. When reading the value
184of an output pin, the value returned should be what's seen on the pin. That
185won't always match the specified output value, because of issues including
186open-drain signaling and output latencies.
187
188The get/set calls do not return errors because "invalid GPIO" should have been
189reported earlier from gpiod_direction_*(). However, note that not all platforms
190can read the value of output pins; those that can't should always return zero.
191Also, using these calls for GPIOs that can't safely be accessed without sleeping
192(see below) is an error.
193
194
195GPIO Access That May Sleep
196--------------------------
197Some GPIO controllers must be accessed using message based buses like I2C or
198SPI. Commands to read or write those GPIO values require waiting to get to the
199head of a queue to transmit a command and get its response. This requires
200sleeping, which can't be done from inside IRQ handlers.
201
202Platforms that support this type of GPIO distinguish them from other GPIOs by
203returning nonzero from this call:
204
205 int gpiod_cansleep(const struct gpio_desc *desc)
206
207To access such GPIOs, a different set of accessors is defined:
208
209 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
210 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
211
212Accessing such GPIOs requires a context which may sleep, for example a threaded
213IRQ handler, and those accessors must be used instead of spinlock-safe
214accessors without the cansleep() name suffix.
215
216Other than the fact that these accessors might sleep, and will work on GPIOs
217that can't be accessed from hardIRQ handlers, these calls act the same as the
218spinlock-safe calls.
219
220
221Active-low State and Raw GPIO Values
222------------------------------------
223Device drivers like to manage the logical state of a GPIO, i.e. the value their
224device will actually receive, no matter what lies between it and the GPIO line.
225In some cases, it might make sense to control the actual GPIO line value. The
226following set of calls ignore the active-low property of a GPIO and work on the
227raw line value:
228
229 int gpiod_get_raw_value(const struct gpio_desc *desc)
230 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
231 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
232 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
Philipp Zabelef70bbe2014-01-07 12:34:11 +0100233 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900234
235The active-low state of a GPIO can also be queried using the following call:
236
237 int gpiod_is_active_low(const struct gpio_desc *desc)
238
239Note that these functions should only be used with great moderation ; a driver
240should not have to care about the physical line level.
241
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100242
Dirk Behmeac49fbd2015-07-18 08:02:07 +0200243The active-low property
244-----------------------
245
246As a driver should not have to care about the physical line level, all of the
247gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
248the *logical* value. With this they take the active-low property into account.
249This means that they check whether the GPIO is configured to be active-low,
250and if so, they manipulate the passed value before the physical line level is
251driven.
252
253With this, all the gpiod_set_(array)_value_xxx() functions interpret the
254parameter "value" as "active" ("1") or "inactive" ("0"). The physical line
255level will be driven accordingly.
256
257As an example, if the active-low property for a dedicated GPIO is set, and the
258gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
259will be driven low.
260
261To summarize:
262
263Function (example) active-low proporty physical line
264gpiod_set_raw_value(desc, 0); don't care low
265gpiod_set_raw_value(desc, 1); don't care high
266gpiod_set_value(desc, 0); default (active-high) low
267gpiod_set_value(desc, 1); default (active-high) high
268gpiod_set_value(desc, 0); active-low high
269gpiod_set_value(desc, 1); active-low low
270
271Please note again that the set_raw/get_raw functions should be avoided as much
272as possible, especially by drivers which should not care about the actual
273physical line level and worry about the logical value instead.
274
275
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100276Set multiple GPIO outputs with a single function call
277-----------------------------------------------------
278The following functions set the output values of an array of GPIOs:
279
Rojhalat Ibrahime2bfba42015-06-02 11:38:06 +0200280 void gpiod_set_array_value(unsigned int array_size,
281 struct gpio_desc **desc_array,
282 int *value_array)
283 void gpiod_set_raw_array_value(unsigned int array_size,
284 struct gpio_desc **desc_array,
285 int *value_array)
286 void gpiod_set_array_value_cansleep(unsigned int array_size,
287 struct gpio_desc **desc_array,
288 int *value_array)
289 void gpiod_set_raw_array_value_cansleep(unsigned int array_size,
290 struct gpio_desc **desc_array,
291 int *value_array)
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100292
293The array can be an arbitrary set of GPIOs. The functions will try to set
294GPIOs belonging to the same bank or chip simultaneously if supported by the
295corresponding chip driver. In that case a significantly improved performance
296can be expected. If simultaneous setting is not possible the GPIOs will be set
297sequentially.
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100298
299The gpiod_set_array() functions take three arguments:
300 * array_size - the number of array elements
301 * desc_array - an array of GPIO descriptors
302 * value_array - an array of values to assign to the GPIOs
303
304The descriptor array can be obtained using the gpiod_get_array() function
305or one of its variants. If the group of descriptors returned by that function
306matches the desired group of GPIOs, those GPIOs can be set by simply using
307the struct gpio_descs returned by gpiod_get_array():
308
309 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
Rojhalat Ibrahime2bfba42015-06-02 11:38:06 +0200310 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
311 my_gpio_values);
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100312
313It is also possible to set a completely arbitrary array of descriptors. The
314descriptors may be obtained using any combination of gpiod_get() and
315gpiod_get_array(). Afterwards the array of descriptors has to be setup
316manually before it can be used with gpiod_set_array().
317
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100318Note that for optimal performance GPIOs belonging to the same chip should be
319contiguous within the array of descriptors.
320
321
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900322GPIOs mapped to IRQs
323--------------------
324GPIO lines can quite often be used as IRQs. You can get the IRQ number
325corresponding to a given GPIO using the following call:
326
327 int gpiod_to_irq(const struct gpio_desc *desc)
328
Geert Uytterhoevencbfa2c52015-05-21 14:07:50 +0200329It will return an IRQ number, or a negative errno code if the mapping can't be
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900330done (most likely because that particular GPIO cannot be used as IRQ). It is an
331unchecked error to use a GPIO that wasn't set up as an input using
332gpiod_direction_input(), or to use an IRQ number that didn't originally come
333from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
334
335Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
336free_irq(). They will often be stored into IRQ resources for platform devices,
337by the board-specific initialization code. Note that IRQ trigger options are
338part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
339capabilities.
340
341
Rafael J. Wysockie36d4532014-11-03 23:39:57 +0100342GPIOs and ACPI
343==============
344
345On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
346the _CRS configuration objects of devices. Those resources do not provide
347connection IDs (names) for GPIOs, so it is necessary to use an additional
348mechanism for this purpose.
349
350Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
351which, among other things, may be used to provide connection IDs for specific
352GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
353case, it will be handled by the GPIO subsystem automatically. However, if the
354_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
355connection IDs need to be provided by device drivers.
356
357For details refer to Documentation/acpi/gpio-properties.txt
358
359
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900360Interacting With the Legacy GPIO Subsystem
361==========================================
362Many kernel subsystems still handle GPIOs using the legacy integer-based
363interface. Although it is strongly encouraged to upgrade them to the safer
364descriptor-based API, the following two functions allow you to convert a GPIO
365descriptor into the GPIO integer namespace and vice-versa:
366
367 int desc_to_gpio(const struct gpio_desc *desc)
368 struct gpio_desc *gpio_to_desc(unsigned gpio)
369
370The GPIO number returned by desc_to_gpio() can be safely used as long as the
371GPIO descriptor has not been freed. All the same, a GPIO number passed to
372gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
373descriptor is only possible after the GPIO number has been released.
374
375Freeing a GPIO obtained by one API with the other API is forbidden and an
376unchecked error.