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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
42The flags parameter is used to optionally specify a direction and initial value
43for 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.
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090050
51Both functions return either a valid GPIO descriptor, or an error code checkable
Alexandre Courbot2a3cf6a2013-12-11 11:32:28 +090052with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
53if and only if no GPIO has been assigned to the device/function/index triplet,
54other error codes are used for cases where a GPIO has been assigned but an error
Carlos Garciac98be0c2014-04-04 22:31:00 -040055occurred while trying to acquire it. This is useful to discriminate between mere
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070056errors and an absence of GPIO for optional GPIO parameters. For the common
57pattern where a GPIO is optional, the gpiod_get_optional() and
58gpiod_get_index_optional() functions can be used. These functions return NULL
59instead of -ENOENT if no GPIO has been assigned to the requested function:
60
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -070061 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)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090069
Rojhalat Ibrahim66858522015-02-11 17:27:58 +010070For 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
76This function returns a struct gpio_descs which contains an array of
77descriptors:
78
79 struct gpio_descs {
80 unsigned int ndescs;
81 struct gpio_desc *desc[];
82 }
83
84The following function returns NULL instead of -ENOENT if no GPIOs have been
85assigned 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
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090091Device-managed variants of these functions are also defined:
92
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090093 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
94 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +090095
96 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
97 const char *con_id,
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +090098 unsigned int idx,
99 enum gpiod_flags flags)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900100
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700101 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
102 const char *con_id,
103 enum gpiod_flags flags)
104
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100105 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
Alexandre Courbot1b11a9b2014-08-18 09:39:01 -0700106 const char *con_id,
107 unsigned int index,
108 enum gpiod_flags flags)
109
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100110 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
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900118A GPIO descriptor can be disposed of using the gpiod_put() function:
119
120 void gpiod_put(struct gpio_desc *desc)
121
Rojhalat Ibrahim66858522015-02-11 17:27:58 +0100122For an array of GPIOs this function can be used:
123
124 void gpiod_put_array(struct gpio_descs *descs)
125
126It is strictly forbidden to use a descriptor after calling these functions.
127It is also not allowed to individually release descriptors (using gpiod_put())
128from an array acquired with gpiod_get_array().
129
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100130The device-managed variants are, unsurprisingly:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900131
132 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
133
Rojhalat Ibrahim331758e2015-02-11 17:28:02 +0100134 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
135
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900136
137Using GPIOs
138===========
139
140Setting Direction
141-----------------
Alexandre Courbot39b2bbe2014-07-25 23:38:36 +0900142The first thing a driver must do with a GPIO is setting its direction. If no
143direction-setting flags have been given to gpiod_get*(), this is done by
144invoking one of the gpiod_direction_*() functions:
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900145
146 int gpiod_direction_input(struct gpio_desc *desc)
147 int gpiod_direction_output(struct gpio_desc *desc, int value)
148
149The return value is zero for success, else a negative errno. It should be
150checked, since the get/set calls don't return errors and since misconfiguration
151is possible. You should normally issue these calls from a task context. However,
152for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
153of early board setup.
154
155For output GPIOs, the value provided becomes the initial output value. This
156helps avoid signal glitching during system startup.
157
158A driver can also query the current direction of a GPIO:
159
160 int gpiod_get_direction(const struct gpio_desc *desc)
161
162This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT.
163
164Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
165without setting its direction first is illegal and will result in undefined
166behavior!**
167
168
169Spinlock-Safe GPIO Access
170-------------------------
171Most GPIO controllers can be accessed with memory read/write instructions. Those
172don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
173handlers and similar contexts.
174
175Use 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
180The values are boolean, zero for low, nonzero for high. When reading the value
181of an output pin, the value returned should be what's seen on the pin. That
182won't always match the specified output value, because of issues including
183open-drain signaling and output latencies.
184
185The get/set calls do not return errors because "invalid GPIO" should have been
186reported earlier from gpiod_direction_*(). However, note that not all platforms
187can read the value of output pins; those that can't should always return zero.
188Also, using these calls for GPIOs that can't safely be accessed without sleeping
189(see below) is an error.
190
191
192GPIO Access That May Sleep
193--------------------------
194Some GPIO controllers must be accessed using message based buses like I2C or
195SPI. Commands to read or write those GPIO values require waiting to get to the
196head of a queue to transmit a command and get its response. This requires
197sleeping, which can't be done from inside IRQ handlers.
198
199Platforms that support this type of GPIO distinguish them from other GPIOs by
200returning nonzero from this call:
201
202 int gpiod_cansleep(const struct gpio_desc *desc)
203
204To 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
209Accessing such GPIOs requires a context which may sleep, for example a threaded
210IRQ handler, and those accessors must be used instead of spinlock-safe
211accessors without the cansleep() name suffix.
212
213Other than the fact that these accessors might sleep, and will work on GPIOs
214that can't be accessed from hardIRQ handlers, these calls act the same as the
215spinlock-safe calls.
216
217
218Active-low State and Raw GPIO Values
219------------------------------------
220Device drivers like to manage the logical state of a GPIO, i.e. the value their
221device will actually receive, no matter what lies between it and the GPIO line.
222In some cases, it might make sense to control the actual GPIO line value. The
223following set of calls ignore the active-low property of a GPIO and work on the
224raw 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)
Philipp Zabelef70bbe2014-01-07 12:34:11 +0100230 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900231
232The 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
236Note that these functions should only be used with great moderation ; a driver
237should not have to care about the physical line level.
238
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100239
240Set multiple GPIO outputs with a single function call
241-----------------------------------------------------
242The following functions set the output values of an array of GPIOs:
243
244 void gpiod_set_array(unsigned int array_size,
245 struct gpio_desc **desc_array,
246 int *value_array)
247 void gpiod_set_raw_array(unsigned int array_size,
248 struct gpio_desc **desc_array,
249 int *value_array)
250 void gpiod_set_array_cansleep(unsigned int array_size,
251 struct gpio_desc **desc_array,
252 int *value_array)
253 void gpiod_set_raw_array_cansleep(unsigned int array_size,
254 struct gpio_desc **desc_array,
255 int *value_array)
256
257The array can be an arbitrary set of GPIOs. The functions will try to set
258GPIOs belonging to the same bank or chip simultaneously if supported by the
259corresponding chip driver. In that case a significantly improved performance
260can be expected. If simultaneous setting is not possible the GPIOs will be set
261sequentially.
Rojhalat Ibrahimde3b6962015-03-05 14:36:36 +0100262
263The 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
268The descriptor array can be obtained using the gpiod_get_array() function
269or one of its variants. If the group of descriptors returned by that function
270matches the desired group of GPIOs, those GPIOs can be set by simply using
271the struct gpio_descs returned by gpiod_get_array():
272
273 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
274 gpiod_set_array(my_gpio_descs->ndescs, my_gpio_descs->desc,
275 my_gpio_values);
276
277It is also possible to set a completely arbitrary array of descriptors. The
278descriptors may be obtained using any combination of gpiod_get() and
279gpiod_get_array(). Afterwards the array of descriptors has to be setup
280manually before it can be used with gpiod_set_array().
281
Rojhalat Ibrahim5f424242014-11-04 17:12:06 +0100282Note that for optimal performance GPIOs belonging to the same chip should be
283contiguous within the array of descriptors.
284
285
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900286GPIOs mapped to IRQs
287--------------------
288GPIO lines can quite often be used as IRQs. You can get the IRQ number
289corresponding to a given GPIO using the following call:
290
291 int gpiod_to_irq(const struct gpio_desc *desc)
292
293It will return an IRQ number, or an negative errno code if the mapping can't be
294done (most likely because that particular GPIO cannot be used as IRQ). It is an
295unchecked error to use a GPIO that wasn't set up as an input using
296gpiod_direction_input(), or to use an IRQ number that didn't originally come
297from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
298
299Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
300free_irq(). They will often be stored into IRQ resources for platform devices,
301by the board-specific initialization code. Note that IRQ trigger options are
302part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
303capabilities.
304
305
Rafael J. Wysockie36d4532014-11-03 23:39:57 +0100306GPIOs and ACPI
307==============
308
309On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
310the _CRS configuration objects of devices. Those resources do not provide
311connection IDs (names) for GPIOs, so it is necessary to use an additional
312mechanism for this purpose.
313
314Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
315which, among other things, may be used to provide connection IDs for specific
316GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
317case, 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
319connection IDs need to be provided by device drivers.
320
321For details refer to Documentation/acpi/gpio-properties.txt
322
323
Alexandre Courbotfd8e1982013-11-16 21:34:21 +0900324Interacting With the Legacy GPIO Subsystem
325==========================================
326Many kernel subsystems still handle GPIOs using the legacy integer-based
327interface. Although it is strongly encouraged to upgrade them to the safer
328descriptor-based API, the following two functions allow you to convert a GPIO
329descriptor 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
334The GPIO number returned by desc_to_gpio() can be safely used as long as the
335GPIO descriptor has not been freed. All the same, a GPIO number passed to
336gpio_to_desc() must have been properly acquired, and usage of the returned GPIO
337descriptor is only possible after the GPIO number has been released.
338
339Freeing a GPIO obtained by one API with the other API is forbidden and an
340unchecked error.