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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, |
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 | ||
87e77e46 DB |
42 | For a more detailed description of the con_id parameter in the DeviceTree case |
43 | see Documentation/gpio/board.txt | |
44 | ||
39b2bbe3 AC |
45 | The flags parameter is used to optionally specify a direction and initial value |
46 | for 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. | |
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53 | |
54 | Both functions return either a valid GPIO descriptor, or an error code checkable | |
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55 | with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned |
56 | if and only if no GPIO has been assigned to the device/function/index triplet, | |
57 | other error codes are used for cases where a GPIO has been assigned but an error | |
c98be0c9 | 58 | occurred while trying to acquire it. This is useful to discriminate between mere |
1b11a9b9 AC |
59 | errors and an absence of GPIO for optional GPIO parameters. For the common |
60 | pattern where a GPIO is optional, the gpiod_get_optional() and | |
61 | gpiod_get_index_optional() functions can be used. These functions return NULL | |
62 | instead of -ENOENT if no GPIO has been assigned to the requested function: | |
63 | ||
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64 | 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) | |
fd8e198c | 72 | |
66858527 RI |
73 | For 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 | ||
79 | This function returns a struct gpio_descs which contains an array of | |
80 | descriptors: | |
81 | ||
82 | struct gpio_descs { | |
83 | unsigned int ndescs; | |
84 | struct gpio_desc *desc[]; | |
85 | } | |
86 | ||
87 | The following function returns NULL instead of -ENOENT if no GPIOs have been | |
88 | assigned 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 | ||
fd8e198c AC |
94 | Device-managed variants of these functions are also defined: |
95 | ||
39b2bbe3 AC |
96 | struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, |
97 | enum gpiod_flags flags) | |
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98 | |
99 | struct gpio_desc *devm_gpiod_get_index(struct device *dev, | |
100 | const char *con_id, | |
39b2bbe3 AC |
101 | unsigned int idx, |
102 | enum gpiod_flags flags) | |
fd8e198c | 103 | |
1b11a9b9 AC |
104 | struct gpio_desc *devm_gpiod_get_optional(struct device *dev, |
105 | const char *con_id, | |
106 | enum gpiod_flags flags) | |
107 | ||
331758ee | 108 | struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, |
1b11a9b9 AC |
109 | const char *con_id, |
110 | unsigned int index, | |
111 | enum gpiod_flags flags) | |
112 | ||
331758ee RI |
113 | 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 | ||
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121 | A GPIO descriptor can be disposed of using the gpiod_put() function: |
122 | ||
123 | void gpiod_put(struct gpio_desc *desc) | |
124 | ||
66858527 RI |
125 | For an array of GPIOs this function can be used: |
126 | ||
127 | void gpiod_put_array(struct gpio_descs *descs) | |
128 | ||
129 | It is strictly forbidden to use a descriptor after calling these functions. | |
130 | It is also not allowed to individually release descriptors (using gpiod_put()) | |
131 | from an array acquired with gpiod_get_array(). | |
132 | ||
331758ee | 133 | The device-managed variants are, unsurprisingly: |
fd8e198c AC |
134 | |
135 | void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) | |
136 | ||
331758ee RI |
137 | void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) |
138 | ||
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139 | |
140 | Using GPIOs | |
141 | =========== | |
142 | ||
143 | Setting Direction | |
144 | ----------------- | |
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145 | The first thing a driver must do with a GPIO is setting its direction. If no |
146 | direction-setting flags have been given to gpiod_get*(), this is done by | |
147 | invoking one of the gpiod_direction_*() functions: | |
fd8e198c AC |
148 | |
149 | int gpiod_direction_input(struct gpio_desc *desc) | |
150 | int gpiod_direction_output(struct gpio_desc *desc, int value) | |
151 | ||
152 | The return value is zero for success, else a negative errno. It should be | |
153 | checked, since the get/set calls don't return errors and since misconfiguration | |
154 | is possible. You should normally issue these calls from a task context. However, | |
155 | for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part | |
156 | of early board setup. | |
157 | ||
158 | For output GPIOs, the value provided becomes the initial output value. This | |
159 | helps avoid signal glitching during system startup. | |
160 | ||
161 | A driver can also query the current direction of a GPIO: | |
162 | ||
163 | int gpiod_get_direction(const struct gpio_desc *desc) | |
164 | ||
165 | This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT. | |
166 | ||
167 | Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO | |
168 | without setting its direction first is illegal and will result in undefined | |
169 | behavior!** | |
170 | ||
171 | ||
172 | Spinlock-Safe GPIO Access | |
173 | ------------------------- | |
174 | Most GPIO controllers can be accessed with memory read/write instructions. Those | |
175 | don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ | |
176 | handlers and similar contexts. | |
177 | ||
178 | Use 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 | ||
183 | The values are boolean, zero for low, nonzero for high. When reading the value | |
184 | of an output pin, the value returned should be what's seen on the pin. That | |
185 | won't always match the specified output value, because of issues including | |
186 | open-drain signaling and output latencies. | |
187 | ||
188 | The get/set calls do not return errors because "invalid GPIO" should have been | |
189 | reported earlier from gpiod_direction_*(). However, note that not all platforms | |
190 | can read the value of output pins; those that can't should always return zero. | |
191 | Also, using these calls for GPIOs that can't safely be accessed without sleeping | |
192 | (see below) is an error. | |
193 | ||
194 | ||
195 | GPIO Access That May Sleep | |
196 | -------------------------- | |
197 | Some GPIO controllers must be accessed using message based buses like I2C or | |
198 | SPI. Commands to read or write those GPIO values require waiting to get to the | |
199 | head of a queue to transmit a command and get its response. This requires | |
200 | sleeping, which can't be done from inside IRQ handlers. | |
201 | ||
202 | Platforms that support this type of GPIO distinguish them from other GPIOs by | |
203 | returning nonzero from this call: | |
204 | ||
205 | int gpiod_cansleep(const struct gpio_desc *desc) | |
206 | ||
207 | To 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 | ||
212 | Accessing such GPIOs requires a context which may sleep, for example a threaded | |
213 | IRQ handler, and those accessors must be used instead of spinlock-safe | |
214 | accessors without the cansleep() name suffix. | |
215 | ||
216 | Other than the fact that these accessors might sleep, and will work on GPIOs | |
217 | that can't be accessed from hardIRQ handlers, these calls act the same as the | |
218 | spinlock-safe calls. | |
219 | ||
220 | ||
221 | Active-low State and Raw GPIO Values | |
222 | ------------------------------------ | |
223 | Device drivers like to manage the logical state of a GPIO, i.e. the value their | |
224 | device will actually receive, no matter what lies between it and the GPIO line. | |
225 | In some cases, it might make sense to control the actual GPIO line value. The | |
226 | following set of calls ignore the active-low property of a GPIO and work on the | |
227 | raw 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) | |
ef70bbe1 | 233 | int gpiod_direction_output_raw(struct gpio_desc *desc, int value) |
fd8e198c AC |
234 | |
235 | The 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 | ||
239 | Note that these functions should only be used with great moderation ; a driver | |
240 | should not have to care about the physical line level. | |
241 | ||
5f424243 | 242 | |
ac49fbd1 DB |
243 | The active-low property |
244 | ----------------------- | |
245 | ||
246 | As a driver should not have to care about the physical line level, all of the | |
247 | gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with | |
248 | the *logical* value. With this they take the active-low property into account. | |
249 | This means that they check whether the GPIO is configured to be active-low, | |
250 | and if so, they manipulate the passed value before the physical line level is | |
251 | driven. | |
252 | ||
253 | With this, all the gpiod_set_(array)_value_xxx() functions interpret the | |
254 | parameter "value" as "active" ("1") or "inactive" ("0"). The physical line | |
255 | level will be driven accordingly. | |
256 | ||
257 | As an example, if the active-low property for a dedicated GPIO is set, and the | |
258 | gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level | |
259 | will be driven low. | |
260 | ||
261 | To summarize: | |
262 | ||
547d4c10 | 263 | Function (example) active-low property physical line |
ac49fbd1 DB |
264 | gpiod_set_raw_value(desc, 0); don't care low |
265 | gpiod_set_raw_value(desc, 1); don't care high | |
266 | gpiod_set_value(desc, 0); default (active-high) low | |
267 | gpiod_set_value(desc, 1); default (active-high) high | |
268 | gpiod_set_value(desc, 0); active-low high | |
269 | gpiod_set_value(desc, 1); active-low low | |
270 | ||
271 | Please note again that the set_raw/get_raw functions should be avoided as much | |
272 | as possible, especially by drivers which should not care about the actual | |
273 | physical line level and worry about the logical value instead. | |
274 | ||
275 | ||
5f424243 RI |
276 | Set multiple GPIO outputs with a single function call |
277 | ----------------------------------------------------- | |
278 | The following functions set the output values of an array of GPIOs: | |
279 | ||
e2bfba41 RI |
280 | 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) | |
5f424243 RI |
292 | |
293 | The array can be an arbitrary set of GPIOs. The functions will try to set | |
294 | GPIOs belonging to the same bank or chip simultaneously if supported by the | |
295 | corresponding chip driver. In that case a significantly improved performance | |
296 | can be expected. If simultaneous setting is not possible the GPIOs will be set | |
297 | sequentially. | |
de3b6965 RI |
298 | |
299 | The 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 | ||
304 | The descriptor array can be obtained using the gpiod_get_array() function | |
305 | or one of its variants. If the group of descriptors returned by that function | |
306 | matches the desired group of GPIOs, those GPIOs can be set by simply using | |
307 | the struct gpio_descs returned by gpiod_get_array(): | |
308 | ||
309 | struct gpio_descs *my_gpio_descs = gpiod_get_array(...); | |
e2bfba41 RI |
310 | gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, |
311 | my_gpio_values); | |
de3b6965 RI |
312 | |
313 | It is also possible to set a completely arbitrary array of descriptors. The | |
314 | descriptors may be obtained using any combination of gpiod_get() and | |
315 | gpiod_get_array(). Afterwards the array of descriptors has to be setup | |
316 | manually before it can be used with gpiod_set_array(). | |
317 | ||
5f424243 RI |
318 | Note that for optimal performance GPIOs belonging to the same chip should be |
319 | contiguous within the array of descriptors. | |
320 | ||
321 | ||
fd8e198c AC |
322 | GPIOs mapped to IRQs |
323 | -------------------- | |
324 | GPIO lines can quite often be used as IRQs. You can get the IRQ number | |
325 | corresponding to a given GPIO using the following call: | |
326 | ||
327 | int gpiod_to_irq(const struct gpio_desc *desc) | |
328 | ||
cbfa2c52 | 329 | It will return an IRQ number, or a negative errno code if the mapping can't be |
fd8e198c AC |
330 | done (most likely because that particular GPIO cannot be used as IRQ). It is an |
331 | unchecked error to use a GPIO that wasn't set up as an input using | |
332 | gpiod_direction_input(), or to use an IRQ number that didn't originally come | |
333 | from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. | |
334 | ||
335 | Non-error values returned from gpiod_to_irq() can be passed to request_irq() or | |
336 | free_irq(). They will often be stored into IRQ resources for platform devices, | |
337 | by the board-specific initialization code. Note that IRQ trigger options are | |
338 | part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup | |
339 | capabilities. | |
340 | ||
341 | ||
e36d453e RW |
342 | GPIOs and ACPI |
343 | ============== | |
344 | ||
345 | On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by | |
346 | the _CRS configuration objects of devices. Those resources do not provide | |
347 | connection IDs (names) for GPIOs, so it is necessary to use an additional | |
348 | mechanism for this purpose. | |
349 | ||
350 | Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object | |
351 | which, among other things, may be used to provide connection IDs for specific | |
352 | GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the | |
353 | case, 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 | |
355 | connection IDs need to be provided by device drivers. | |
356 | ||
357 | For details refer to Documentation/acpi/gpio-properties.txt | |
358 | ||
359 | ||
fd8e198c AC |
360 | Interacting With the Legacy GPIO Subsystem |
361 | ========================================== | |
362 | Many kernel subsystems still handle GPIOs using the legacy integer-based | |
363 | interface. Although it is strongly encouraged to upgrade them to the safer | |
364 | descriptor-based API, the following two functions allow you to convert a GPIO | |
365 | descriptor 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 | ||
370 | The GPIO number returned by desc_to_gpio() can be safely used as long as the | |
371 | GPIO descriptor has not been freed. All the same, a GPIO number passed to | |
372 | gpio_to_desc() must have been properly acquired, and usage of the returned GPIO | |
373 | descriptor is only possible after the GPIO number has been released. | |
374 | ||
375 | Freeing a GPIO obtained by one API with the other API is forbidden and an | |
376 | unchecked error. |