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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 | |
22c40367 DT |
73 | Note that gpio_get*_optional() functions (and their managed variants), unlike |
74 | the rest of gpiolib API, also return NULL when gpiolib support is disabled. | |
75 | This is helpful to driver authors, since they do not need to special case | |
76 | -ENOSYS return codes. System integrators should however be careful to enable | |
77 | gpiolib on systems that need it. | |
78 | ||
66858527 RI |
79 | For a function using multiple GPIOs all of those can be obtained with one call: |
80 | ||
81 | struct gpio_descs *gpiod_get_array(struct device *dev, | |
82 | const char *con_id, | |
83 | enum gpiod_flags flags) | |
84 | ||
85 | This function returns a struct gpio_descs which contains an array of | |
86 | descriptors: | |
87 | ||
88 | struct gpio_descs { | |
89 | unsigned int ndescs; | |
90 | struct gpio_desc *desc[]; | |
91 | } | |
92 | ||
93 | The following function returns NULL instead of -ENOENT if no GPIOs have been | |
94 | assigned to the requested function: | |
95 | ||
96 | struct gpio_descs *gpiod_get_array_optional(struct device *dev, | |
97 | const char *con_id, | |
98 | enum gpiod_flags flags) | |
99 | ||
fd8e198c AC |
100 | Device-managed variants of these functions are also defined: |
101 | ||
39b2bbe3 AC |
102 | struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, |
103 | enum gpiod_flags flags) | |
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104 | |
105 | struct gpio_desc *devm_gpiod_get_index(struct device *dev, | |
106 | const char *con_id, | |
39b2bbe3 AC |
107 | unsigned int idx, |
108 | enum gpiod_flags flags) | |
fd8e198c | 109 | |
1b11a9b9 AC |
110 | struct gpio_desc *devm_gpiod_get_optional(struct device *dev, |
111 | const char *con_id, | |
112 | enum gpiod_flags flags) | |
113 | ||
331758ee | 114 | struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, |
1b11a9b9 AC |
115 | const char *con_id, |
116 | unsigned int index, | |
117 | enum gpiod_flags flags) | |
118 | ||
331758ee RI |
119 | struct gpio_descs *devm_gpiod_get_array(struct device *dev, |
120 | const char *con_id, | |
121 | enum gpiod_flags flags) | |
122 | ||
123 | struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev, | |
124 | const char *con_id, | |
125 | enum gpiod_flags flags) | |
126 | ||
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127 | A GPIO descriptor can be disposed of using the gpiod_put() function: |
128 | ||
129 | void gpiod_put(struct gpio_desc *desc) | |
130 | ||
66858527 RI |
131 | For an array of GPIOs this function can be used: |
132 | ||
133 | void gpiod_put_array(struct gpio_descs *descs) | |
134 | ||
135 | It is strictly forbidden to use a descriptor after calling these functions. | |
136 | It is also not allowed to individually release descriptors (using gpiod_put()) | |
137 | from an array acquired with gpiod_get_array(). | |
138 | ||
331758ee | 139 | The device-managed variants are, unsurprisingly: |
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140 | |
141 | void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) | |
142 | ||
331758ee RI |
143 | void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) |
144 | ||
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145 | |
146 | Using GPIOs | |
147 | =========== | |
148 | ||
149 | Setting Direction | |
150 | ----------------- | |
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151 | The first thing a driver must do with a GPIO is setting its direction. If no |
152 | direction-setting flags have been given to gpiod_get*(), this is done by | |
153 | invoking one of the gpiod_direction_*() functions: | |
fd8e198c AC |
154 | |
155 | int gpiod_direction_input(struct gpio_desc *desc) | |
156 | int gpiod_direction_output(struct gpio_desc *desc, int value) | |
157 | ||
158 | The return value is zero for success, else a negative errno. It should be | |
159 | checked, since the get/set calls don't return errors and since misconfiguration | |
160 | is possible. You should normally issue these calls from a task context. However, | |
161 | for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part | |
162 | of early board setup. | |
163 | ||
164 | For output GPIOs, the value provided becomes the initial output value. This | |
165 | helps avoid signal glitching during system startup. | |
166 | ||
167 | A driver can also query the current direction of a GPIO: | |
168 | ||
169 | int gpiod_get_direction(const struct gpio_desc *desc) | |
170 | ||
171 | This function will return either GPIOF_DIR_IN or GPIOF_DIR_OUT. | |
172 | ||
173 | Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO | |
174 | without setting its direction first is illegal and will result in undefined | |
175 | behavior!** | |
176 | ||
177 | ||
178 | Spinlock-Safe GPIO Access | |
179 | ------------------------- | |
180 | Most GPIO controllers can be accessed with memory read/write instructions. Those | |
181 | don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ | |
182 | handlers and similar contexts. | |
183 | ||
184 | Use the following calls to access GPIOs from an atomic context: | |
185 | ||
186 | int gpiod_get_value(const struct gpio_desc *desc); | |
187 | void gpiod_set_value(struct gpio_desc *desc, int value); | |
188 | ||
189 | The values are boolean, zero for low, nonzero for high. When reading the value | |
190 | of an output pin, the value returned should be what's seen on the pin. That | |
191 | won't always match the specified output value, because of issues including | |
192 | open-drain signaling and output latencies. | |
193 | ||
194 | The get/set calls do not return errors because "invalid GPIO" should have been | |
195 | reported earlier from gpiod_direction_*(). However, note that not all platforms | |
196 | can read the value of output pins; those that can't should always return zero. | |
197 | Also, using these calls for GPIOs that can't safely be accessed without sleeping | |
198 | (see below) is an error. | |
199 | ||
200 | ||
201 | GPIO Access That May Sleep | |
202 | -------------------------- | |
203 | Some GPIO controllers must be accessed using message based buses like I2C or | |
204 | SPI. Commands to read or write those GPIO values require waiting to get to the | |
205 | head of a queue to transmit a command and get its response. This requires | |
206 | sleeping, which can't be done from inside IRQ handlers. | |
207 | ||
208 | Platforms that support this type of GPIO distinguish them from other GPIOs by | |
209 | returning nonzero from this call: | |
210 | ||
211 | int gpiod_cansleep(const struct gpio_desc *desc) | |
212 | ||
213 | To access such GPIOs, a different set of accessors is defined: | |
214 | ||
215 | int gpiod_get_value_cansleep(const struct gpio_desc *desc) | |
216 | void gpiod_set_value_cansleep(struct gpio_desc *desc, int value) | |
217 | ||
218 | Accessing such GPIOs requires a context which may sleep, for example a threaded | |
219 | IRQ handler, and those accessors must be used instead of spinlock-safe | |
220 | accessors without the cansleep() name suffix. | |
221 | ||
222 | Other than the fact that these accessors might sleep, and will work on GPIOs | |
223 | that can't be accessed from hardIRQ handlers, these calls act the same as the | |
224 | spinlock-safe calls. | |
225 | ||
226 | ||
227 | Active-low State and Raw GPIO Values | |
228 | ------------------------------------ | |
229 | Device drivers like to manage the logical state of a GPIO, i.e. the value their | |
230 | device will actually receive, no matter what lies between it and the GPIO line. | |
231 | In some cases, it might make sense to control the actual GPIO line value. The | |
232 | following set of calls ignore the active-low property of a GPIO and work on the | |
233 | raw line value: | |
234 | ||
235 | int gpiod_get_raw_value(const struct gpio_desc *desc) | |
236 | void gpiod_set_raw_value(struct gpio_desc *desc, int value) | |
237 | int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc) | |
238 | void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) | |
ef70bbe1 | 239 | int gpiod_direction_output_raw(struct gpio_desc *desc, int value) |
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240 | |
241 | The active-low state of a GPIO can also be queried using the following call: | |
242 | ||
243 | int gpiod_is_active_low(const struct gpio_desc *desc) | |
244 | ||
245 | Note that these functions should only be used with great moderation ; a driver | |
246 | should not have to care about the physical line level. | |
247 | ||
5f424243 | 248 | |
ac49fbd1 DB |
249 | The active-low property |
250 | ----------------------- | |
251 | ||
252 | As a driver should not have to care about the physical line level, all of the | |
253 | gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with | |
254 | the *logical* value. With this they take the active-low property into account. | |
255 | This means that they check whether the GPIO is configured to be active-low, | |
256 | and if so, they manipulate the passed value before the physical line level is | |
257 | driven. | |
258 | ||
259 | With this, all the gpiod_set_(array)_value_xxx() functions interpret the | |
260 | parameter "value" as "active" ("1") or "inactive" ("0"). The physical line | |
261 | level will be driven accordingly. | |
262 | ||
263 | As an example, if the active-low property for a dedicated GPIO is set, and the | |
264 | gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level | |
265 | will be driven low. | |
266 | ||
267 | To summarize: | |
268 | ||
547d4c10 | 269 | Function (example) active-low property physical line |
ac49fbd1 DB |
270 | gpiod_set_raw_value(desc, 0); don't care low |
271 | gpiod_set_raw_value(desc, 1); don't care high | |
272 | gpiod_set_value(desc, 0); default (active-high) low | |
273 | gpiod_set_value(desc, 1); default (active-high) high | |
274 | gpiod_set_value(desc, 0); active-low high | |
275 | gpiod_set_value(desc, 1); active-low low | |
276 | ||
277 | Please note again that the set_raw/get_raw functions should be avoided as much | |
278 | as possible, especially by drivers which should not care about the actual | |
279 | physical line level and worry about the logical value instead. | |
280 | ||
281 | ||
5f424243 RI |
282 | Set multiple GPIO outputs with a single function call |
283 | ----------------------------------------------------- | |
284 | The following functions set the output values of an array of GPIOs: | |
285 | ||
e2bfba41 RI |
286 | void gpiod_set_array_value(unsigned int array_size, |
287 | struct gpio_desc **desc_array, | |
288 | int *value_array) | |
289 | void gpiod_set_raw_array_value(unsigned int array_size, | |
290 | struct gpio_desc **desc_array, | |
291 | int *value_array) | |
292 | void gpiod_set_array_value_cansleep(unsigned int array_size, | |
293 | struct gpio_desc **desc_array, | |
294 | int *value_array) | |
295 | void gpiod_set_raw_array_value_cansleep(unsigned int array_size, | |
296 | struct gpio_desc **desc_array, | |
297 | int *value_array) | |
5f424243 RI |
298 | |
299 | The array can be an arbitrary set of GPIOs. The functions will try to set | |
300 | GPIOs belonging to the same bank or chip simultaneously if supported by the | |
301 | corresponding chip driver. In that case a significantly improved performance | |
302 | can be expected. If simultaneous setting is not possible the GPIOs will be set | |
303 | sequentially. | |
de3b6965 RI |
304 | |
305 | The gpiod_set_array() functions take three arguments: | |
306 | * array_size - the number of array elements | |
307 | * desc_array - an array of GPIO descriptors | |
308 | * value_array - an array of values to assign to the GPIOs | |
309 | ||
310 | The descriptor array can be obtained using the gpiod_get_array() function | |
311 | or one of its variants. If the group of descriptors returned by that function | |
312 | matches the desired group of GPIOs, those GPIOs can be set by simply using | |
313 | the struct gpio_descs returned by gpiod_get_array(): | |
314 | ||
315 | struct gpio_descs *my_gpio_descs = gpiod_get_array(...); | |
e2bfba41 RI |
316 | gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, |
317 | my_gpio_values); | |
de3b6965 RI |
318 | |
319 | It is also possible to set a completely arbitrary array of descriptors. The | |
320 | descriptors may be obtained using any combination of gpiod_get() and | |
321 | gpiod_get_array(). Afterwards the array of descriptors has to be setup | |
322 | manually before it can be used with gpiod_set_array(). | |
323 | ||
5f424243 RI |
324 | Note that for optimal performance GPIOs belonging to the same chip should be |
325 | contiguous within the array of descriptors. | |
326 | ||
327 | ||
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328 | GPIOs mapped to IRQs |
329 | -------------------- | |
330 | GPIO lines can quite often be used as IRQs. You can get the IRQ number | |
331 | corresponding to a given GPIO using the following call: | |
332 | ||
333 | int gpiod_to_irq(const struct gpio_desc *desc) | |
334 | ||
cbfa2c52 | 335 | It will return an IRQ number, or a negative errno code if the mapping can't be |
fd8e198c AC |
336 | done (most likely because that particular GPIO cannot be used as IRQ). It is an |
337 | unchecked error to use a GPIO that wasn't set up as an input using | |
338 | gpiod_direction_input(), or to use an IRQ number that didn't originally come | |
339 | from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. | |
340 | ||
341 | Non-error values returned from gpiod_to_irq() can be passed to request_irq() or | |
342 | free_irq(). They will often be stored into IRQ resources for platform devices, | |
343 | by the board-specific initialization code. Note that IRQ trigger options are | |
344 | part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup | |
345 | capabilities. | |
346 | ||
347 | ||
e36d453e RW |
348 | GPIOs and ACPI |
349 | ============== | |
350 | ||
351 | On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by | |
352 | the _CRS configuration objects of devices. Those resources do not provide | |
353 | connection IDs (names) for GPIOs, so it is necessary to use an additional | |
354 | mechanism for this purpose. | |
355 | ||
356 | Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object | |
357 | which, among other things, may be used to provide connection IDs for specific | |
358 | GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the | |
359 | case, it will be handled by the GPIO subsystem automatically. However, if the | |
360 | _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO | |
361 | connection IDs need to be provided by device drivers. | |
362 | ||
363 | For details refer to Documentation/acpi/gpio-properties.txt | |
364 | ||
365 | ||
fd8e198c AC |
366 | Interacting With the Legacy GPIO Subsystem |
367 | ========================================== | |
368 | Many kernel subsystems still handle GPIOs using the legacy integer-based | |
369 | interface. Although it is strongly encouraged to upgrade them to the safer | |
370 | descriptor-based API, the following two functions allow you to convert a GPIO | |
371 | descriptor into the GPIO integer namespace and vice-versa: | |
372 | ||
373 | int desc_to_gpio(const struct gpio_desc *desc) | |
374 | struct gpio_desc *gpio_to_desc(unsigned gpio) | |
375 | ||
376 | The GPIO number returned by desc_to_gpio() can be safely used as long as the | |
377 | GPIO descriptor has not been freed. All the same, a GPIO number passed to | |
378 | gpio_to_desc() must have been properly acquired, and usage of the returned GPIO | |
379 | descriptor is only possible after the GPIO number has been released. | |
380 | ||
381 | Freeing a GPIO obtained by one API with the other API is forbidden and an | |
382 | unchecked error. |