1 ================================== 1 ==================================
2 GPIO Descriptor Consumer Interface 2 GPIO Descriptor Consumer Interface
3 ================================== 3 ==================================
4 4
5 This document describes the consumer interface !! 5 This document describes the consumer interface of the GPIO framework. Note that
>> 6 it describes the new descriptor-based interface. For a description of the
>> 7 deprecated integer-based GPIO interface please refer to gpio-legacy.txt.
6 8
7 9
8 Guidelines for GPIOs consumers 10 Guidelines for GPIOs consumers
9 ============================== 11 ==============================
10 12
11 Drivers that can't work without standard GPIO 13 Drivers that can't work without standard GPIO calls should have Kconfig entries
12 that depend on GPIOLIB or select GPIOLIB. The 14 that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to
13 obtain and use GPIOs are available by includin 15 obtain and use GPIOs are available by including the following file::
14 16
15 #include <linux/gpio/consumer.h> 17 #include <linux/gpio/consumer.h>
16 18
17 There are static inline stubs for all function 19 There are static inline stubs for all functions in the header file in the case
18 where GPIOLIB is disabled. When these stubs ar 20 where GPIOLIB is disabled. When these stubs are called they will emit
19 warnings. These stubs are used for two use cas 21 warnings. These stubs are used for two use cases:
20 22
21 - Simple compile coverage with e.g. COMPILE_TE 23 - Simple compile coverage with e.g. COMPILE_TEST - it does not matter that
22 the current platform does not enable or sele 24 the current platform does not enable or select GPIOLIB because we are not
23 going to execute the system anyway. 25 going to execute the system anyway.
24 26
25 - Truly optional GPIOLIB support - where the d 27 - Truly optional GPIOLIB support - where the driver does not really make use
26 of the GPIOs on certain compile-time configu 28 of the GPIOs on certain compile-time configurations for certain systems, but
27 will use it under other compile-time configu 29 will use it under other compile-time configurations. In this case the
28 consumer must make sure not to call into the 30 consumer must make sure not to call into these functions, or the user will
29 be met with console warnings that may be per 31 be met with console warnings that may be perceived as intimidating.
30 Combining truly optional GPIOLIB usage with <<
31 ``[devm_]gpiod_get_optional()`` is a *bad id <<
32 error messages. Use the ordinary getter func <<
33 some open coding of error handling should be <<
34 32
35 All the functions that work with the descripto 33 All the functions that work with the descriptor-based GPIO interface are
36 prefixed with ``gpiod_``. The ``gpio_`` prefix 34 prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
37 interface. No other function in the kernel sho 35 interface. No other function in the kernel should use these prefixes. The use
38 of the legacy functions is strongly discourage 36 of the legacy functions is strongly discouraged, new code should use
39 <linux/gpio/consumer.h> and descriptors exclus 37 <linux/gpio/consumer.h> and descriptors exclusively.
40 38
41 39
42 Obtaining and Disposing GPIOs 40 Obtaining and Disposing GPIOs
43 ============================= 41 =============================
44 42
45 With the descriptor-based interface, GPIOs are 43 With the descriptor-based interface, GPIOs are identified with an opaque,
46 non-forgeable handler that must be obtained th 44 non-forgeable handler that must be obtained through a call to one of the
47 gpiod_get() functions. Like many other kernel 45 gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
48 device that will use the GPIO and the function 46 device that will use the GPIO and the function the requested GPIO is supposed to
49 fulfill:: 47 fulfill::
50 48
51 struct gpio_desc *gpiod_get(struct dev 49 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
52 enum gpiod 50 enum gpiod_flags flags)
53 51
54 If a function is implemented by using several 52 If a function is implemented by using several GPIOs together (e.g. a simple LED
55 device that displays digits), an additional in 53 device that displays digits), an additional index argument can be specified::
56 54
57 struct gpio_desc *gpiod_get_index(stru 55 struct gpio_desc *gpiod_get_index(struct device *dev,
58 cons 56 const char *con_id, unsigned int idx,
59 enum 57 enum gpiod_flags flags)
60 58
61 For a more detailed description of the con_id 59 For a more detailed description of the con_id parameter in the DeviceTree case
62 see Documentation/driver-api/gpio/board.rst 60 see Documentation/driver-api/gpio/board.rst
63 61
64 The flags parameter is used to optionally spec 62 The flags parameter is used to optionally specify a direction and initial value
65 for the GPIO. Values can be: 63 for the GPIO. Values can be:
66 64
67 * GPIOD_ASIS or 0 to not initialize the GPIO a 65 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
68 later with one of the dedicated functions. 66 later with one of the dedicated functions.
69 * GPIOD_IN to initialize the GPIO as input. 67 * GPIOD_IN to initialize the GPIO as input.
70 * GPIOD_OUT_LOW to initialize the GPIO as outp 68 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
71 * GPIOD_OUT_HIGH to initialize the GPIO as out 69 * GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1.
72 * GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_L 70 * GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
73 to be electrically used with open drain. 71 to be electrically used with open drain.
74 * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_ 72 * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
75 to be electrically used with open drain. 73 to be electrically used with open drain.
76 74
77 Note that the initial value is *logical* and t 75 Note that the initial value is *logical* and the physical line level depends on
78 whether the line is configured active high or 76 whether the line is configured active high or active low (see
79 :ref:`active_low_semantics`). 77 :ref:`active_low_semantics`).
80 78
81 The two last flags are used for use cases wher 79 The two last flags are used for use cases where open drain is mandatory, such
82 as I2C: if the line is not already configured 80 as I2C: if the line is not already configured as open drain in the mappings
83 (see board.rst), then open drain will be enfor !! 81 (see board.txt), then open drain will be enforced anyway and a warning will be
84 printed that the board configuration needs to 82 printed that the board configuration needs to be updated to match the use case.
85 83
86 Both functions return either a valid GPIO desc 84 Both functions return either a valid GPIO descriptor, or an error code checkable
87 with IS_ERR() (they will never return a NULL p 85 with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned
88 if and only if no GPIO has been assigned to th 86 if and only if no GPIO has been assigned to the device/function/index triplet,
89 other error codes are used for cases where a G 87 other error codes are used for cases where a GPIO has been assigned but an error
90 occurred while trying to acquire it. This is u 88 occurred while trying to acquire it. This is useful to discriminate between mere
91 errors and an absence of GPIO for optional GPI 89 errors and an absence of GPIO for optional GPIO parameters. For the common
92 pattern where a GPIO is optional, the gpiod_ge 90 pattern where a GPIO is optional, the gpiod_get_optional() and
93 gpiod_get_index_optional() functions can be us 91 gpiod_get_index_optional() functions can be used. These functions return NULL
94 instead of -ENOENT if no GPIO has been assigne 92 instead of -ENOENT if no GPIO has been assigned to the requested function::
95 93
96 struct gpio_desc *gpiod_get_optional(s 94 struct gpio_desc *gpiod_get_optional(struct device *dev,
97 c 95 const char *con_id,
98 e 96 enum gpiod_flags flags)
99 97
100 struct gpio_desc *gpiod_get_index_opti 98 struct gpio_desc *gpiod_get_index_optional(struct device *dev,
101 99 const char *con_id,
102 100 unsigned int index,
103 101 enum gpiod_flags flags)
104 102
105 Note that gpio_get*_optional() functions (and 103 Note that gpio_get*_optional() functions (and their managed variants), unlike
106 the rest of gpiolib API, also return NULL when 104 the rest of gpiolib API, also return NULL when gpiolib support is disabled.
107 This is helpful to driver authors, since they 105 This is helpful to driver authors, since they do not need to special case
108 -ENOSYS return codes. System integrators shou 106 -ENOSYS return codes. System integrators should however be careful to enable
109 gpiolib on systems that need it. 107 gpiolib on systems that need it.
110 108
111 For a function using multiple GPIOs all of tho 109 For a function using multiple GPIOs all of those can be obtained with one call::
112 110
113 struct gpio_descs *gpiod_get_array(str 111 struct gpio_descs *gpiod_get_array(struct device *dev,
114 con 112 const char *con_id,
115 enu 113 enum gpiod_flags flags)
116 114
117 This function returns a struct gpio_descs whic 115 This function returns a struct gpio_descs which contains an array of
118 descriptors. It also contains a pointer to a 116 descriptors. It also contains a pointer to a gpiolib private structure which,
119 if passed back to get/set array functions, may !! 117 if passed back to get/set array functions, may speed up I/O proocessing::
120 118
121 struct gpio_descs { 119 struct gpio_descs {
122 struct gpio_array *info; 120 struct gpio_array *info;
123 unsigned int ndescs; 121 unsigned int ndescs;
124 struct gpio_desc *desc[]; 122 struct gpio_desc *desc[];
125 } 123 }
126 124
127 The following function returns NULL instead of 125 The following function returns NULL instead of -ENOENT if no GPIOs have been
128 assigned to the requested function:: 126 assigned to the requested function::
129 127
130 struct gpio_descs *gpiod_get_array_opt 128 struct gpio_descs *gpiod_get_array_optional(struct device *dev,
131 129 const char *con_id,
132 130 enum gpiod_flags flags)
133 131
134 Device-managed variants of these functions are 132 Device-managed variants of these functions are also defined::
135 133
136 struct gpio_desc *devm_gpiod_get(struc 134 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
137 enum 135 enum gpiod_flags flags)
138 136
139 struct gpio_desc *devm_gpiod_get_index 137 struct gpio_desc *devm_gpiod_get_index(struct device *dev,
140 138 const char *con_id,
141 139 unsigned int idx,
142 140 enum gpiod_flags flags)
143 141
144 struct gpio_desc *devm_gpiod_get_optio 142 struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
145 143 const char *con_id,
146 144 enum gpiod_flags flags)
147 145
148 struct gpio_desc *devm_gpiod_get_index 146 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
149 147 const char *con_id,
150 148 unsigned int index,
151 149 enum gpiod_flags flags)
152 150
153 struct gpio_descs *devm_gpiod_get_arra 151 struct gpio_descs *devm_gpiod_get_array(struct device *dev,
154 152 const char *con_id,
155 153 enum gpiod_flags flags)
156 154
157 struct gpio_descs *devm_gpiod_get_arra 155 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
158 156 const char *con_id,
159 157 enum gpiod_flags flags)
160 158
161 A GPIO descriptor can be disposed of using the 159 A GPIO descriptor can be disposed of using the gpiod_put() function::
162 160
163 void gpiod_put(struct gpio_desc *desc) 161 void gpiod_put(struct gpio_desc *desc)
164 162
165 For an array of GPIOs this function can be use 163 For an array of GPIOs this function can be used::
166 164
167 void gpiod_put_array(struct gpio_descs 165 void gpiod_put_array(struct gpio_descs *descs)
168 166
169 It is strictly forbidden to use a descriptor a 167 It is strictly forbidden to use a descriptor after calling these functions.
170 It is also not allowed to individually release 168 It is also not allowed to individually release descriptors (using gpiod_put())
171 from an array acquired with gpiod_get_array(). 169 from an array acquired with gpiod_get_array().
172 170
173 The device-managed variants are, unsurprisingl 171 The device-managed variants are, unsurprisingly::
174 172
175 void devm_gpiod_put(struct device *dev 173 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
176 174
177 void devm_gpiod_put_array(struct devic 175 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
178 176
179 177
180 Using GPIOs 178 Using GPIOs
181 =========== 179 ===========
182 180
183 Setting Direction 181 Setting Direction
184 ----------------- 182 -----------------
185 The first thing a driver must do with a GPIO i 183 The first thing a driver must do with a GPIO is setting its direction. If no
186 direction-setting flags have been given to gpi 184 direction-setting flags have been given to gpiod_get*(), this is done by
187 invoking one of the gpiod_direction_*() functi 185 invoking one of the gpiod_direction_*() functions::
188 186
189 int gpiod_direction_input(struct gpio_ 187 int gpiod_direction_input(struct gpio_desc *desc)
190 int gpiod_direction_output(struct gpio 188 int gpiod_direction_output(struct gpio_desc *desc, int value)
191 189
192 The return value is zero for success, else a n 190 The return value is zero for success, else a negative errno. It should be
193 checked, since the get/set calls don't return 191 checked, since the get/set calls don't return errors and since misconfiguration
194 is possible. You should normally issue these c 192 is possible. You should normally issue these calls from a task context. However,
195 for spinlock-safe GPIOs it is OK to use them b 193 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
196 of early board setup. 194 of early board setup.
197 195
198 For output GPIOs, the value provided becomes t 196 For output GPIOs, the value provided becomes the initial output value. This
199 helps avoid signal glitching during system sta 197 helps avoid signal glitching during system startup.
200 198
201 A driver can also query the current direction 199 A driver can also query the current direction of a GPIO::
202 200
203 int gpiod_get_direction(const struct g 201 int gpiod_get_direction(const struct gpio_desc *desc)
204 202
205 This function returns 0 for output, 1 for inpu 203 This function returns 0 for output, 1 for input, or an error code in case of error.
206 204
207 Be aware that there is no default direction fo 205 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
208 without setting its direction first is illegal 206 without setting its direction first is illegal and will result in undefined
209 behavior!** 207 behavior!**
210 208
211 209
212 Spinlock-Safe GPIO Access 210 Spinlock-Safe GPIO Access
213 ------------------------- 211 -------------------------
214 Most GPIO controllers can be accessed with mem 212 Most GPIO controllers can be accessed with memory read/write instructions. Those
215 don't need to sleep, and can safely be done fr 213 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
216 handlers and similar contexts. 214 handlers and similar contexts.
217 215
218 Use the following calls to access GPIOs from a 216 Use the following calls to access GPIOs from an atomic context::
219 217
220 int gpiod_get_value(const struct gpio_ 218 int gpiod_get_value(const struct gpio_desc *desc);
221 void gpiod_set_value(struct gpio_desc 219 void gpiod_set_value(struct gpio_desc *desc, int value);
222 220
223 The values are boolean, zero for inactive, non !! 221 The values are boolean, zero for low, nonzero for high. When reading the value
224 value of an output pin, the value returned sho !! 222 of an output pin, the value returned should be what's seen on the pin. That
225 That won't always match the specified output v !! 223 won't always match the specified output value, because of issues including
226 open-drain signaling and output latencies. 224 open-drain signaling and output latencies.
227 225
228 The get/set calls do not return errors because 226 The get/set calls do not return errors because "invalid GPIO" should have been
229 reported earlier from gpiod_direction_*(). How 227 reported earlier from gpiod_direction_*(). However, note that not all platforms
230 can read the value of output pins; those that 228 can read the value of output pins; those that can't should always return zero.
231 Also, using these calls for GPIOs that can't s 229 Also, using these calls for GPIOs that can't safely be accessed without sleeping
232 (see below) is an error. 230 (see below) is an error.
233 231
234 232
235 GPIO Access That May Sleep 233 GPIO Access That May Sleep
236 -------------------------- 234 --------------------------
237 Some GPIO controllers must be accessed using m 235 Some GPIO controllers must be accessed using message based buses like I2C or
238 SPI. Commands to read or write those GPIO valu 236 SPI. Commands to read or write those GPIO values require waiting to get to the
239 head of a queue to transmit a command and get 237 head of a queue to transmit a command and get its response. This requires
240 sleeping, which can't be done from inside IRQ 238 sleeping, which can't be done from inside IRQ handlers.
241 239
242 Platforms that support this type of GPIO disti 240 Platforms that support this type of GPIO distinguish them from other GPIOs by
243 returning nonzero from this call:: 241 returning nonzero from this call::
244 242
245 int gpiod_cansleep(const struct gpio_d 243 int gpiod_cansleep(const struct gpio_desc *desc)
246 244
247 To access such GPIOs, a different set of acces 245 To access such GPIOs, a different set of accessors is defined::
248 246
249 int gpiod_get_value_cansleep(const str 247 int gpiod_get_value_cansleep(const struct gpio_desc *desc)
250 void gpiod_set_value_cansleep(struct g 248 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
251 249
252 Accessing such GPIOs requires a context which 250 Accessing such GPIOs requires a context which may sleep, for example a threaded
253 IRQ handler, and those accessors must be used 251 IRQ handler, and those accessors must be used instead of spinlock-safe
254 accessors without the cansleep() name suffix. 252 accessors without the cansleep() name suffix.
255 253
256 Other than the fact that these accessors might 254 Other than the fact that these accessors might sleep, and will work on GPIOs
257 that can't be accessed from hardIRQ handlers, 255 that can't be accessed from hardIRQ handlers, these calls act the same as the
258 spinlock-safe calls. 256 spinlock-safe calls.
259 257
260 258
261 .. _active_low_semantics: 259 .. _active_low_semantics:
262 260
263 The active low and open drain semantics 261 The active low and open drain semantics
264 --------------------------------------- 262 ---------------------------------------
265 As a consumer should not have to care about th 263 As a consumer should not have to care about the physical line level, all of the
266 gpiod_set_value_xxx() or gpiod_set_array_value 264 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
267 the *logical* value. With this they take the a 265 the *logical* value. With this they take the active low property into account.
268 This means that they check whether the GPIO is 266 This means that they check whether the GPIO is configured to be active low,
269 and if so, they manipulate the passed value be 267 and if so, they manipulate the passed value before the physical line level is
270 driven. 268 driven.
271 269
272 The same is applicable for open drain or open 270 The same is applicable for open drain or open source output lines: those do not
273 actively drive their output high (open drain) 271 actively drive their output high (open drain) or low (open source), they just
274 switch their output to a high impedance value. 272 switch their output to a high impedance value. The consumer should not need to
275 care. (For details read about open drain in dr !! 273 care. (For details read about open drain in driver.txt.)
276 274
277 With this, all the gpiod_set_(array)_value_xxx 275 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
278 parameter "value" as "active" ("1") or "inacti !! 276 parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line
279 level will be driven accordingly. 277 level will be driven accordingly.
280 278
281 As an example, if the active low property for 279 As an example, if the active low property for a dedicated GPIO is set, and the
282 gpiod_set_(array)_value_xxx() passes "active" !! 280 gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level
283 will be driven low. 281 will be driven low.
284 282
285 To summarize:: 283 To summarize::
286 284
287 Function (example) line prop 285 Function (example) line property physical line
288 gpiod_set_raw_value(desc, 0); don't car 286 gpiod_set_raw_value(desc, 0); don't care low
289 gpiod_set_raw_value(desc, 1); don't car 287 gpiod_set_raw_value(desc, 1); don't care high
290 gpiod_set_value(desc, 0); default ( 288 gpiod_set_value(desc, 0); default (active high) low
291 gpiod_set_value(desc, 1); default ( 289 gpiod_set_value(desc, 1); default (active high) high
292 gpiod_set_value(desc, 0); active lo 290 gpiod_set_value(desc, 0); active low high
293 gpiod_set_value(desc, 1); active lo 291 gpiod_set_value(desc, 1); active low low
294 gpiod_set_value(desc, 0); open drai 292 gpiod_set_value(desc, 0); open drain low
295 gpiod_set_value(desc, 1); open drai 293 gpiod_set_value(desc, 1); open drain high impedance
296 gpiod_set_value(desc, 0); open sour 294 gpiod_set_value(desc, 0); open source high impedance
297 gpiod_set_value(desc, 1); open sour 295 gpiod_set_value(desc, 1); open source high
298 296
299 It is possible to override these semantics usi 297 It is possible to override these semantics using the set_raw/get_raw functions
300 but it should be avoided as much as possible, 298 but it should be avoided as much as possible, especially by system-agnostic drivers
301 which should not need to care about the actual 299 which should not need to care about the actual physical line level and worry about
302 the logical value instead. 300 the logical value instead.
303 301
304 302
305 Accessing raw GPIO values 303 Accessing raw GPIO values
306 ------------------------- 304 -------------------------
307 Consumers exist that need to manage the logica 305 Consumers exist that need to manage the logical state of a GPIO line, i.e. the value
308 their device will actually receive, no matter 306 their device will actually receive, no matter what lies between it and the GPIO
309 line. 307 line.
310 308
311 The following set of calls ignore the active-l 309 The following set of calls ignore the active-low or open drain property of a GPIO and
312 work on the raw line value:: 310 work on the raw line value::
313 311
314 int gpiod_get_raw_value(const struct g 312 int gpiod_get_raw_value(const struct gpio_desc *desc)
315 void gpiod_set_raw_value(struct gpio_d 313 void gpiod_set_raw_value(struct gpio_desc *desc, int value)
316 int gpiod_get_raw_value_cansleep(const 314 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
317 void gpiod_set_raw_value_cansleep(stru 315 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
318 int gpiod_direction_output_raw(struct 316 int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
319 317
320 The active low state of a GPIO can also be que 318 The active low state of a GPIO can also be queried and toggled using the
321 following calls:: 319 following calls::
322 320
323 int gpiod_is_active_low(const struct g 321 int gpiod_is_active_low(const struct gpio_desc *desc)
324 void gpiod_toggle_active_low(struct gp 322 void gpiod_toggle_active_low(struct gpio_desc *desc)
325 323
326 Note that these functions should only be used 324 Note that these functions should only be used with great moderation; a driver
327 should not have to care about the physical lin 325 should not have to care about the physical line level or open drain semantics.
328 326
329 327
330 Access multiple GPIOs with a single function c 328 Access multiple GPIOs with a single function call
331 ---------------------------------------------- 329 -------------------------------------------------
332 The following functions get or set the values 330 The following functions get or set the values of an array of GPIOs::
333 331
334 int gpiod_get_array_value(unsigned int 332 int gpiod_get_array_value(unsigned int array_size,
335 struct gpio_ 333 struct gpio_desc **desc_array,
336 struct gpio_ 334 struct gpio_array *array_info,
337 unsigned lon 335 unsigned long *value_bitmap);
338 int gpiod_get_raw_array_value(unsigned 336 int gpiod_get_raw_array_value(unsigned int array_size,
339 struct g 337 struct gpio_desc **desc_array,
340 struct g 338 struct gpio_array *array_info,
341 unsigned 339 unsigned long *value_bitmap);
342 int gpiod_get_array_value_cansleep(uns 340 int gpiod_get_array_value_cansleep(unsigned int array_size,
343 str 341 struct gpio_desc **desc_array,
344 str 342 struct gpio_array *array_info,
345 uns 343 unsigned long *value_bitmap);
346 int gpiod_get_raw_array_value_cansleep 344 int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
347 str 345 struct gpio_desc **desc_array,
348 str 346 struct gpio_array *array_info,
349 uns 347 unsigned long *value_bitmap);
350 348
351 int gpiod_set_array_value(unsigned int 349 int gpiod_set_array_value(unsigned int array_size,
352 struct gpio_ 350 struct gpio_desc **desc_array,
353 struct gpio_ 351 struct gpio_array *array_info,
354 unsigned lon 352 unsigned long *value_bitmap)
355 int gpiod_set_raw_array_value(unsigned 353 int gpiod_set_raw_array_value(unsigned int array_size,
356 struct g 354 struct gpio_desc **desc_array,
357 struct g 355 struct gpio_array *array_info,
358 unsigned 356 unsigned long *value_bitmap)
359 int gpiod_set_array_value_cansleep(uns 357 int gpiod_set_array_value_cansleep(unsigned int array_size,
360 str 358 struct gpio_desc **desc_array,
361 str 359 struct gpio_array *array_info,
362 uns 360 unsigned long *value_bitmap)
363 int gpiod_set_raw_array_value_cansleep 361 int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
364 362 struct gpio_desc **desc_array,
365 363 struct gpio_array *array_info,
366 364 unsigned long *value_bitmap)
367 365
368 The array can be an arbitrary set of GPIOs. Th 366 The array can be an arbitrary set of GPIOs. The functions will try to access
369 GPIOs belonging to the same bank or chip simul 367 GPIOs belonging to the same bank or chip simultaneously if supported by the
370 corresponding chip driver. In that case a sign 368 corresponding chip driver. In that case a significantly improved performance
371 can be expected. If simultaneous access is not 369 can be expected. If simultaneous access is not possible the GPIOs will be
372 accessed sequentially. 370 accessed sequentially.
373 371
374 The functions take four arguments: 372 The functions take four arguments:
375 373
376 * array_size - the number of array 374 * array_size - the number of array elements
377 * desc_array - an array of GPIO des 375 * desc_array - an array of GPIO descriptors
378 * array_info - optional information 376 * array_info - optional information obtained from gpiod_get_array()
379 * value_bitmap - a bitmap to store th 377 * value_bitmap - a bitmap to store the GPIOs' values (get) or
380 a bitmap of values to assign to the 378 a bitmap of values to assign to the GPIOs (set)
381 379
382 The descriptor array can be obtained using the 380 The descriptor array can be obtained using the gpiod_get_array() function
383 or one of its variants. If the group of descri 381 or one of its variants. If the group of descriptors returned by that function
384 matches the desired group of GPIOs, those GPIO 382 matches the desired group of GPIOs, those GPIOs can be accessed by simply using
385 the struct gpio_descs returned by gpiod_get_ar 383 the struct gpio_descs returned by gpiod_get_array()::
386 384
387 struct gpio_descs *my_gpio_descs = gpi 385 struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
388 gpiod_set_array_value(my_gpio_descs->n 386 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
389 my_gpio_descs->i 387 my_gpio_descs->info, my_gpio_value_bitmap);
390 388
391 It is also possible to access a completely arb 389 It is also possible to access a completely arbitrary array of descriptors. The
392 descriptors may be obtained using any combinat 390 descriptors may be obtained using any combination of gpiod_get() and
393 gpiod_get_array(). Afterwards the array of des 391 gpiod_get_array(). Afterwards the array of descriptors has to be setup
394 manually before it can be passed to one of the 392 manually before it can be passed to one of the above functions. In that case,
395 array_info should be set to NULL. 393 array_info should be set to NULL.
396 394
397 Note that for optimal performance GPIOs belong 395 Note that for optimal performance GPIOs belonging to the same chip should be
398 contiguous within the array of descriptors. 396 contiguous within the array of descriptors.
399 397
400 Still better performance may be achieved if ar 398 Still better performance may be achieved if array indexes of the descriptors
401 match hardware pin numbers of a single chip. 399 match hardware pin numbers of a single chip. If an array passed to a get/set
402 array function matches the one obtained from g 400 array function matches the one obtained from gpiod_get_array() and array_info
403 associated with the array is also passed, the 401 associated with the array is also passed, the function may take a fast bitmap
404 processing path, passing the value_bitmap argu 402 processing path, passing the value_bitmap argument directly to the respective
405 .get/set_multiple() callback of the chip. Tha 403 .get/set_multiple() callback of the chip. That allows for utilization of GPIO
406 banks as data I/O ports without much loss of p 404 banks as data I/O ports without much loss of performance.
407 405
408 The return value of gpiod_get_array_value() an 406 The return value of gpiod_get_array_value() and its variants is 0 on success
409 or negative on error. Note the difference to g 407 or negative on error. Note the difference to gpiod_get_value(), which returns
410 0 or 1 on success to convey the GPIO value. Wi 408 0 or 1 on success to convey the GPIO value. With the array functions, the GPIO
411 values are stored in value_array rather than p 409 values are stored in value_array rather than passed back as return value.
412 410
413 411
414 GPIOs mapped to IRQs 412 GPIOs mapped to IRQs
415 -------------------- 413 --------------------
416 GPIO lines can quite often be used as IRQs. Yo 414 GPIO lines can quite often be used as IRQs. You can get the IRQ number
417 corresponding to a given GPIO using the follow 415 corresponding to a given GPIO using the following call::
418 416
419 int gpiod_to_irq(const struct gpio_des 417 int gpiod_to_irq(const struct gpio_desc *desc)
420 418
421 It will return an IRQ number, or a negative er 419 It will return an IRQ number, or a negative errno code if the mapping can't be
422 done (most likely because that particular GPIO 420 done (most likely because that particular GPIO cannot be used as IRQ). It is an
423 unchecked error to use a GPIO that wasn't set 421 unchecked error to use a GPIO that wasn't set up as an input using
424 gpiod_direction_input(), or to use an IRQ numb 422 gpiod_direction_input(), or to use an IRQ number that didn't originally come
425 from gpiod_to_irq(). gpiod_to_irq() is not all 423 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
426 424
427 Non-error values returned from gpiod_to_irq() 425 Non-error values returned from gpiod_to_irq() can be passed to request_irq() or
428 free_irq(). They will often be stored into IRQ 426 free_irq(). They will often be stored into IRQ resources for platform devices,
429 by the board-specific initialization code. Not 427 by the board-specific initialization code. Note that IRQ trigger options are
430 part of the IRQ interface, e.g. IRQF_TRIGGER_F 428 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
431 capabilities. 429 capabilities.
432 430
433 431
434 GPIOs and ACPI 432 GPIOs and ACPI
435 ============== 433 ==============
436 434
437 On ACPI systems, GPIOs are described by GpioIo 435 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
438 the _CRS configuration objects of devices. Th 436 the _CRS configuration objects of devices. Those resources do not provide
439 connection IDs (names) for GPIOs, so it is nec 437 connection IDs (names) for GPIOs, so it is necessary to use an additional
440 mechanism for this purpose. 438 mechanism for this purpose.
441 439
442 Systems compliant with ACPI 5.1 or newer may p 440 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
443 which, among other things, may be used to prov 441 which, among other things, may be used to provide connection IDs for specific
444 GPIOs described by the GpioIo()/GpioInt() reso 442 GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the
445 case, it will be handled by the GPIO subsystem 443 case, it will be handled by the GPIO subsystem automatically. However, if the
446 _DSD is not present, the mappings between Gpio 444 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
447 connection IDs need to be provided by device d 445 connection IDs need to be provided by device drivers.
448 446
449 For details refer to Documentation/firmware-gu 447 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
450 448
451 449
452 Interacting With the Legacy GPIO Subsystem 450 Interacting With the Legacy GPIO Subsystem
453 ========================================== 451 ==========================================
454 Many kernel subsystems and drivers still handl 452 Many kernel subsystems and drivers still handle GPIOs using the legacy
455 integer-based interface. It is strongly recomm 453 integer-based interface. It is strongly recommended to update these to the new
456 gpiod interface. For cases where both interfac 454 gpiod interface. For cases where both interfaces need to be used, the following
457 two functions allow to convert a GPIO descript 455 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
458 and vice-versa:: 456 and vice-versa::
459 457
460 int desc_to_gpio(const struct gpio_des 458 int desc_to_gpio(const struct gpio_desc *desc)
461 struct gpio_desc *gpio_to_desc(unsigne 459 struct gpio_desc *gpio_to_desc(unsigned gpio)
462 460
463 The GPIO number returned by desc_to_gpio() can 461 The GPIO number returned by desc_to_gpio() can safely be used as a parameter of
464 the gpio\_*() functions for as long as the GPI 462 the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed.
465 All the same, a GPIO number passed to gpio_to_ 463 All the same, a GPIO number passed to gpio_to_desc() must first be properly
466 acquired using e.g. gpio_request_one(), and th 464 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
467 considered valid until that GPIO number is rel 465 considered valid until that GPIO number is released using gpio_free().
468 466
469 Freeing a GPIO obtained by one API with the ot 467 Freeing a GPIO obtained by one API with the other API is forbidden and an
470 unchecked error. 468 unchecked error.
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