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Linux/Documentation/driver-api/gpio/consumer.rst

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Diff markup

Differences between /Documentation/driver-api/gpio/consumer.rst (Version linux-6.12-rc7) and /Documentation/driver-api/gpio/consumer.rst (Version linux-6.10.14)


  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 legacy.rst.
  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      32   Combining truly optional GPIOLIB usage with calls to
 31   ``[devm_]gpiod_get_optional()`` is a *bad id     33   ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird
 32   error messages. Use the ordinary getter func     34   error messages. Use the ordinary getter functions with optional GPIOLIB:
 33   some open coding of error handling should be     35   some open coding of error handling should be expected when you do this.
 34                                                    36 
 35 All the functions that work with the descripto     37 All the functions that work with the descriptor-based GPIO interface are
 36 prefixed with ``gpiod_``. The ``gpio_`` prefix     38 prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy
 37 interface. No other function in the kernel sho     39 interface. No other function in the kernel should use these prefixes. The use
 38 of the legacy functions is strongly discourage     40 of the legacy functions is strongly discouraged, new code should use
 39 <linux/gpio/consumer.h> and descriptors exclus     41 <linux/gpio/consumer.h> and descriptors exclusively.
 40                                                    42 
 41                                                    43 
 42 Obtaining and Disposing GPIOs                      44 Obtaining and Disposing GPIOs
 43 =============================                      45 =============================
 44                                                    46 
 45 With the descriptor-based interface, GPIOs are     47 With the descriptor-based interface, GPIOs are identified with an opaque,
 46 non-forgeable handler that must be obtained th     48 non-forgeable handler that must be obtained through a call to one of the
 47 gpiod_get() functions. Like many other kernel      49 gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the
 48 device that will use the GPIO and the function     50 device that will use the GPIO and the function the requested GPIO is supposed to
 49 fulfill::                                          51 fulfill::
 50                                                    52 
 51         struct gpio_desc *gpiod_get(struct dev     53         struct gpio_desc *gpiod_get(struct device *dev, const char *con_id,
 52                                     enum gpiod     54                                     enum gpiod_flags flags)
 53                                                    55 
 54 If a function is implemented by using several      56 If a function is implemented by using several GPIOs together (e.g. a simple LED
 55 device that displays digits), an additional in     57 device that displays digits), an additional index argument can be specified::
 56                                                    58 
 57         struct gpio_desc *gpiod_get_index(stru     59         struct gpio_desc *gpiod_get_index(struct device *dev,
 58                                           cons     60                                           const char *con_id, unsigned int idx,
 59                                           enum     61                                           enum gpiod_flags flags)
 60                                                    62 
 61 For a more detailed description of the con_id      63 For a more detailed description of the con_id parameter in the DeviceTree case
 62 see Documentation/driver-api/gpio/board.rst        64 see Documentation/driver-api/gpio/board.rst
 63                                                    65 
 64 The flags parameter is used to optionally spec     66 The flags parameter is used to optionally specify a direction and initial value
 65 for the GPIO. Values can be:                       67 for the GPIO. Values can be:
 66                                                    68 
 67 * GPIOD_ASIS or 0 to not initialize the GPIO a     69 * GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set
 68   later with one of the dedicated functions.       70   later with one of the dedicated functions.
 69 * GPIOD_IN to initialize the GPIO as input.        71 * GPIOD_IN to initialize the GPIO as input.
 70 * GPIOD_OUT_LOW to initialize the GPIO as outp     72 * GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0.
 71 * GPIOD_OUT_HIGH to initialize the GPIO as out     73 * 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     74 * GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line
 73   to be electrically used with open drain.         75   to be electrically used with open drain.
 74 * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_     76 * GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line
 75   to be electrically used with open drain.         77   to be electrically used with open drain.
 76                                                    78 
 77 Note that the initial value is *logical* and t     79 Note that the initial value is *logical* and the physical line level depends on
 78 whether the line is configured active high or      80 whether the line is configured active high or active low (see
 79 :ref:`active_low_semantics`).                      81 :ref:`active_low_semantics`).
 80                                                    82 
 81 The two last flags are used for use cases wher     83 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      84 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     85 (see board.rst), then open drain will be enforced anyway and a warning will be
 84 printed that the board configuration needs to      86 printed that the board configuration needs to be updated to match the use case.
 85                                                    87 
 86 Both functions return either a valid GPIO desc     88 Both functions return either a valid GPIO descriptor, or an error code checkable
 87 with IS_ERR() (they will never return a NULL p     89 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     90 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     91 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     92 occurred while trying to acquire it. This is useful to discriminate between mere
 91 errors and an absence of GPIO for optional GPI     93 errors and an absence of GPIO for optional GPIO parameters. For the common
 92 pattern where a GPIO is optional, the gpiod_ge     94 pattern where a GPIO is optional, the gpiod_get_optional() and
 93 gpiod_get_index_optional() functions can be us     95 gpiod_get_index_optional() functions can be used. These functions return NULL
 94 instead of -ENOENT if no GPIO has been assigne     96 instead of -ENOENT if no GPIO has been assigned to the requested function::
 95                                                    97 
 96         struct gpio_desc *gpiod_get_optional(s     98         struct gpio_desc *gpiod_get_optional(struct device *dev,
 97                                              c     99                                              const char *con_id,
 98                                              e    100                                              enum gpiod_flags flags)
 99                                                   101 
100         struct gpio_desc *gpiod_get_index_opti    102         struct gpio_desc *gpiod_get_index_optional(struct device *dev,
101                                                   103                                                    const char *con_id,
102                                                   104                                                    unsigned int index,
103                                                   105                                                    enum gpiod_flags flags)
104                                                   106 
105 Note that gpio_get*_optional() functions (and     107 Note that gpio_get*_optional() functions (and their managed variants), unlike
106 the rest of gpiolib API, also return NULL when    108 the rest of gpiolib API, also return NULL when gpiolib support is disabled.
107 This is helpful to driver authors, since they     109 This is helpful to driver authors, since they do not need to special case
108 -ENOSYS return codes.  System integrators shou    110 -ENOSYS return codes.  System integrators should however be careful to enable
109 gpiolib on systems that need it.                  111 gpiolib on systems that need it.
110                                                   112 
111 For a function using multiple GPIOs all of tho    113 For a function using multiple GPIOs all of those can be obtained with one call::
112                                                   114 
113         struct gpio_descs *gpiod_get_array(str    115         struct gpio_descs *gpiod_get_array(struct device *dev,
114                                            con    116                                            const char *con_id,
115                                            enu    117                                            enum gpiod_flags flags)
116                                                   118 
117 This function returns a struct gpio_descs whic    119 This function returns a struct gpio_descs which contains an array of
118 descriptors.  It also contains a pointer to a     120 descriptors.  It also contains a pointer to a gpiolib private structure which,
119 if passed back to get/set array functions, may    121 if passed back to get/set array functions, may speed up I/O processing::
120                                                   122 
121         struct gpio_descs {                       123         struct gpio_descs {
122                 struct gpio_array *info;          124                 struct gpio_array *info;
123                 unsigned int ndescs;              125                 unsigned int ndescs;
124                 struct gpio_desc *desc[];         126                 struct gpio_desc *desc[];
125         }                                         127         }
126                                                   128 
127 The following function returns NULL instead of    129 The following function returns NULL instead of -ENOENT if no GPIOs have been
128 assigned to the requested function::              130 assigned to the requested function::
129                                                   131 
130         struct gpio_descs *gpiod_get_array_opt    132         struct gpio_descs *gpiod_get_array_optional(struct device *dev,
131                                                   133                                                     const char *con_id,
132                                                   134                                                     enum gpiod_flags flags)
133                                                   135 
134 Device-managed variants of these functions are    136 Device-managed variants of these functions are also defined::
135                                                   137 
136         struct gpio_desc *devm_gpiod_get(struc    138         struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id,
137                                          enum     139                                          enum gpiod_flags flags)
138                                                   140 
139         struct gpio_desc *devm_gpiod_get_index    141         struct gpio_desc *devm_gpiod_get_index(struct device *dev,
140                                                   142                                                const char *con_id,
141                                                   143                                                unsigned int idx,
142                                                   144                                                enum gpiod_flags flags)
143                                                   145 
144         struct gpio_desc *devm_gpiod_get_optio    146         struct gpio_desc *devm_gpiod_get_optional(struct device *dev,
145                                                   147                                                   const char *con_id,
146                                                   148                                                   enum gpiod_flags flags)
147                                                   149 
148         struct gpio_desc *devm_gpiod_get_index    150         struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev,
149                                                   151                                                         const char *con_id,
150                                                   152                                                         unsigned int index,
151                                                   153                                                         enum gpiod_flags flags)
152                                                   154 
153         struct gpio_descs *devm_gpiod_get_arra    155         struct gpio_descs *devm_gpiod_get_array(struct device *dev,
154                                                   156                                                 const char *con_id,
155                                                   157                                                 enum gpiod_flags flags)
156                                                   158 
157         struct gpio_descs *devm_gpiod_get_arra    159         struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev,
158                                                   160                                                          const char *con_id,
159                                                   161                                                          enum gpiod_flags flags)
160                                                   162 
161 A GPIO descriptor can be disposed of using the    163 A GPIO descriptor can be disposed of using the gpiod_put() function::
162                                                   164 
163         void gpiod_put(struct gpio_desc *desc)    165         void gpiod_put(struct gpio_desc *desc)
164                                                   166 
165 For an array of GPIOs this function can be use    167 For an array of GPIOs this function can be used::
166                                                   168 
167         void gpiod_put_array(struct gpio_descs    169         void gpiod_put_array(struct gpio_descs *descs)
168                                                   170 
169 It is strictly forbidden to use a descriptor a    171 It is strictly forbidden to use a descriptor after calling these functions.
170 It is also not allowed to individually release    172 It is also not allowed to individually release descriptors (using gpiod_put())
171 from an array acquired with gpiod_get_array().    173 from an array acquired with gpiod_get_array().
172                                                   174 
173 The device-managed variants are, unsurprisingl    175 The device-managed variants are, unsurprisingly::
174                                                   176 
175         void devm_gpiod_put(struct device *dev    177         void devm_gpiod_put(struct device *dev, struct gpio_desc *desc)
176                                                   178 
177         void devm_gpiod_put_array(struct devic    179         void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs)
178                                                   180 
179                                                   181 
180 Using GPIOs                                       182 Using GPIOs
181 ===========                                       183 ===========
182                                                   184 
183 Setting Direction                                 185 Setting Direction
184 -----------------                                 186 -----------------
185 The first thing a driver must do with a GPIO i    187 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    188 direction-setting flags have been given to gpiod_get*(), this is done by
187 invoking one of the gpiod_direction_*() functi    189 invoking one of the gpiod_direction_*() functions::
188                                                   190 
189         int gpiod_direction_input(struct gpio_    191         int gpiod_direction_input(struct gpio_desc *desc)
190         int gpiod_direction_output(struct gpio    192         int gpiod_direction_output(struct gpio_desc *desc, int value)
191                                                   193 
192 The return value is zero for success, else a n    194 The return value is zero for success, else a negative errno. It should be
193 checked, since the get/set calls don't return     195 checked, since the get/set calls don't return errors and since misconfiguration
194 is possible. You should normally issue these c    196 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    197 for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part
196 of early board setup.                             198 of early board setup.
197                                                   199 
198 For output GPIOs, the value provided becomes t    200 For output GPIOs, the value provided becomes the initial output value. This
199 helps avoid signal glitching during system sta    201 helps avoid signal glitching during system startup.
200                                                   202 
201 A driver can also query the current direction     203 A driver can also query the current direction of a GPIO::
202                                                   204 
203         int gpiod_get_direction(const struct g    205         int gpiod_get_direction(const struct gpio_desc *desc)
204                                                   206 
205 This function returns 0 for output, 1 for inpu    207 This function returns 0 for output, 1 for input, or an error code in case of error.
206                                                   208 
207 Be aware that there is no default direction fo    209 Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO
208 without setting its direction first is illegal    210 without setting its direction first is illegal and will result in undefined
209 behavior!**                                       211 behavior!**
210                                                   212 
211                                                   213 
212 Spinlock-Safe GPIO Access                         214 Spinlock-Safe GPIO Access
213 -------------------------                         215 -------------------------
214 Most GPIO controllers can be accessed with mem    216 Most GPIO controllers can be accessed with memory read/write instructions. Those
215 don't need to sleep, and can safely be done fr    217 don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ
216 handlers and similar contexts.                    218 handlers and similar contexts.
217                                                   219 
218 Use the following calls to access GPIOs from a    220 Use the following calls to access GPIOs from an atomic context::
219                                                   221 
220         int gpiod_get_value(const struct gpio_    222         int gpiod_get_value(const struct gpio_desc *desc);
221         void gpiod_set_value(struct gpio_desc     223         void gpiod_set_value(struct gpio_desc *desc, int value);
222                                                   224 
223 The values are boolean, zero for inactive, non    225 The values are boolean, zero for inactive, nonzero for active. When reading the
224 value of an output pin, the value returned sho    226 value of an output pin, the value returned should be what's seen on the pin.
225 That won't always match the specified output v    227 That won't always match the specified output value, because of issues including
226 open-drain signaling and output latencies.        228 open-drain signaling and output latencies.
227                                                   229 
228 The get/set calls do not return errors because    230 The get/set calls do not return errors because "invalid GPIO" should have been
229 reported earlier from gpiod_direction_*(). How    231 reported earlier from gpiod_direction_*(). However, note that not all platforms
230 can read the value of output pins; those that     232 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    233 Also, using these calls for GPIOs that can't safely be accessed without sleeping
232 (see below) is an error.                          234 (see below) is an error.
233                                                   235 
234                                                   236 
235 GPIO Access That May Sleep                        237 GPIO Access That May Sleep
236 --------------------------                        238 --------------------------
237 Some GPIO controllers must be accessed using m    239 Some GPIO controllers must be accessed using message based buses like I2C or
238 SPI. Commands to read or write those GPIO valu    240 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     241 head of a queue to transmit a command and get its response. This requires
240 sleeping, which can't be done from inside IRQ     242 sleeping, which can't be done from inside IRQ handlers.
241                                                   243 
242 Platforms that support this type of GPIO disti    244 Platforms that support this type of GPIO distinguish them from other GPIOs by
243 returning nonzero from this call::                245 returning nonzero from this call::
244                                                   246 
245         int gpiod_cansleep(const struct gpio_d    247         int gpiod_cansleep(const struct gpio_desc *desc)
246                                                   248 
247 To access such GPIOs, a different set of acces    249 To access such GPIOs, a different set of accessors is defined::
248                                                   250 
249         int gpiod_get_value_cansleep(const str    251         int gpiod_get_value_cansleep(const struct gpio_desc *desc)
250         void gpiod_set_value_cansleep(struct g    252         void gpiod_set_value_cansleep(struct gpio_desc *desc, int value)
251                                                   253 
252 Accessing such GPIOs requires a context which     254 Accessing such GPIOs requires a context which may sleep, for example a threaded
253 IRQ handler, and those accessors must be used     255 IRQ handler, and those accessors must be used instead of spinlock-safe
254 accessors without the cansleep() name suffix.     256 accessors without the cansleep() name suffix.
255                                                   257 
256 Other than the fact that these accessors might    258 Other than the fact that these accessors might sleep, and will work on GPIOs
257 that can't be accessed from hardIRQ handlers,     259 that can't be accessed from hardIRQ handlers, these calls act the same as the
258 spinlock-safe calls.                              260 spinlock-safe calls.
259                                                   261 
260                                                   262 
261 .. _active_low_semantics:                         263 .. _active_low_semantics:
262                                                   264 
263 The active low and open drain semantics           265 The active low and open drain semantics
264 ---------------------------------------           266 ---------------------------------------
265 As a consumer should not have to care about th    267 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    268 gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with
267 the *logical* value. With this they take the a    269 the *logical* value. With this they take the active low property into account.
268 This means that they check whether the GPIO is    270 This means that they check whether the GPIO is configured to be active low,
269 and if so, they manipulate the passed value be    271 and if so, they manipulate the passed value before the physical line level is
270 driven.                                           272 driven.
271                                                   273 
272 The same is applicable for open drain or open     274 The same is applicable for open drain or open source output lines: those do not
273 actively drive their output high (open drain)     275 actively drive their output high (open drain) or low (open source), they just
274 switch their output to a high impedance value.    276 switch their output to a high impedance value. The consumer should not need to
275 care. (For details read about open drain in dr    277 care. (For details read about open drain in driver.rst.)
276                                                   278 
277 With this, all the gpiod_set_(array)_value_xxx    279 With this, all the gpiod_set_(array)_value_xxx() functions interpret the
278 parameter "value" as "active" ("1") or "inacti    280 parameter "value" as "active" ("1") or "inactive" ("0"). The physical line
279 level will be driven accordingly.                 281 level will be driven accordingly.
280                                                   282 
281 As an example, if the active low property for     283 As an example, if the active low property for a dedicated GPIO is set, and the
282 gpiod_set_(array)_value_xxx() passes "active"     284 gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level
283 will be driven low.                               285 will be driven low.
284                                                   286 
285 To summarize::                                    287 To summarize::
286                                                   288 
287   Function (example)                 line prop    289   Function (example)                 line property          physical line
288   gpiod_set_raw_value(desc, 0);      don't car    290   gpiod_set_raw_value(desc, 0);      don't care             low
289   gpiod_set_raw_value(desc, 1);      don't car    291   gpiod_set_raw_value(desc, 1);      don't care             high
290   gpiod_set_value(desc, 0);          default (    292   gpiod_set_value(desc, 0);          default (active high)  low
291   gpiod_set_value(desc, 1);          default (    293   gpiod_set_value(desc, 1);          default (active high)  high
292   gpiod_set_value(desc, 0);          active lo    294   gpiod_set_value(desc, 0);          active low             high
293   gpiod_set_value(desc, 1);          active lo    295   gpiod_set_value(desc, 1);          active low             low
294   gpiod_set_value(desc, 0);          open drai    296   gpiod_set_value(desc, 0);          open drain             low
295   gpiod_set_value(desc, 1);          open drai    297   gpiod_set_value(desc, 1);          open drain             high impedance
296   gpiod_set_value(desc, 0);          open sour    298   gpiod_set_value(desc, 0);          open source            high impedance
297   gpiod_set_value(desc, 1);          open sour    299   gpiod_set_value(desc, 1);          open source            high
298                                                   300 
299 It is possible to override these semantics usi    301 It is possible to override these semantics using the set_raw/get_raw functions
300 but it should be avoided as much as possible,     302 but it should be avoided as much as possible, especially by system-agnostic drivers
301 which should not need to care about the actual    303 which should not need to care about the actual physical line level and worry about
302 the logical value instead.                        304 the logical value instead.
303                                                   305 
304                                                   306 
305 Accessing raw GPIO values                         307 Accessing raw GPIO values
306 -------------------------                         308 -------------------------
307 Consumers exist that need to manage the logica    309 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     310 their device will actually receive, no matter what lies between it and the GPIO
309 line.                                             311 line.
310                                                   312 
311 The following set of calls ignore the active-l    313 The following set of calls ignore the active-low or open drain property of a GPIO and
312 work on the raw line value::                      314 work on the raw line value::
313                                                   315 
314         int gpiod_get_raw_value(const struct g    316         int gpiod_get_raw_value(const struct gpio_desc *desc)
315         void gpiod_set_raw_value(struct gpio_d    317         void gpiod_set_raw_value(struct gpio_desc *desc, int value)
316         int gpiod_get_raw_value_cansleep(const    318         int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc)
317         void gpiod_set_raw_value_cansleep(stru    319         void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value)
318         int gpiod_direction_output_raw(struct     320         int gpiod_direction_output_raw(struct gpio_desc *desc, int value)
319                                                   321 
320 The active low state of a GPIO can also be que    322 The active low state of a GPIO can also be queried and toggled using the
321 following calls::                                 323 following calls::
322                                                   324 
323         int gpiod_is_active_low(const struct g    325         int gpiod_is_active_low(const struct gpio_desc *desc)
324         void gpiod_toggle_active_low(struct gp    326         void gpiod_toggle_active_low(struct gpio_desc *desc)
325                                                   327 
326 Note that these functions should only be used     328 Note that these functions should only be used with great moderation; a driver
327 should not have to care about the physical lin    329 should not have to care about the physical line level or open drain semantics.
328                                                   330 
329                                                   331 
330 Access multiple GPIOs with a single function c    332 Access multiple GPIOs with a single function call
331 ----------------------------------------------    333 -------------------------------------------------
332 The following functions get or set the values     334 The following functions get or set the values of an array of GPIOs::
333                                                   335 
334         int gpiod_get_array_value(unsigned int    336         int gpiod_get_array_value(unsigned int array_size,
335                                   struct gpio_    337                                   struct gpio_desc **desc_array,
336                                   struct gpio_    338                                   struct gpio_array *array_info,
337                                   unsigned lon    339                                   unsigned long *value_bitmap);
338         int gpiod_get_raw_array_value(unsigned    340         int gpiod_get_raw_array_value(unsigned int array_size,
339                                       struct g    341                                       struct gpio_desc **desc_array,
340                                       struct g    342                                       struct gpio_array *array_info,
341                                       unsigned    343                                       unsigned long *value_bitmap);
342         int gpiod_get_array_value_cansleep(uns    344         int gpiod_get_array_value_cansleep(unsigned int array_size,
343                                            str    345                                            struct gpio_desc **desc_array,
344                                            str    346                                            struct gpio_array *array_info,
345                                            uns    347                                            unsigned long *value_bitmap);
346         int gpiod_get_raw_array_value_cansleep    348         int gpiod_get_raw_array_value_cansleep(unsigned int array_size,
347                                            str    349                                            struct gpio_desc **desc_array,
348                                            str    350                                            struct gpio_array *array_info,
349                                            uns    351                                            unsigned long *value_bitmap);
350                                                   352 
351         int gpiod_set_array_value(unsigned int    353         int gpiod_set_array_value(unsigned int array_size,
352                                   struct gpio_    354                                   struct gpio_desc **desc_array,
353                                   struct gpio_    355                                   struct gpio_array *array_info,
354                                   unsigned lon    356                                   unsigned long *value_bitmap)
355         int gpiod_set_raw_array_value(unsigned    357         int gpiod_set_raw_array_value(unsigned int array_size,
356                                       struct g    358                                       struct gpio_desc **desc_array,
357                                       struct g    359                                       struct gpio_array *array_info,
358                                       unsigned    360                                       unsigned long *value_bitmap)
359         int gpiod_set_array_value_cansleep(uns    361         int gpiod_set_array_value_cansleep(unsigned int array_size,
360                                            str    362                                            struct gpio_desc **desc_array,
361                                            str    363                                            struct gpio_array *array_info,
362                                            uns    364                                            unsigned long *value_bitmap)
363         int gpiod_set_raw_array_value_cansleep    365         int gpiod_set_raw_array_value_cansleep(unsigned int array_size,
364                                                   366                                                struct gpio_desc **desc_array,
365                                                   367                                                struct gpio_array *array_info,
366                                                   368                                                unsigned long *value_bitmap)
367                                                   369 
368 The array can be an arbitrary set of GPIOs. Th    370 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    371 GPIOs belonging to the same bank or chip simultaneously if supported by the
370 corresponding chip driver. In that case a sign    372 corresponding chip driver. In that case a significantly improved performance
371 can be expected. If simultaneous access is not    373 can be expected. If simultaneous access is not possible the GPIOs will be
372 accessed sequentially.                            374 accessed sequentially.
373                                                   375 
374 The functions take four arguments:                376 The functions take four arguments:
375                                                   377 
376         * array_size    - the number of array     378         * array_size    - the number of array elements
377         * desc_array    - an array of GPIO des    379         * desc_array    - an array of GPIO descriptors
378         * array_info    - optional information    380         * array_info    - optional information obtained from gpiod_get_array()
379         * value_bitmap  - a bitmap to store th    381         * value_bitmap  - a bitmap to store the GPIOs' values (get) or
380           a bitmap of values to assign to the     382           a bitmap of values to assign to the GPIOs (set)
381                                                   383 
382 The descriptor array can be obtained using the    384 The descriptor array can be obtained using the gpiod_get_array() function
383 or one of its variants. If the group of descri    385 or one of its variants. If the group of descriptors returned by that function
384 matches the desired group of GPIOs, those GPIO    386 matches the desired group of GPIOs, those GPIOs can be accessed by simply using
385 the struct gpio_descs returned by gpiod_get_ar    387 the struct gpio_descs returned by gpiod_get_array()::
386                                                   388 
387         struct gpio_descs *my_gpio_descs = gpi    389         struct gpio_descs *my_gpio_descs = gpiod_get_array(...);
388         gpiod_set_array_value(my_gpio_descs->n    390         gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc,
389                               my_gpio_descs->i    391                               my_gpio_descs->info, my_gpio_value_bitmap);
390                                                   392 
391 It is also possible to access a completely arb    393 It is also possible to access a completely arbitrary array of descriptors. The
392 descriptors may be obtained using any combinat    394 descriptors may be obtained using any combination of gpiod_get() and
393 gpiod_get_array(). Afterwards the array of des    395 gpiod_get_array(). Afterwards the array of descriptors has to be setup
394 manually before it can be passed to one of the    396 manually before it can be passed to one of the above functions.  In that case,
395 array_info should be set to NULL.                 397 array_info should be set to NULL.
396                                                   398 
397 Note that for optimal performance GPIOs belong    399 Note that for optimal performance GPIOs belonging to the same chip should be
398 contiguous within the array of descriptors.       400 contiguous within the array of descriptors.
399                                                   401 
400 Still better performance may be achieved if ar    402 Still better performance may be achieved if array indexes of the descriptors
401 match hardware pin numbers of a single chip.      403 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    404 array function matches the one obtained from gpiod_get_array() and array_info
403 associated with the array is also passed, the     405 associated with the array is also passed, the function may take a fast bitmap
404 processing path, passing the value_bitmap argu    406 processing path, passing the value_bitmap argument directly to the respective
405 .get/set_multiple() callback of the chip.  Tha    407 .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    408 banks as data I/O ports without much loss of performance.
407                                                   409 
408 The return value of gpiod_get_array_value() an    410 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    411 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    412 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    413 values are stored in value_array rather than passed back as return value.
412                                                   414 
413                                                   415 
414 GPIOs mapped to IRQs                              416 GPIOs mapped to IRQs
415 --------------------                              417 --------------------
416 GPIO lines can quite often be used as IRQs. Yo    418 GPIO lines can quite often be used as IRQs. You can get the IRQ number
417 corresponding to a given GPIO using the follow    419 corresponding to a given GPIO using the following call::
418                                                   420 
419         int gpiod_to_irq(const struct gpio_des    421         int gpiod_to_irq(const struct gpio_desc *desc)
420                                                   422 
421 It will return an IRQ number, or a negative er    423 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    424 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     425 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    426 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    427 from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep.
426                                                   428 
427 Non-error values returned from gpiod_to_irq()     429 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    430 free_irq(). They will often be stored into IRQ resources for platform devices,
429 by the board-specific initialization code. Not    431 by the board-specific initialization code. Note that IRQ trigger options are
430 part of the IRQ interface, e.g. IRQF_TRIGGER_F    432 part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup
431 capabilities.                                     433 capabilities.
432                                                   434 
433                                                   435 
434 GPIOs and ACPI                                    436 GPIOs and ACPI
435 ==============                                    437 ==============
436                                                   438 
437 On ACPI systems, GPIOs are described by GpioIo    439 On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by
438 the _CRS configuration objects of devices.  Th    440 the _CRS configuration objects of devices.  Those resources do not provide
439 connection IDs (names) for GPIOs, so it is nec    441 connection IDs (names) for GPIOs, so it is necessary to use an additional
440 mechanism for this purpose.                       442 mechanism for this purpose.
441                                                   443 
442 Systems compliant with ACPI 5.1 or newer may p    444 Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object
443 which, among other things, may be used to prov    445 which, among other things, may be used to provide connection IDs for specific
444 GPIOs described by the GpioIo()/GpioInt() reso    446 GPIOs described by the GpioIo()/GpioInt() resources in _CRS.  If that is the
445 case, it will be handled by the GPIO subsystem    447 case, it will be handled by the GPIO subsystem automatically.  However, if the
446 _DSD is not present, the mappings between Gpio    448 _DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO
447 connection IDs need to be provided by device d    449 connection IDs need to be provided by device drivers.
448                                                   450 
449 For details refer to Documentation/firmware-gu    451 For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst
450                                                   452 
451                                                   453 
452 Interacting With the Legacy GPIO Subsystem        454 Interacting With the Legacy GPIO Subsystem
453 ==========================================        455 ==========================================
454 Many kernel subsystems and drivers still handl    456 Many kernel subsystems and drivers still handle GPIOs using the legacy
455 integer-based interface. It is strongly recomm    457 integer-based interface. It is strongly recommended to update these to the new
456 gpiod interface. For cases where both interfac    458 gpiod interface. For cases where both interfaces need to be used, the following
457 two functions allow to convert a GPIO descript    459 two functions allow to convert a GPIO descriptor into the GPIO integer namespace
458 and vice-versa::                                  460 and vice-versa::
459                                                   461 
460         int desc_to_gpio(const struct gpio_des    462         int desc_to_gpio(const struct gpio_desc *desc)
461         struct gpio_desc *gpio_to_desc(unsigne    463         struct gpio_desc *gpio_to_desc(unsigned gpio)
462                                                   464 
463 The GPIO number returned by desc_to_gpio() can    465 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    466 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_    467 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    468 acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only
467 considered valid until that GPIO number is rel    469 considered valid until that GPIO number is released using gpio_free().
468                                                   470 
469 Freeing a GPIO obtained by one API with the ot    471 Freeing a GPIO obtained by one API with the other API is forbidden and an
470 unchecked error.                                  472 unchecked error.
                                                      

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