1================================== 2GPIO Descriptor Consumer Interface 3================================== 4 5This document describes the consumer interface of the GPIO framework. Note that 6it describes the new descriptor-based interface. For a description of the 7deprecated integer-based GPIO interface please refer to legacy.rst. 8 9 10Guidelines for GPIOs consumers 11============================== 12 13Drivers that can't work without standard GPIO calls should have Kconfig entries 14that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to 15obtain and use GPIOs are available by including the following file:: 16 17 #include <linux/gpio/consumer.h> 18 19There are static inline stubs for all functions in the header file in the case 20where GPIOLIB is disabled. When these stubs are called they will emit 21warnings. These stubs are used for two use cases: 22 23- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that 24 the current platform does not enable or select GPIOLIB because we are not 25 going to execute the system anyway. 26 27- Truly optional GPIOLIB support - where the driver does not really make use 28 of the GPIOs on certain compile-time configurations for certain systems, but 29 will use it under other compile-time configurations. In this case the 30 consumer must make sure not to call into these functions, or the user will 31 be met with console warnings that may be perceived as intimidating. 32 Combining truly optional GPIOLIB usage with calls to 33 ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird 34 error messages. Use the ordinary getter functions with optional GPIOLIB: 35 some open coding of error handling should be expected when you do this. 36 37All the functions that work with the descriptor-based GPIO interface are 38prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy 39interface. No other function in the kernel should use these prefixes. The use 40of the legacy functions is strongly discouraged, new code should use 41<linux/gpio/consumer.h> and descriptors exclusively. 42 43 44Obtaining and Disposing GPIOs 45============================= 46 47With the descriptor-based interface, GPIOs are identified with an opaque, 48non-forgeable handler that must be obtained through a call to one of the 49gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the 50device that will use the GPIO and the function the requested GPIO is supposed to 51fulfill:: 52 53 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id, 54 enum gpiod_flags flags) 55 56If a function is implemented by using several GPIOs together (e.g. a simple LED 57device that displays digits), an additional index argument can be specified:: 58 59 struct gpio_desc *gpiod_get_index(struct device *dev, 60 const char *con_id, unsigned int idx, 61 enum gpiod_flags flags) 62 63For a more detailed description of the con_id parameter in the DeviceTree case 64see Documentation/driver-api/gpio/board.rst 65 66The flags parameter is used to optionally specify a direction and initial value 67for the GPIO. Values can be: 68 69* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set 70 later with one of the dedicated functions. 71* GPIOD_IN to initialize the GPIO as input. 72* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0. 73* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1. 74* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line 75 to be electrically used with open drain. 76* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line 77 to be electrically used with open drain. 78 79Note that the initial value is *logical* and the physical line level depends on 80whether the line is configured active high or active low (see 81:ref:`active_low_semantics`). 82 83The two last flags are used for use cases where open drain is mandatory, such 84as I2C: if the line is not already configured as open drain in the mappings 85(see board.rst), then open drain will be enforced anyway and a warning will be 86printed that the board configuration needs to be updated to match the use case. 87 88Both functions return either a valid GPIO descriptor, or an error code checkable 89with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned 90if and only if no GPIO has been assigned to the device/function/index triplet, 91other error codes are used for cases where a GPIO has been assigned but an error 92occurred while trying to acquire it. This is useful to discriminate between mere 93errors and an absence of GPIO for optional GPIO parameters. For the common 94pattern where a GPIO is optional, the gpiod_get_optional() and 95gpiod_get_index_optional() functions can be used. These functions return NULL 96instead of -ENOENT if no GPIO has been assigned to the requested function:: 97 98 struct gpio_desc *gpiod_get_optional(struct device *dev, 99 const char *con_id, 100 enum gpiod_flags flags) 101 102 struct gpio_desc *gpiod_get_index_optional(struct device *dev, 103 const char *con_id, 104 unsigned int index, 105 enum gpiod_flags flags) 106 107Note that gpio_get*_optional() functions (and their managed variants), unlike 108the rest of gpiolib API, also return NULL when gpiolib support is disabled. 109This is helpful to driver authors, since they do not need to special case 110-ENOSYS return codes. System integrators should however be careful to enable 111gpiolib on systems that need it. 112 113For a function using multiple GPIOs all of those can be obtained with one call:: 114 115 struct gpio_descs *gpiod_get_array(struct device *dev, 116 const char *con_id, 117 enum gpiod_flags flags) 118 119This function returns a struct gpio_descs which contains an array of 120descriptors. It also contains a pointer to a gpiolib private structure which, 121if passed back to get/set array functions, may speed up I/O processing:: 122 123 struct gpio_descs { 124 struct gpio_array *info; 125 unsigned int ndescs; 126 struct gpio_desc *desc[]; 127 } 128 129The following function returns NULL instead of -ENOENT if no GPIOs have been 130assigned to the requested function:: 131 132 struct gpio_descs *gpiod_get_array_optional(struct device *dev, 133 const char *con_id, 134 enum gpiod_flags flags) 135 136Device-managed variants of these functions are also defined:: 137 138 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, 139 enum gpiod_flags flags) 140 141 struct gpio_desc *devm_gpiod_get_index(struct device *dev, 142 const char *con_id, 143 unsigned int idx, 144 enum gpiod_flags flags) 145 146 struct gpio_desc *devm_gpiod_get_optional(struct device *dev, 147 const char *con_id, 148 enum gpiod_flags flags) 149 150 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, 151 const char *con_id, 152 unsigned int index, 153 enum gpiod_flags flags) 154 155 struct gpio_descs *devm_gpiod_get_array(struct device *dev, 156 const char *con_id, 157 enum gpiod_flags flags) 158 159 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev, 160 const char *con_id, 161 enum gpiod_flags flags) 162 163A GPIO descriptor can be disposed of using the gpiod_put() function:: 164 165 void gpiod_put(struct gpio_desc *desc) 166 167For an array of GPIOs this function can be used:: 168 169 void gpiod_put_array(struct gpio_descs *descs) 170 171It is strictly forbidden to use a descriptor after calling these functions. 172It is also not allowed to individually release descriptors (using gpiod_put()) 173from an array acquired with gpiod_get_array(). 174 175The device-managed variants are, unsurprisingly:: 176 177 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) 178 179 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) 180 181 182Using GPIOs 183=========== 184 185Setting Direction 186----------------- 187The first thing a driver must do with a GPIO is setting its direction. If no 188direction-setting flags have been given to gpiod_get*(), this is done by 189invoking one of the gpiod_direction_*() functions:: 190 191 int gpiod_direction_input(struct gpio_desc *desc) 192 int gpiod_direction_output(struct gpio_desc *desc, int value) 193 194The return value is zero for success, else a negative errno. It should be 195checked, since the get/set calls don't return errors and since misconfiguration 196is possible. You should normally issue these calls from a task context. However, 197for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part 198of early board setup. 199 200For output GPIOs, the value provided becomes the initial output value. This 201helps avoid signal glitching during system startup. 202 203A driver can also query the current direction of a GPIO:: 204 205 int gpiod_get_direction(const struct gpio_desc *desc) 206 207This function returns 0 for output, 1 for input, or an error code in case of error. 208 209Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO 210without setting its direction first is illegal and will result in undefined 211behavior!** 212 213 214Spinlock-Safe GPIO Access 215------------------------- 216Most GPIO controllers can be accessed with memory read/write instructions. Those 217don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ 218handlers and similar contexts. 219 220Use the following calls to access GPIOs from an atomic context:: 221 222 int gpiod_get_value(const struct gpio_desc *desc); 223 void gpiod_set_value(struct gpio_desc *desc, int value); 224 225The values are boolean, zero for inactive, nonzero for active. When reading the 226value of an output pin, the value returned should be what's seen on the pin. 227That won't always match the specified output value, because of issues including 228open-drain signaling and output latencies. 229 230The get/set calls do not return errors because "invalid GPIO" should have been 231reported earlier from gpiod_direction_*(). However, note that not all platforms 232can read the value of output pins; those that can't should always return zero. 233Also, using these calls for GPIOs that can't safely be accessed without sleeping 234(see below) is an error. 235 236 237GPIO Access That May Sleep 238-------------------------- 239Some GPIO controllers must be accessed using message based buses like I2C or 240SPI. Commands to read or write those GPIO values require waiting to get to the 241head of a queue to transmit a command and get its response. This requires 242sleeping, which can't be done from inside IRQ handlers. 243 244Platforms that support this type of GPIO distinguish them from other GPIOs by 245returning nonzero from this call:: 246 247 int gpiod_cansleep(const struct gpio_desc *desc) 248 249To access such GPIOs, a different set of accessors is defined:: 250 251 int gpiod_get_value_cansleep(const struct gpio_desc *desc) 252 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value) 253 254Accessing such GPIOs requires a context which may sleep, for example a threaded 255IRQ handler, and those accessors must be used instead of spinlock-safe 256accessors without the cansleep() name suffix. 257 258Other than the fact that these accessors might sleep, and will work on GPIOs 259that can't be accessed from hardIRQ handlers, these calls act the same as the 260spinlock-safe calls. 261 262 263.. _active_low_semantics: 264 265The active low and open drain semantics 266--------------------------------------- 267As a consumer should not have to care about the physical line level, all of the 268gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with 269the *logical* value. With this they take the active low property into account. 270This means that they check whether the GPIO is configured to be active low, 271and if so, they manipulate the passed value before the physical line level is 272driven. 273 274The same is applicable for open drain or open source output lines: those do not 275actively drive their output high (open drain) or low (open source), they just 276switch their output to a high impedance value. The consumer should not need to 277care. (For details read about open drain in driver.rst.) 278 279With this, all the gpiod_set_(array)_value_xxx() functions interpret the 280parameter "value" as "active" ("1") or "inactive" ("0"). The physical line 281level will be driven accordingly. 282 283As an example, if the active low property for a dedicated GPIO is set, and the 284gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level 285will be driven low. 286 287To summarize:: 288 289 Function (example) line property physical line 290 gpiod_set_raw_value(desc, 0); don't care low 291 gpiod_set_raw_value(desc, 1); don't care high 292 gpiod_set_value(desc, 0); default (active high) low 293 gpiod_set_value(desc, 1); default (active high) high 294 gpiod_set_value(desc, 0); active low high 295 gpiod_set_value(desc, 1); active low low 296 gpiod_set_value(desc, 0); open drain low 297 gpiod_set_value(desc, 1); open drain high impedance 298 gpiod_set_value(desc, 0); open source high impedance 299 gpiod_set_value(desc, 1); open source high 300 301It is possible to override these semantics using the set_raw/get_raw functions 302but it should be avoided as much as possible, especially by system-agnostic drivers 303which should not need to care about the actual physical line level and worry about 304the logical value instead. 305 306 307Accessing raw GPIO values 308------------------------- 309Consumers exist that need to manage the logical state of a GPIO line, i.e. the value 310their device will actually receive, no matter what lies between it and the GPIO 311line. 312 313The following set of calls ignore the active-low or open drain property of a GPIO and 314work on the raw line value:: 315 316 int gpiod_get_raw_value(const struct gpio_desc *desc) 317 void gpiod_set_raw_value(struct gpio_desc *desc, int value) 318 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc) 319 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) 320 int gpiod_direction_output_raw(struct gpio_desc *desc, int value) 321 322The active low state of a GPIO can also be queried and toggled using the 323following calls:: 324 325 int gpiod_is_active_low(const struct gpio_desc *desc) 326 void gpiod_toggle_active_low(struct gpio_desc *desc) 327 328Note that these functions should only be used with great moderation; a driver 329should not have to care about the physical line level or open drain semantics. 330 331 332Access multiple GPIOs with a single function call 333------------------------------------------------- 334The following functions get or set the values of an array of GPIOs:: 335 336 int gpiod_get_array_value(unsigned int array_size, 337 struct gpio_desc **desc_array, 338 struct gpio_array *array_info, 339 unsigned long *value_bitmap); 340 int gpiod_get_raw_array_value(unsigned int array_size, 341 struct gpio_desc **desc_array, 342 struct gpio_array *array_info, 343 unsigned long *value_bitmap); 344 int gpiod_get_array_value_cansleep(unsigned int array_size, 345 struct gpio_desc **desc_array, 346 struct gpio_array *array_info, 347 unsigned long *value_bitmap); 348 int gpiod_get_raw_array_value_cansleep(unsigned int array_size, 349 struct gpio_desc **desc_array, 350 struct gpio_array *array_info, 351 unsigned long *value_bitmap); 352 353 int gpiod_set_array_value(unsigned int array_size, 354 struct gpio_desc **desc_array, 355 struct gpio_array *array_info, 356 unsigned long *value_bitmap) 357 int gpiod_set_raw_array_value(unsigned int array_size, 358 struct gpio_desc **desc_array, 359 struct gpio_array *array_info, 360 unsigned long *value_bitmap) 361 int gpiod_set_array_value_cansleep(unsigned int array_size, 362 struct gpio_desc **desc_array, 363 struct gpio_array *array_info, 364 unsigned long *value_bitmap) 365 int gpiod_set_raw_array_value_cansleep(unsigned int array_size, 366 struct gpio_desc **desc_array, 367 struct gpio_array *array_info, 368 unsigned long *value_bitmap) 369 370The array can be an arbitrary set of GPIOs. The functions will try to access 371GPIOs belonging to the same bank or chip simultaneously if supported by the 372corresponding chip driver. In that case a significantly improved performance 373can be expected. If simultaneous access is not possible the GPIOs will be 374accessed sequentially. 375 376The functions take four arguments: 377 378 * array_size - the number of array elements 379 * desc_array - an array of GPIO descriptors 380 * array_info - optional information obtained from gpiod_get_array() 381 * value_bitmap - a bitmap to store the GPIOs' values (get) or 382 a bitmap of values to assign to the GPIOs (set) 383 384The descriptor array can be obtained using the gpiod_get_array() function 385or one of its variants. If the group of descriptors returned by that function 386matches the desired group of GPIOs, those GPIOs can be accessed by simply using 387the struct gpio_descs returned by gpiod_get_array():: 388 389 struct gpio_descs *my_gpio_descs = gpiod_get_array(...); 390 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, 391 my_gpio_descs->info, my_gpio_value_bitmap); 392 393It is also possible to access a completely arbitrary array of descriptors. The 394descriptors may be obtained using any combination of gpiod_get() and 395gpiod_get_array(). Afterwards the array of descriptors has to be setup 396manually before it can be passed to one of the above functions. In that case, 397array_info should be set to NULL. 398 399Note that for optimal performance GPIOs belonging to the same chip should be 400contiguous within the array of descriptors. 401 402Still better performance may be achieved if array indexes of the descriptors 403match hardware pin numbers of a single chip. If an array passed to a get/set 404array function matches the one obtained from gpiod_get_array() and array_info 405associated with the array is also passed, the function may take a fast bitmap 406processing path, passing the value_bitmap argument directly to the respective 407.get/set_multiple() callback of the chip. That allows for utilization of GPIO 408banks as data I/O ports without much loss of performance. 409 410The return value of gpiod_get_array_value() and its variants is 0 on success 411or negative on error. Note the difference to gpiod_get_value(), which returns 4120 or 1 on success to convey the GPIO value. With the array functions, the GPIO 413values are stored in value_array rather than passed back as return value. 414 415 416GPIOs mapped to IRQs 417-------------------- 418GPIO lines can quite often be used as IRQs. You can get the IRQ number 419corresponding to a given GPIO using the following call:: 420 421 int gpiod_to_irq(const struct gpio_desc *desc) 422 423It will return an IRQ number, or a negative errno code if the mapping can't be 424done (most likely because that particular GPIO cannot be used as IRQ). It is an 425unchecked error to use a GPIO that wasn't set up as an input using 426gpiod_direction_input(), or to use an IRQ number that didn't originally come 427from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. 428 429Non-error values returned from gpiod_to_irq() can be passed to request_irq() or 430free_irq(). They will often be stored into IRQ resources for platform devices, 431by the board-specific initialization code. Note that IRQ trigger options are 432part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup 433capabilities. 434 435 436GPIOs and ACPI 437============== 438 439On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by 440the _CRS configuration objects of devices. Those resources do not provide 441connection IDs (names) for GPIOs, so it is necessary to use an additional 442mechanism for this purpose. 443 444Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object 445which, among other things, may be used to provide connection IDs for specific 446GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the 447case, it will be handled by the GPIO subsystem automatically. However, if the 448_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO 449connection IDs need to be provided by device drivers. 450 451For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst 452 453 454Interacting With the Legacy GPIO Subsystem 455========================================== 456Many kernel subsystems and drivers still handle GPIOs using the legacy 457integer-based interface. It is strongly recommended to update these to the new 458gpiod interface. For cases where both interfaces need to be used, the following 459two functions allow to convert a GPIO descriptor into the GPIO integer namespace 460and vice-versa:: 461 462 int desc_to_gpio(const struct gpio_desc *desc) 463 struct gpio_desc *gpio_to_desc(unsigned gpio) 464 465The GPIO number returned by desc_to_gpio() can safely be used as a parameter of 466the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed. 467All the same, a GPIO number passed to gpio_to_desc() must first be properly 468acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only 469considered valid until that GPIO number is released using gpio_free(). 470 471Freeing a GPIO obtained by one API with the other API is forbidden and an 472unchecked error. 473