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 33All the functions that work with the descriptor-based GPIO interface are 34prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy 35interface. No other function in the kernel should use these prefixes. The use 36of the legacy functions is strongly discouraged, new code should use 37<linux/gpio/consumer.h> and descriptors exclusively. 38 39 40Obtaining and Disposing GPIOs 41============================= 42 43With the descriptor-based interface, GPIOs are identified with an opaque, 44non-forgeable handler that must be obtained through a call to one of the 45gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the 46device that will use the GPIO and the function the requested GPIO is supposed to 47fulfill:: 48 49 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id, 50 enum gpiod_flags flags) 51 52If a function is implemented by using several GPIOs together (e.g. a simple LED 53device that displays digits), an additional index argument can be specified:: 54 55 struct gpio_desc *gpiod_get_index(struct device *dev, 56 const char *con_id, unsigned int idx, 57 enum gpiod_flags flags) 58 59For a more detailed description of the con_id parameter in the DeviceTree case 60see Documentation/driver-api/gpio/board.rst 61 62The flags parameter is used to optionally specify a direction and initial value 63for the GPIO. Values can be: 64 65* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set 66 later with one of the dedicated functions. 67* GPIOD_IN to initialize the GPIO as input. 68* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0. 69* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1. 70* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line 71 to be electrically used with open drain. 72* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line 73 to be electrically used with open drain. 74 75Note that the initial value is *logical* and the physical line level depends on 76whether the line is configured active high or active low (see 77:ref:`active_low_semantics`). 78 79The two last flags are used for use cases where open drain is mandatory, such 80as I2C: if the line is not already configured as open drain in the mappings 81(see board.rst), then open drain will be enforced anyway and a warning will be 82printed that the board configuration needs to be updated to match the use case. 83 84Both functions return either a valid GPIO descriptor, or an error code checkable 85with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned 86if and only if no GPIO has been assigned to the device/function/index triplet, 87other error codes are used for cases where a GPIO has been assigned but an error 88occurred while trying to acquire it. This is useful to discriminate between mere 89errors and an absence of GPIO for optional GPIO parameters. For the common 90pattern where a GPIO is optional, the gpiod_get_optional() and 91gpiod_get_index_optional() functions can be used. These functions return NULL 92instead of -ENOENT if no GPIO has been assigned to the requested function:: 93 94 struct gpio_desc *gpiod_get_optional(struct device *dev, 95 const char *con_id, 96 enum gpiod_flags flags) 97 98 struct gpio_desc *gpiod_get_index_optional(struct device *dev, 99 const char *con_id, 100 unsigned int index, 101 enum gpiod_flags flags) 102 103Note that gpio_get*_optional() functions (and their managed variants), unlike 104the rest of gpiolib API, also return NULL when gpiolib support is disabled. 105This is helpful to driver authors, since they do not need to special case 106-ENOSYS return codes. System integrators should however be careful to enable 107gpiolib on systems that need it. 108 109For a function using multiple GPIOs all of those can be obtained with one call:: 110 111 struct gpio_descs *gpiod_get_array(struct device *dev, 112 const char *con_id, 113 enum gpiod_flags flags) 114 115This function returns a struct gpio_descs which contains an array of 116descriptors. It also contains a pointer to a gpiolib private structure which, 117if passed back to get/set array functions, may speed up I/O proocessing:: 118 119 struct gpio_descs { 120 struct gpio_array *info; 121 unsigned int ndescs; 122 struct gpio_desc *desc[]; 123 } 124 125The following function returns NULL instead of -ENOENT if no GPIOs have been 126assigned to the requested function:: 127 128 struct gpio_descs *gpiod_get_array_optional(struct device *dev, 129 const char *con_id, 130 enum gpiod_flags flags) 131 132Device-managed variants of these functions are also defined:: 133 134 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, 135 enum gpiod_flags flags) 136 137 struct gpio_desc *devm_gpiod_get_index(struct device *dev, 138 const char *con_id, 139 unsigned int idx, 140 enum gpiod_flags flags) 141 142 struct gpio_desc *devm_gpiod_get_optional(struct device *dev, 143 const char *con_id, 144 enum gpiod_flags flags) 145 146 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, 147 const char *con_id, 148 unsigned int index, 149 enum gpiod_flags flags) 150 151 struct gpio_descs *devm_gpiod_get_array(struct device *dev, 152 const char *con_id, 153 enum gpiod_flags flags) 154 155 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev, 156 const char *con_id, 157 enum gpiod_flags flags) 158 159A GPIO descriptor can be disposed of using the gpiod_put() function:: 160 161 void gpiod_put(struct gpio_desc *desc) 162 163For an array of GPIOs this function can be used:: 164 165 void gpiod_put_array(struct gpio_descs *descs) 166 167It is strictly forbidden to use a descriptor after calling these functions. 168It is also not allowed to individually release descriptors (using gpiod_put()) 169from an array acquired with gpiod_get_array(). 170 171The device-managed variants are, unsurprisingly:: 172 173 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) 174 175 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) 176 177 178Using GPIOs 179=========== 180 181Setting Direction 182----------------- 183The first thing a driver must do with a GPIO is setting its direction. If no 184direction-setting flags have been given to gpiod_get*(), this is done by 185invoking one of the gpiod_direction_*() functions:: 186 187 int gpiod_direction_input(struct gpio_desc *desc) 188 int gpiod_direction_output(struct gpio_desc *desc, int value) 189 190The return value is zero for success, else a negative errno. It should be 191checked, since the get/set calls don't return errors and since misconfiguration 192is possible. You should normally issue these calls from a task context. However, 193for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part 194of early board setup. 195 196For output GPIOs, the value provided becomes the initial output value. This 197helps avoid signal glitching during system startup. 198 199A driver can also query the current direction of a GPIO:: 200 201 int gpiod_get_direction(const struct gpio_desc *desc) 202 203This function returns 0 for output, 1 for input, or an error code in case of error. 204 205Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO 206without setting its direction first is illegal and will result in undefined 207behavior!** 208 209 210Spinlock-Safe GPIO Access 211------------------------- 212Most GPIO controllers can be accessed with memory read/write instructions. Those 213don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ 214handlers and similar contexts. 215 216Use the following calls to access GPIOs from an atomic context:: 217 218 int gpiod_get_value(const struct gpio_desc *desc); 219 void gpiod_set_value(struct gpio_desc *desc, int value); 220 221The values are boolean, zero for low, nonzero for high. When reading the value 222of an output pin, the value returned should be what's seen on the pin. That 223won't always match the specified output value, because of issues including 224open-drain signaling and output latencies. 225 226The get/set calls do not return errors because "invalid GPIO" should have been 227reported earlier from gpiod_direction_*(). However, note that not all platforms 228can read the value of output pins; those that can't should always return zero. 229Also, using these calls for GPIOs that can't safely be accessed without sleeping 230(see below) is an error. 231 232 233GPIO Access That May Sleep 234-------------------------- 235Some GPIO controllers must be accessed using message based buses like I2C or 236SPI. Commands to read or write those GPIO values require waiting to get to the 237head of a queue to transmit a command and get its response. This requires 238sleeping, which can't be done from inside IRQ handlers. 239 240Platforms that support this type of GPIO distinguish them from other GPIOs by 241returning nonzero from this call:: 242 243 int gpiod_cansleep(const struct gpio_desc *desc) 244 245To access such GPIOs, a different set of accessors is defined:: 246 247 int gpiod_get_value_cansleep(const struct gpio_desc *desc) 248 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value) 249 250Accessing such GPIOs requires a context which may sleep, for example a threaded 251IRQ handler, and those accessors must be used instead of spinlock-safe 252accessors without the cansleep() name suffix. 253 254Other than the fact that these accessors might sleep, and will work on GPIOs 255that can't be accessed from hardIRQ handlers, these calls act the same as the 256spinlock-safe calls. 257 258 259.. _active_low_semantics: 260 261The active low and open drain semantics 262--------------------------------------- 263As a consumer should not have to care about the physical line level, all of the 264gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with 265the *logical* value. With this they take the active low property into account. 266This means that they check whether the GPIO is configured to be active low, 267and if so, they manipulate the passed value before the physical line level is 268driven. 269 270The same is applicable for open drain or open source output lines: those do not 271actively drive their output high (open drain) or low (open source), they just 272switch their output to a high impedance value. The consumer should not need to 273care. (For details read about open drain in driver.rst.) 274 275With this, all the gpiod_set_(array)_value_xxx() functions interpret the 276parameter "value" as "asserted" ("1") or "de-asserted" ("0"). The physical line 277level will be driven accordingly. 278 279As an example, if the active low property for a dedicated GPIO is set, and the 280gpiod_set_(array)_value_xxx() passes "asserted" ("1"), the physical line level 281will be driven low. 282 283To summarize:: 284 285 Function (example) line property physical line 286 gpiod_set_raw_value(desc, 0); don't care low 287 gpiod_set_raw_value(desc, 1); don't care high 288 gpiod_set_value(desc, 0); default (active high) low 289 gpiod_set_value(desc, 1); default (active high) high 290 gpiod_set_value(desc, 0); active low high 291 gpiod_set_value(desc, 1); active low low 292 gpiod_set_value(desc, 0); open drain low 293 gpiod_set_value(desc, 1); open drain high impedance 294 gpiod_set_value(desc, 0); open source high impedance 295 gpiod_set_value(desc, 1); open source high 296 297It is possible to override these semantics using the set_raw/get_raw functions 298but it should be avoided as much as possible, especially by system-agnostic drivers 299which should not need to care about the actual physical line level and worry about 300the logical value instead. 301 302 303Accessing raw GPIO values 304------------------------- 305Consumers exist that need to manage the logical state of a GPIO line, i.e. the value 306their device will actually receive, no matter what lies between it and the GPIO 307line. 308 309The following set of calls ignore the active-low or open drain property of a GPIO and 310work on the raw line value:: 311 312 int gpiod_get_raw_value(const struct gpio_desc *desc) 313 void gpiod_set_raw_value(struct gpio_desc *desc, int value) 314 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc) 315 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) 316 int gpiod_direction_output_raw(struct gpio_desc *desc, int value) 317 318The active low state of a GPIO can also be queried and toggled using the 319following calls:: 320 321 int gpiod_is_active_low(const struct gpio_desc *desc) 322 void gpiod_toggle_active_low(struct gpio_desc *desc) 323 324Note that these functions should only be used with great moderation; a driver 325should not have to care about the physical line level or open drain semantics. 326 327 328Access multiple GPIOs with a single function call 329------------------------------------------------- 330The following functions get or set the values of an array of GPIOs:: 331 332 int gpiod_get_array_value(unsigned int array_size, 333 struct gpio_desc **desc_array, 334 struct gpio_array *array_info, 335 unsigned long *value_bitmap); 336 int gpiod_get_raw_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_array_value_cansleep(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_raw_array_value_cansleep(unsigned int array_size, 345 struct gpio_desc **desc_array, 346 struct gpio_array *array_info, 347 unsigned long *value_bitmap); 348 349 int gpiod_set_array_value(unsigned int array_size, 350 struct gpio_desc **desc_array, 351 struct gpio_array *array_info, 352 unsigned long *value_bitmap) 353 int gpiod_set_raw_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_array_value_cansleep(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_raw_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 366The array can be an arbitrary set of GPIOs. The functions will try to access 367GPIOs belonging to the same bank or chip simultaneously if supported by the 368corresponding chip driver. In that case a significantly improved performance 369can be expected. If simultaneous access is not possible the GPIOs will be 370accessed sequentially. 371 372The functions take four arguments: 373 374 * array_size - the number of array elements 375 * desc_array - an array of GPIO descriptors 376 * array_info - optional information obtained from gpiod_get_array() 377 * value_bitmap - a bitmap to store the GPIOs' values (get) or 378 a bitmap of values to assign to the GPIOs (set) 379 380The descriptor array can be obtained using the gpiod_get_array() function 381or one of its variants. If the group of descriptors returned by that function 382matches the desired group of GPIOs, those GPIOs can be accessed by simply using 383the struct gpio_descs returned by gpiod_get_array():: 384 385 struct gpio_descs *my_gpio_descs = gpiod_get_array(...); 386 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, 387 my_gpio_descs->info, my_gpio_value_bitmap); 388 389It is also possible to access a completely arbitrary array of descriptors. The 390descriptors may be obtained using any combination of gpiod_get() and 391gpiod_get_array(). Afterwards the array of descriptors has to be setup 392manually before it can be passed to one of the above functions. In that case, 393array_info should be set to NULL. 394 395Note that for optimal performance GPIOs belonging to the same chip should be 396contiguous within the array of descriptors. 397 398Still better performance may be achieved if array indexes of the descriptors 399match hardware pin numbers of a single chip. If an array passed to a get/set 400array function matches the one obtained from gpiod_get_array() and array_info 401associated with the array is also passed, the function may take a fast bitmap 402processing path, passing the value_bitmap argument directly to the respective 403.get/set_multiple() callback of the chip. That allows for utilization of GPIO 404banks as data I/O ports without much loss of performance. 405 406The return value of gpiod_get_array_value() and its variants is 0 on success 407or negative on error. Note the difference to gpiod_get_value(), which returns 4080 or 1 on success to convey the GPIO value. With the array functions, the GPIO 409values are stored in value_array rather than passed back as return value. 410 411 412GPIOs mapped to IRQs 413-------------------- 414GPIO lines can quite often be used as IRQs. You can get the IRQ number 415corresponding to a given GPIO using the following call:: 416 417 int gpiod_to_irq(const struct gpio_desc *desc) 418 419It will return an IRQ number, or a negative errno code if the mapping can't be 420done (most likely because that particular GPIO cannot be used as IRQ). It is an 421unchecked error to use a GPIO that wasn't set up as an input using 422gpiod_direction_input(), or to use an IRQ number that didn't originally come 423from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. 424 425Non-error values returned from gpiod_to_irq() can be passed to request_irq() or 426free_irq(). They will often be stored into IRQ resources for platform devices, 427by the board-specific initialization code. Note that IRQ trigger options are 428part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup 429capabilities. 430 431 432GPIOs and ACPI 433============== 434 435On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by 436the _CRS configuration objects of devices. Those resources do not provide 437connection IDs (names) for GPIOs, so it is necessary to use an additional 438mechanism for this purpose. 439 440Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object 441which, among other things, may be used to provide connection IDs for specific 442GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the 443case, it will be handled by the GPIO subsystem automatically. However, if the 444_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO 445connection IDs need to be provided by device drivers. 446 447For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst 448 449 450Interacting With the Legacy GPIO Subsystem 451========================================== 452Many kernel subsystems and drivers still handle GPIOs using the legacy 453integer-based interface. It is strongly recommended to update these to the new 454gpiod interface. For cases where both interfaces need to be used, the following 455two functions allow to convert a GPIO descriptor into the GPIO integer namespace 456and vice-versa:: 457 458 int desc_to_gpio(const struct gpio_desc *desc) 459 struct gpio_desc *gpio_to_desc(unsigned gpio) 460 461The GPIO number returned by desc_to_gpio() can safely be used as a parameter of 462the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed. 463All the same, a GPIO number passed to gpio_to_desc() must first be properly 464acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only 465considered valid until that GPIO number is released using gpio_free(). 466 467Freeing a GPIO obtained by one API with the other API is forbidden and an 468unchecked error. 469