1================================== 2GPIO Descriptor Consumer Interface 3================================== 4 5This document describes the consumer interface of the GPIO framework. 6 7 8Guidelines for GPIOs consumers 9============================== 10 11Drivers that can't work without standard GPIO calls should have Kconfig entries 12that depend on GPIOLIB or select GPIOLIB. The functions that allow a driver to 13obtain and use GPIOs are available by including the following file:: 14 15 #include <linux/gpio/consumer.h> 16 17There are static inline stubs for all functions in the header file in the case 18where GPIOLIB is disabled. When these stubs are called they will emit 19warnings. These stubs are used for two use cases: 20 21- Simple compile coverage with e.g. COMPILE_TEST - it does not matter that 22 the current platform does not enable or select GPIOLIB because we are not 23 going to execute the system anyway. 24 25- Truly optional GPIOLIB support - where the driver does not really make use 26 of the GPIOs on certain compile-time configurations for certain systems, but 27 will use it under other compile-time configurations. In this case the 28 consumer must make sure not to call into these functions, or the user will 29 be met with console warnings that may be perceived as intimidating. 30 Combining truly optional GPIOLIB usage with calls to 31 ``[devm_]gpiod_get_optional()`` is a *bad idea*, and will result in weird 32 error messages. Use the ordinary getter functions with optional GPIOLIB: 33 some open coding of error handling should be expected when you do this. 34 35All the functions that work with the descriptor-based GPIO interface are 36prefixed with ``gpiod_``. The ``gpio_`` prefix is used for the legacy 37interface. No other function in the kernel should use these prefixes. The use 38of the legacy functions is strongly discouraged, new code should use 39<linux/gpio/consumer.h> and descriptors exclusively. 40 41 42Obtaining and Disposing GPIOs 43============================= 44 45With the descriptor-based interface, GPIOs are identified with an opaque, 46non-forgeable handler that must be obtained through a call to one of the 47gpiod_get() functions. Like many other kernel subsystems, gpiod_get() takes the 48device that will use the GPIO and the function the requested GPIO is supposed to 49fulfill:: 50 51 struct gpio_desc *gpiod_get(struct device *dev, const char *con_id, 52 enum gpiod_flags flags) 53 54If a function is implemented by using several GPIOs together (e.g. a simple LED 55device that displays digits), an additional index argument can be specified:: 56 57 struct gpio_desc *gpiod_get_index(struct device *dev, 58 const char *con_id, unsigned int idx, 59 enum gpiod_flags flags) 60 61For a more detailed description of the con_id parameter in the DeviceTree case 62see Documentation/driver-api/gpio/board.rst 63 64The flags parameter is used to optionally specify a direction and initial value 65for the GPIO. Values can be: 66 67* GPIOD_ASIS or 0 to not initialize the GPIO at all. The direction must be set 68 later with one of the dedicated functions. 69* GPIOD_IN to initialize the GPIO as input. 70* GPIOD_OUT_LOW to initialize the GPIO as output with a value of 0. 71* GPIOD_OUT_HIGH to initialize the GPIO as output with a value of 1. 72* GPIOD_OUT_LOW_OPEN_DRAIN same as GPIOD_OUT_LOW but also enforce the line 73 to be electrically used with open drain. 74* GPIOD_OUT_HIGH_OPEN_DRAIN same as GPIOD_OUT_HIGH but also enforce the line 75 to be electrically used with open drain. 76 77Note that the initial value is *logical* and the physical line level depends on 78whether the line is configured active high or active low (see 79:ref:`active_low_semantics`). 80 81The two last flags are used for use cases where open drain is mandatory, such 82as I2C: if the line is not already configured as open drain in the mappings 83(see board.rst), then open drain will be enforced anyway and a warning will be 84printed that the board configuration needs to be updated to match the use case. 85 86Both functions return either a valid GPIO descriptor, or an error code checkable 87with IS_ERR() (they will never return a NULL pointer). -ENOENT will be returned 88if and only if no GPIO has been assigned to the device/function/index triplet, 89other error codes are used for cases where a GPIO has been assigned but an error 90occurred while trying to acquire it. This is useful to discriminate between mere 91errors and an absence of GPIO for optional GPIO parameters. For the common 92pattern where a GPIO is optional, the gpiod_get_optional() and 93gpiod_get_index_optional() functions can be used. These functions return NULL 94instead of -ENOENT if no GPIO has been assigned to the requested function:: 95 96 struct gpio_desc *gpiod_get_optional(struct device *dev, 97 const char *con_id, 98 enum gpiod_flags flags) 99 100 struct gpio_desc *gpiod_get_index_optional(struct device *dev, 101 const char *con_id, 102 unsigned int index, 103 enum gpiod_flags flags) 104 105Note that gpio_get*_optional() functions (and their managed variants), unlike 106the rest of gpiolib API, also return NULL when gpiolib support is disabled. 107This is helpful to driver authors, since they do not need to special case 108-ENOSYS return codes. System integrators should however be careful to enable 109gpiolib on systems that need it. 110 111For a function using multiple GPIOs all of those can be obtained with one call:: 112 113 struct gpio_descs *gpiod_get_array(struct device *dev, 114 const char *con_id, 115 enum gpiod_flags flags) 116 117This function returns a struct gpio_descs which contains an array of 118descriptors. It also contains a pointer to a gpiolib private structure which, 119if passed back to get/set array functions, may speed up I/O processing:: 120 121 struct gpio_descs { 122 struct gpio_array *info; 123 unsigned int ndescs; 124 struct gpio_desc *desc[]; 125 } 126 127The following function returns NULL instead of -ENOENT if no GPIOs have been 128assigned to the requested function:: 129 130 struct gpio_descs *gpiod_get_array_optional(struct device *dev, 131 const char *con_id, 132 enum gpiod_flags flags) 133 134Device-managed variants of these functions are also defined:: 135 136 struct gpio_desc *devm_gpiod_get(struct device *dev, const char *con_id, 137 enum gpiod_flags flags) 138 139 struct gpio_desc *devm_gpiod_get_index(struct device *dev, 140 const char *con_id, 141 unsigned int idx, 142 enum gpiod_flags flags) 143 144 struct gpio_desc *devm_gpiod_get_optional(struct device *dev, 145 const char *con_id, 146 enum gpiod_flags flags) 147 148 struct gpio_desc *devm_gpiod_get_index_optional(struct device *dev, 149 const char *con_id, 150 unsigned int index, 151 enum gpiod_flags flags) 152 153 struct gpio_descs *devm_gpiod_get_array(struct device *dev, 154 const char *con_id, 155 enum gpiod_flags flags) 156 157 struct gpio_descs *devm_gpiod_get_array_optional(struct device *dev, 158 const char *con_id, 159 enum gpiod_flags flags) 160 161A GPIO descriptor can be disposed of using the gpiod_put() function:: 162 163 void gpiod_put(struct gpio_desc *desc) 164 165For an array of GPIOs this function can be used:: 166 167 void gpiod_put_array(struct gpio_descs *descs) 168 169It is strictly forbidden to use a descriptor after calling these functions. 170It is also not allowed to individually release descriptors (using gpiod_put()) 171from an array acquired with gpiod_get_array(). 172 173The device-managed variants are, unsurprisingly:: 174 175 void devm_gpiod_put(struct device *dev, struct gpio_desc *desc) 176 177 void devm_gpiod_put_array(struct device *dev, struct gpio_descs *descs) 178 179 180Using GPIOs 181=========== 182 183Setting Direction 184----------------- 185The first thing a driver must do with a GPIO is setting its direction. If no 186direction-setting flags have been given to gpiod_get*(), this is done by 187invoking one of the gpiod_direction_*() functions:: 188 189 int gpiod_direction_input(struct gpio_desc *desc) 190 int gpiod_direction_output(struct gpio_desc *desc, int value) 191 192The return value is zero for success, else a negative errno. It should be 193checked, since the get/set calls don't return errors and since misconfiguration 194is possible. You should normally issue these calls from a task context. However, 195for spinlock-safe GPIOs it is OK to use them before tasking is enabled, as part 196of early board setup. 197 198For output GPIOs, the value provided becomes the initial output value. This 199helps avoid signal glitching during system startup. 200 201A driver can also query the current direction of a GPIO:: 202 203 int gpiod_get_direction(const struct gpio_desc *desc) 204 205This function returns 0 for output, 1 for input, or an error code in case of error. 206 207Be aware that there is no default direction for GPIOs. Therefore, **using a GPIO 208without setting its direction first is illegal and will result in undefined 209behavior!** 210 211 212Spinlock-Safe GPIO Access 213------------------------- 214Most GPIO controllers can be accessed with memory read/write instructions. Those 215don't need to sleep, and can safely be done from inside hard (non-threaded) IRQ 216handlers and similar contexts. 217 218Use the following calls to access GPIOs from an atomic context:: 219 220 int gpiod_get_value(const struct gpio_desc *desc); 221 void gpiod_set_value(struct gpio_desc *desc, int value); 222 223The values are boolean, zero for inactive, nonzero for active. When reading the 224value of an output pin, the value returned should be what's seen on the pin. 225That won't always match the specified output value, because of issues including 226open-drain signaling and output latencies. 227 228The get/set calls do not return errors because "invalid GPIO" should have been 229reported earlier from gpiod_direction_*(). However, note that not all platforms 230can read the value of output pins; those that can't should always return zero. 231Also, using these calls for GPIOs that can't safely be accessed without sleeping 232(see below) is an error. 233 234 235GPIO Access That May Sleep 236-------------------------- 237Some GPIO controllers must be accessed using message based buses like I2C or 238SPI. Commands to read or write those GPIO values require waiting to get to the 239head of a queue to transmit a command and get its response. This requires 240sleeping, which can't be done from inside IRQ handlers. 241 242Platforms that support this type of GPIO distinguish them from other GPIOs by 243returning nonzero from this call:: 244 245 int gpiod_cansleep(const struct gpio_desc *desc) 246 247To access such GPIOs, a different set of accessors is defined:: 248 249 int gpiod_get_value_cansleep(const struct gpio_desc *desc) 250 void gpiod_set_value_cansleep(struct gpio_desc *desc, int value) 251 252Accessing such GPIOs requires a context which may sleep, for example a threaded 253IRQ handler, and those accessors must be used instead of spinlock-safe 254accessors without the cansleep() name suffix. 255 256Other than the fact that these accessors might sleep, and will work on GPIOs 257that can't be accessed from hardIRQ handlers, these calls act the same as the 258spinlock-safe calls. 259 260 261.. _active_low_semantics: 262 263The active low and open drain semantics 264--------------------------------------- 265As a consumer should not have to care about the physical line level, all of the 266gpiod_set_value_xxx() or gpiod_set_array_value_xxx() functions operate with 267the *logical* value. With this they take the active low property into account. 268This means that they check whether the GPIO is configured to be active low, 269and if so, they manipulate the passed value before the physical line level is 270driven. 271 272The same is applicable for open drain or open source output lines: those do not 273actively drive their output high (open drain) or low (open source), they just 274switch their output to a high impedance value. The consumer should not need to 275care. (For details read about open drain in driver.rst.) 276 277With this, all the gpiod_set_(array)_value_xxx() functions interpret the 278parameter "value" as "active" ("1") or "inactive" ("0"). The physical line 279level will be driven accordingly. 280 281As an example, if the active low property for a dedicated GPIO is set, and the 282gpiod_set_(array)_value_xxx() passes "active" ("1"), the physical line level 283will be driven low. 284 285To summarize:: 286 287 Function (example) line property physical line 288 gpiod_set_raw_value(desc, 0); don't care low 289 gpiod_set_raw_value(desc, 1); don't care high 290 gpiod_set_value(desc, 0); default (active high) low 291 gpiod_set_value(desc, 1); default (active high) high 292 gpiod_set_value(desc, 0); active low high 293 gpiod_set_value(desc, 1); active low low 294 gpiod_set_value(desc, 0); open drain low 295 gpiod_set_value(desc, 1); open drain high impedance 296 gpiod_set_value(desc, 0); open source high impedance 297 gpiod_set_value(desc, 1); open source high 298 299It is possible to override these semantics using the set_raw/get_raw functions 300but it should be avoided as much as possible, especially by system-agnostic drivers 301which should not need to care about the actual physical line level and worry about 302the logical value instead. 303 304 305Accessing raw GPIO values 306------------------------- 307Consumers exist that need to manage the logical state of a GPIO line, i.e. the value 308their device will actually receive, no matter what lies between it and the GPIO 309line. 310 311The following set of calls ignore the active-low or open drain property of a GPIO and 312work on the raw line value:: 313 314 int gpiod_get_raw_value(const struct gpio_desc *desc) 315 void gpiod_set_raw_value(struct gpio_desc *desc, int value) 316 int gpiod_get_raw_value_cansleep(const struct gpio_desc *desc) 317 void gpiod_set_raw_value_cansleep(struct gpio_desc *desc, int value) 318 int gpiod_direction_output_raw(struct gpio_desc *desc, int value) 319 320The active low state of a GPIO can also be queried and toggled using the 321following calls:: 322 323 int gpiod_is_active_low(const struct gpio_desc *desc) 324 void gpiod_toggle_active_low(struct gpio_desc *desc) 325 326Note that these functions should only be used with great moderation; a driver 327should not have to care about the physical line level or open drain semantics. 328 329 330Access multiple GPIOs with a single function call 331------------------------------------------------- 332The following functions get or set the values of an array of GPIOs:: 333 334 int gpiod_get_array_value(unsigned int array_size, 335 struct gpio_desc **desc_array, 336 struct gpio_array *array_info, 337 unsigned long *value_bitmap); 338 int gpiod_get_raw_array_value(unsigned int array_size, 339 struct gpio_desc **desc_array, 340 struct gpio_array *array_info, 341 unsigned long *value_bitmap); 342 int gpiod_get_array_value_cansleep(unsigned int array_size, 343 struct gpio_desc **desc_array, 344 struct gpio_array *array_info, 345 unsigned long *value_bitmap); 346 int gpiod_get_raw_array_value_cansleep(unsigned int array_size, 347 struct gpio_desc **desc_array, 348 struct gpio_array *array_info, 349 unsigned long *value_bitmap); 350 351 int gpiod_set_array_value(unsigned int array_size, 352 struct gpio_desc **desc_array, 353 struct gpio_array *array_info, 354 unsigned long *value_bitmap) 355 int gpiod_set_raw_array_value(unsigned int array_size, 356 struct gpio_desc **desc_array, 357 struct gpio_array *array_info, 358 unsigned long *value_bitmap) 359 int gpiod_set_array_value_cansleep(unsigned int array_size, 360 struct gpio_desc **desc_array, 361 struct gpio_array *array_info, 362 unsigned long *value_bitmap) 363 int gpiod_set_raw_array_value_cansleep(unsigned int array_size, 364 struct gpio_desc **desc_array, 365 struct gpio_array *array_info, 366 unsigned long *value_bitmap) 367 368The array can be an arbitrary set of GPIOs. The functions will try to access 369GPIOs belonging to the same bank or chip simultaneously if supported by the 370corresponding chip driver. In that case a significantly improved performance 371can be expected. If simultaneous access is not possible the GPIOs will be 372accessed sequentially. 373 374The functions take four arguments: 375 376 * array_size - the number of array elements 377 * desc_array - an array of GPIO descriptors 378 * array_info - optional information obtained from gpiod_get_array() 379 * value_bitmap - a bitmap to store the GPIOs' values (get) or 380 a bitmap of values to assign to the GPIOs (set) 381 382The descriptor array can be obtained using the gpiod_get_array() function 383or one of its variants. If the group of descriptors returned by that function 384matches the desired group of GPIOs, those GPIOs can be accessed by simply using 385the struct gpio_descs returned by gpiod_get_array():: 386 387 struct gpio_descs *my_gpio_descs = gpiod_get_array(...); 388 gpiod_set_array_value(my_gpio_descs->ndescs, my_gpio_descs->desc, 389 my_gpio_descs->info, my_gpio_value_bitmap); 390 391It is also possible to access a completely arbitrary array of descriptors. The 392descriptors may be obtained using any combination of gpiod_get() and 393gpiod_get_array(). Afterwards the array of descriptors has to be setup 394manually before it can be passed to one of the above functions. In that case, 395array_info should be set to NULL. 396 397Note that for optimal performance GPIOs belonging to the same chip should be 398contiguous within the array of descriptors. 399 400Still better performance may be achieved if array indexes of the descriptors 401match hardware pin numbers of a single chip. If an array passed to a get/set 402array function matches the one obtained from gpiod_get_array() and array_info 403associated with the array is also passed, the function may take a fast bitmap 404processing path, passing the value_bitmap argument directly to the respective 405.get/set_multiple() callback of the chip. That allows for utilization of GPIO 406banks as data I/O ports without much loss of performance. 407 408The return value of gpiod_get_array_value() and its variants is 0 on success 409or negative on error. Note the difference to gpiod_get_value(), which returns 4100 or 1 on success to convey the GPIO value. With the array functions, the GPIO 411values are stored in value_array rather than passed back as return value. 412 413 414GPIOs mapped to IRQs 415-------------------- 416GPIO lines can quite often be used as IRQs. You can get the IRQ number 417corresponding to a given GPIO using the following call:: 418 419 int gpiod_to_irq(const struct gpio_desc *desc) 420 421It will return an IRQ number, or a negative errno code if the mapping can't be 422done (most likely because that particular GPIO cannot be used as IRQ). It is an 423unchecked error to use a GPIO that wasn't set up as an input using 424gpiod_direction_input(), or to use an IRQ number that didn't originally come 425from gpiod_to_irq(). gpiod_to_irq() is not allowed to sleep. 426 427Non-error values returned from gpiod_to_irq() can be passed to request_irq() or 428free_irq(). They will often be stored into IRQ resources for platform devices, 429by the board-specific initialization code. Note that IRQ trigger options are 430part of the IRQ interface, e.g. IRQF_TRIGGER_FALLING, as are system wakeup 431capabilities. 432 433 434GPIOs and ACPI 435============== 436 437On ACPI systems, GPIOs are described by GpioIo()/GpioInt() resources listed by 438the _CRS configuration objects of devices. Those resources do not provide 439connection IDs (names) for GPIOs, so it is necessary to use an additional 440mechanism for this purpose. 441 442Systems compliant with ACPI 5.1 or newer may provide a _DSD configuration object 443which, among other things, may be used to provide connection IDs for specific 444GPIOs described by the GpioIo()/GpioInt() resources in _CRS. If that is the 445case, it will be handled by the GPIO subsystem automatically. However, if the 446_DSD is not present, the mappings between GpioIo()/GpioInt() resources and GPIO 447connection IDs need to be provided by device drivers. 448 449For details refer to Documentation/firmware-guide/acpi/gpio-properties.rst 450 451 452Interacting With the Legacy GPIO Subsystem 453========================================== 454Many kernel subsystems and drivers still handle GPIOs using the legacy 455integer-based interface. It is strongly recommended to update these to the new 456gpiod interface. For cases where both interfaces need to be used, the following 457two functions allow to convert a GPIO descriptor into the GPIO integer namespace 458and vice-versa:: 459 460 int desc_to_gpio(const struct gpio_desc *desc) 461 struct gpio_desc *gpio_to_desc(unsigned gpio) 462 463The GPIO number returned by desc_to_gpio() can safely be used as a parameter of 464the gpio\_*() functions for as long as the GPIO descriptor `desc` is not freed. 465All the same, a GPIO number passed to gpio_to_desc() must first be properly 466acquired using e.g. gpio_request_one(), and the returned GPIO descriptor is only 467considered valid until that GPIO number is released using gpio_free(). 468 469Freeing a GPIO obtained by one API with the other API is forbidden and an 470unchecked error. 471