Lines Matching +full:int +full:- +full:gpios
13 A "General Purpose Input/Output" (GPIO) is a flexible software-controlled
18 which GPIOs. Drivers can be written generically, so that board setup code
21 System-on-Chip (SOC) processors heavily rely on GPIOs. In some cases, every
22 non-dedicated pin can be configured as a GPIO; and most chips have at least
24 provide GPIOs; multifunction chips like power managers, and audio codecs
27 Most PC southbridges have a few dozen GPIO-capable pins (with only the BIOS
30 The exact capabilities of GPIOs vary between systems. Common options:
32 - Output values are writable (high=1, low=0). Some chips also have
34 value might be driven ... supporting "wire-OR" and similar schemes
37 - Input values are likewise readable (1, 0). Some chips support readback
38 of pins configured as "output", which is very useful in such "wire-OR"
40 input de-glitch/debounce logic, sometimes with software controls.
42 - Inputs can often be used as IRQ signals, often edge triggered but
46 - Usually a GPIO will be configurable as either input or output, as needed
49 - Most GPIOs can be accessed while holding spinlocks, but those accessed
62 is not the main issue; GPIOs are often used for the kind of board-specific
64 used on a board that's wired differently. Only least-common-denominator
65 functionality can be very portable. Other features are platform-specific,
80 GPIO calls are available, either as "real code" or as optimized-away stubs,
92 Identifying GPIOs
93 -----------------
94 GPIOs are identified by unsigned integers in the range 0..MAX_INT. That
100 for the GPIO lines so that board-specific setup code directly corresponds
103 board-specific pin configuration data (along with other board specific
106 So for example one platform uses numbers 32-159 for GPIOs; while another
107 uses numbers 0..63 with one set of GPIO controllers, 64-79 with another
108 type of GPIO controller, and on one particular board 80-95 with an FPGA.
110 use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders.
113 some negative number (perhaps "-EINVAL"); that will never be valid. To
117 int gpio_is_valid(int number);
120 or free GPIOs (see below). Other numbers may also be rejected; for
123 Whether a platform supports multiple GPIO controllers is a platform-specific
128 Using GPIOs
129 -----------
137 int gpio_direction_input(unsigned gpio);
138 int gpio_direction_output(unsigned gpio, int value);
143 a task context. However, for spinlock-safe GPIOs it's OK to use them
146 For output GPIOs, the value provided becomes the initial output value.
149 For compatibility with legacy interfaces to GPIOs, setting the direction
162 Spinlock-Safe GPIO access
163 -------------------------
168 Use the following calls to access such GPIOs,
172 int gpio_get_value(unsigned gpio);
175 void gpio_set_value(unsigned gpio, int value);
180 issues including open-drain signaling and output latencies.
185 return zero. Also, using these calls for GPIOs that can't safely be accessed
188 Platform-specific implementations are encouraged to optimize the two
198 --------------------------
204 Platforms that support this type of GPIO distinguish them from other GPIOs
208 int gpio_cansleep(unsigned gpio);
210 To access such GPIOs, a different set of accessors is defined::
213 int gpio_get_value_cansleep(unsigned gpio);
216 void gpio_set_value_cansleep(unsigned gpio, int value);
219 Accessing such GPIOs requires a context which may sleep, for example
221 spinlock-safe accessors without the cansleep() name suffix.
224 on GPIOs that can't be accessed from hardIRQ handlers, these calls act
225 the same as the spinlock-safe calls.
227 **IN ADDITION** calls to setup and configure such GPIOs must be made
245 Claiming and Releasing GPIOs
246 ----------------------------
250 * non-null labels may be useful for diagnostics.
252 int gpio_request(unsigned gpio, const char *label);
254 /* release previously-claimed GPIO */
258 GPIOs that have already been claimed with that call. The return value of
260 a task context. However, for spinlock-safe GPIOs it's OK to request GPIOs
264 are actually in use as GPIOs, for better diagnostics; systems may have
265 several hundred potential GPIOs, but often only a dozen are used on any
272 Some platforms may also use knowledge about what GPIOs are active for
276 For GPIOs that use pins known to the pinctrl subsystem, that subsystem should
286 setup of an output GPIO's value. This allows a glitch-free migration from a
288 to implement a workaround on signals typically driven by a non-GPIO HW block.
293 configured prior to gpio_request() being called for those GPIOs, e.g. using
300 Considering in most cases GPIOs are actually configured right after they
307 int gpio_request_one(unsigned gpio, unsigned long flags, const char *label);
309 /* request multiple GPIOs in a single call
311 int gpio_request_array(struct gpio *array, size_t num);
313 /* release multiple GPIOs in a single call
319 * GPIOF_DIR_IN - to configure direction as input
320 * GPIOF_DIR_OUT - to configure direction as output
322 * GPIOF_INIT_LOW - as output, set initial level to LOW
323 * GPIOF_INIT_HIGH - as output, set initial level to HIGH
324 * GPIOF_OPEN_DRAIN - gpio pin is open drain type.
325 * GPIOF_OPEN_SOURCE - gpio pin is open source type.
327 * GPIOF_EXPORT_DIR_FIXED - export gpio to sysfs, keep direction
328 * GPIOF_EXPORT_DIR_CHANGEABLE - also export, allow changing direction
333 * GPIOF_IN - configure as input
334 * GPIOF_OUT_INIT_LOW - configured as output, initial level LOW
335 * GPIOF_OUT_INIT_HIGH - configured as output, initial level HIGH
339 require to connect pull-up on such pins. By enabling this flag, gpio lib will
345 require to connect pull-down on such pin. By enabling this flag, gpio lib will
351 Further more, to ease the claim/release of multiple GPIOs, 'struct gpio' is
381 GPIOs mapped to IRQs
382 --------------------
388 int gpio_to_irq(unsigned gpio);
391 int irq_to_gpio(unsigned irq);
395 some GPIOs can't be used as IRQs.) It is an unchecked error to use a GPIO
402 Non-error values returned from gpio_to_irq() can be passed to request_irq()
404 devices, by the board-specific initialization code. Note that IRQ trigger
408 Non-error values returned from irq_to_gpio() would most commonly be used
410 when the IRQ is edge-triggered. Note that some platforms don't support
415 ----------------------------
419 level. This is sometimes called a "wire-AND"; or more practically, from the
420 negative logic (low=true) perspective this is a "wire-OR".
422 One common example of an open drain signal is a shared active-low IRQ line.
445 ------------------------------------------
458 But how does the pin control subsystem cross-correlate the GPIO
463 cross-reference tables. These are described in
464 Documentation/driver-api/pin-control.rst
480 For non-DT support, user can call gpiochip_add_pin_range() with appropriate
489 this is highly chip-specific and nonportable. One platform might not need
498 pullups (or pulldowns) so that the on-chip ones should not be used.
499 (When a circuit needs 5 kOhm, on-chip 100 kOhm resistors won't do.)
501 platform-specific issue, as are models like (not) having a one-to-one
502 correspondence between configurable pins and GPIOs.
504 There are other system-specific mechanisms that are not specified here,
505 like the aforementioned options for input de-glitching and wire-OR output.
506 Hardware may support reading or writing GPIOs in gangs, but that's usually
507 configuration dependent: for GPIOs sharing the same bank. (GPIOs are
509 banks.) Some systems can trigger IRQs from output GPIOs, or read values
510 from pins not managed as GPIOs. Code relying on such mechanisms will
513 Dynamic definition of GPIOs is not currently standard; for example, as
514 a side effect of configuring an add-on board with some GPIO expanders.
525 this framework, and the state of the GPIOs currently in use.
529 -----------------------------
533 - methods to establish GPIO direction
534 - methods used to access GPIO values
535 - flag saying whether calls to its methods may sleep
536 - optional debugfs dump method (showing extra state like pullup config)
537 - label for diagnostics
539 There is also per-instance data, which may come from device.platform_data:
540 the number of its first GPIO, and how many GPIOs it exposes.
547 Most often a gpio_chip is part of an instance-specific structure with state
549 and more. Chips such as codecs will have complex non-GPIO state.
552 requested as GPIOs. They can use gpiochip_is_requested(), which returns
557 ----------------
558 To force-enable this framework, a platform's Kconfig will "select" GPIOLIB,
562 reflects the number of GPIOs in actual use on that platform, without
563 wasting static table space. (It should count both built-in/SoC GPIOs and
567 GPIOs through GPIO-lib and the code cannot be enabled by the user.
577 logic optimizing access to specific SOC-based GPIOs. For example, if the
584 For SOCs, platform-specific code defines and registers gpio_chip instances
585 for each bank of on-chip GPIOs. Those GPIOs should be numbered/labeled to
587 may well start at zero and go up to a platform-specific limit. Such GPIOs
593 -------------
594 For external GPIO controllers -- such as I2C or SPI expanders, ASICs, multi
595 function devices, FPGAs or CPLDs -- most often board-specific code handles
598 platform-specific GPIOs.
601 of GPIOs that chip will expose, and passes them to each GPIO expander chip
606 an I2C-based GPIO, its probe() routine should only be called after that GPIO
618 configure a sysfs user interface to GPIOs. This is different from the
627 then changing its output state, then updating the code before re-enabling
637 GPIO tasks: "leds-gpio" and "gpio_keys", respectively. Use those
638 instead of talking directly to the GPIOs; they integrate with kernel
643 --------------
646 - Control interfaces used to get userspace control over GPIOs;
648 - GPIOs themselves; and
650 - GPIO controllers ("gpio_chip" instances).
654 The control interfaces are write-only:
689 If the pin can be configured as interrupt-generating interrupt
696 new value or close the file and re-open it to read the value.
713 controller implementing GPIOs starting at #42) and have the following
714 read-only attributes:
722 "ngpio" ... how many GPIOs this manges (N to N + ngpio - 1)
724 Board documentation should in most cases cover what GPIOs are used for
725 what purposes. However, those numbers are not always stable; GPIOs on
733 --------------------------
734 Kernel code can explicitly manage exports of GPIOs which have already been
738 int gpio_export(unsigned gpio, bool direction_may_change);
744 int gpio_export_link(struct device *dev, const char *name,
753 of experiments easier), or can provide an always-there interface that's
768 .. kernel-doc:: drivers/gpio/gpiolib-legacy.c