Lines Matching +full:platform +full:- +full:specific
13 A "General Purpose Input/Output" (GPIO) is a flexible software-controlled
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
27 Most PC southbridges have a few dozen GPIO-capable pins (with only the BIOS
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
52 On a given board each GPIO is used for one specific purpose like monitoring
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,
69 One platform might implement it as simple inline functions accessing chip
76 That said, if the convention is supported on their platform, drivers should
80 GPIO calls are available, either as "real code" or as optimized-away stubs,
93 -----------------
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
123 Whether a platform supports multiple GPIO controllers is a platform-specific
129 -----------
143 a task context. However, for spinlock-safe GPIOs it's OK to use them
162 Spinlock-Safe GPIO access
163 -------------------------
180 issues including open-drain signaling and output latencies.
188 Platform-specific implementations are encouraged to optimize the two
198 --------------------------
221 spinlock-safe accessors without the cansleep() name suffix.
225 the same as the spinlock-safe calls.
246 ----------------------------
250 * non-null labels may be useful for diagnostics.
254 /* release previously-claimed GPIO */
260 a task context. However, for spinlock-safe GPIOs it's OK to request GPIOs
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.
292 pullup/pulldown. Platform software should arrange that any such details are
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
382 --------------------
402 Non-error values returned from gpio_to_irq() can be passed to request_irq()
403 or free_irq(). They will often be stored into IRQ resources for platform
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/pinctl.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
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.
514 a side effect of configuring an add-on board with some GPIO expanders.
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:
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.
556 Platform Support
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
566 If neither of these options are selected, the platform does not support
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
588 are normally integrated into platform initialization to make them always be
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.
606 an I2C-based GPIO, its probe() routine should only be called after that GPIO
610 board specific code; those board specific callbacks would register devices
627 then changing its output state, then updating the code before re-enabling
637 GPIO tasks: "leds-gpio" and "gpio_keys", respectively. Use those
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.
714 read-only attributes:
722 "ngpio" ... how many GPIOs this manges (N to N + ngpio - 1)
733 --------------------------
753 of experiments easier), or can provide an always-there interface that's
768 .. kernel-doc:: drivers/gpio/gpiolib-legacy.c