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Documentation / gpio / drivers-on-gpio.txt


Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.

1	Subsystem drivers using GPIO
2	============================
3	
4	Note that standard kernel drivers exist for common GPIO tasks and will provide
5	the right in-kernel and userspace APIs/ABIs for the job, and that these
6	drivers can quite easily interconnect with other kernel subsystems using
7	hardware descriptions such as device tree or ACPI:
8	
9	- leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to  GPIO
10	  lines, giving you the LED sysfs interface
11	
12	- ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger,
13	  i.e. a LED will turn on/off in response to a GPIO line going high or low
14	  (and that LED may in turn use the leds-gpio as per above).
15	
16	- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
17	  can generate interrupts in response to a key press. Also supports debounce.
18	
19	- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
20	  GPIO line cannot generate interrupts, so it needs to be periodically polled
21	  by a timer.
22	
23	- gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with
24	  up to three buttons by simply using GPIOs and no mouse port. You can cut the
25	  mouse cable and connect the wires to GPIO lines or solder a mouse connector
26	  to the lines for a more permanent solution of this type.
27	
28	- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
29	  an external speaker connected to a GPIO line.
30	
31	- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
32	  external connector status, such as a headset line for an audio driver or an
33	  HDMI connector. It will provide a better userspace sysfs interface than GPIO.
34	
35	- restart-gpio: drivers/power/reset/gpio-restart.c is used to restart/reboot
36	  the system by pulling a GPIO line and will register a restart handler so
37	  userspace can issue the right system call to restart the system.
38	
39	- poweroff-gpio: drivers/power/reset/gpio-poweroff.c is used to power the
40	  system down by pulling a GPIO line and will register a pm_power_off()
41	  callback so that userspace can issue the right system call to power down the
42	  system.
43	
44	- gpio-gate-clock: drivers/clk/clk-gpio.c is used to control a gated clock
45	  (off/on) that uses a GPIO, and integrated with the clock subsystem.
46	
47	- i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus
48	  (two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will
49	  appear as any other I2C bus to the system and makes it possible to connect
50	  drivers for the I2C devices on the bus like any other I2C bus driver.
51	
52	- spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number
53	  of wires, at least SCK and optionally MISO, MOSI and chip select lines) using
54	  GPIO hammering (bitbang). It will appear as any other SPI bus on the system
55	  and makes it possible to connect drivers for SPI devices on the bus like
56	  any other SPI bus driver. For example any MMC/SD card can then be connected
57	  to this SPI by using the mmc_spi host from the MMC/SD card subsystem.
58	
59	- w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using
60	  a GPIO line, integrating with the W1 subsystem and handling devices on
61	  the bus like any other W1 device.
62	
63	- gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the
64	  system, connected to a GPIO line (and optionally a GPIO alarm line),
65	  presenting all the right in-kernel and sysfs interfaces to make your system
66	  not overheat.
67	
68	- gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a
69	  regulator providing a certain voltage by pulling a GPIO line, integrating
70	  with the regulator subsystem and giving you all the right interfaces.
71	
72	- gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer
73	  that will periodically "ping" a hardware connected to a GPIO line by toggling
74	  it from 1-to-0-to-1. If that hardware does not receive its "ping"
75	  periodically, it will reset the system.
76	
77	- gpio-nand: drivers/mtd/nand/gpio.c is used to connect a NAND flash chip to
78	  a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the
79	  NAND flash MTD subsystem and provides chip access and partition parsing like
80	  any other NAND driving hardware.
81	
82	- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
83	  bus, data and clock line, by bit banging two GPIO lines. It will appear as
84	  any other serio bus to the system and makes it possible to connect drivers
85	  for e.g. keyboards and other PS/2 protocol based devices.
86	
87	Apart from this there are special GPIO drivers in subsystems like MMC/SD to
88	read card detect and write protect GPIO lines, and in the TTY serial subsystem
89	to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
90	MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is
91	usually connected directly to the flash.
92	
93	Use those instead of talking directly to the GPIOs using sysfs; they integrate
94	with kernel frameworks better than your userspace code could. Needless to say,
95	just using the appropriate kernel drivers will simplify and speed up your
96	embedded hacking in particular by providing ready-made components.
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