1 ============================ 1 ============================
2 Subsystem drivers using GPIO 2 Subsystem drivers using GPIO
3 ============================ 3 ============================
4 4
5 Note that standard kernel drivers exist for co 5 Note that standard kernel drivers exist for common GPIO tasks and will provide
6 the right in-kernel and userspace APIs/ABIs fo 6 the right in-kernel and userspace APIs/ABIs for the job, and that these
7 drivers can quite easily interconnect with oth 7 drivers can quite easily interconnect with other kernel subsystems using
8 hardware descriptions such as device tree or A 8 hardware descriptions such as device tree or ACPI:
9 9
10 - leds-gpio: drivers/leds/leds-gpio.c will han 10 - leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to GPIO
11 lines, giving you the LED sysfs interface 11 lines, giving you the LED sysfs interface
12 12
13 - ledtrig-gpio: drivers/leds/trigger/ledtrig-g 13 - ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger,
14 i.e. a LED will turn on/off in response to a 14 i.e. a LED will turn on/off in response to a GPIO line going high or low
15 (and that LED may in turn use the leds-gpio 15 (and that LED may in turn use the leds-gpio as per above).
16 16
17 - gpio-keys: drivers/input/keyboard/gpio_keys. 17 - gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
18 can generate interrupts in response to a key 18 can generate interrupts in response to a key press. Also supports debounce.
19 19
20 - gpio-keys-polled: drivers/input/keyboard/gpi 20 - gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
21 GPIO line cannot generate interrupts, so it 21 GPIO line cannot generate interrupts, so it needs to be periodically polled
22 by a timer. 22 by a timer.
23 23
24 - gpio_mouse: drivers/input/mouse/gpio_mouse.c 24 - gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with
25 up to three buttons by simply using GPIOs an 25 up to three buttons by simply using GPIOs and no mouse port. You can cut the
26 mouse cable and connect the wires to GPIO li 26 mouse cable and connect the wires to GPIO lines or solder a mouse connector
27 to the lines for a more permanent solution o 27 to the lines for a more permanent solution of this type.
28 28
29 - gpio-beeper: drivers/input/misc/gpio-beeper. 29 - gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
30 an external speaker connected to a GPIO line 30 an external speaker connected to a GPIO line. (If the beep is controlled by
31 off/on, for an actual PWM waveform, see pwm- 31 off/on, for an actual PWM waveform, see pwm-gpio below.)
32 32
33 - pwm-gpio: drivers/pwm/pwm-gpio.c is used to 33 - pwm-gpio: drivers/pwm/pwm-gpio.c is used to toggle a GPIO with a high
34 resolution timer producing a PWM waveform on 34 resolution timer producing a PWM waveform on the GPIO line, as well as
35 Linux high resolution timers can do. 35 Linux high resolution timers can do.
36 36
37 - extcon-gpio: drivers/extcon/extcon-gpio.c is 37 - extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
38 external connector status, such as a headset 38 external connector status, such as a headset line for an audio driver or an
39 HDMI connector. It will provide a better use 39 HDMI connector. It will provide a better userspace sysfs interface than GPIO.
40 40
41 - restart-gpio: drivers/power/reset/gpio-resta 41 - restart-gpio: drivers/power/reset/gpio-restart.c is used to restart/reboot
42 the system by pulling a GPIO line and will r 42 the system by pulling a GPIO line and will register a restart handler so
43 userspace can issue the right system call to 43 userspace can issue the right system call to restart the system.
44 44
45 - poweroff-gpio: drivers/power/reset/gpio-powe 45 - poweroff-gpio: drivers/power/reset/gpio-poweroff.c is used to power the
46 system down by pulling a GPIO line and will 46 system down by pulling a GPIO line and will register a pm_power_off()
47 callback so that userspace can issue the rig 47 callback so that userspace can issue the right system call to power down the
48 system. 48 system.
49 49
50 - gpio-gate-clock: drivers/clk/clk-gpio.c is u 50 - gpio-gate-clock: drivers/clk/clk-gpio.c is used to control a gated clock
51 (off/on) that uses a GPIO, and integrated wi 51 (off/on) that uses a GPIO, and integrated with the clock subsystem.
52 52
53 - i2c-gpio: drivers/i2c/busses/i2c-gpio.c is u 53 - i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus
54 (two wires, SDA and SCL lines) by hammering 54 (two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will
55 appear as any other I2C bus to the system an 55 appear as any other I2C bus to the system and makes it possible to connect
56 drivers for the I2C devices on the bus like 56 drivers for the I2C devices on the bus like any other I2C bus driver.
57 57
58 - spi_gpio: drivers/spi/spi-gpio.c is used to 58 - spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number
59 of wires, at least SCK and optionally MISO, 59 of wires, at least SCK and optionally MISO, MOSI and chip select lines) using
60 GPIO hammering (bitbang). It will appear as 60 GPIO hammering (bitbang). It will appear as any other SPI bus on the system
61 and makes it possible to connect drivers for 61 and makes it possible to connect drivers for SPI devices on the bus like
62 any other SPI bus driver. For example any MM 62 any other SPI bus driver. For example any MMC/SD card can then be connected
63 to this SPI by using the mmc_spi host from t 63 to this SPI by using the mmc_spi host from the MMC/SD card subsystem.
64 64
65 - w1-gpio: drivers/w1/masters/w1-gpio.c is use 65 - w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using
66 a GPIO line, integrating with the W1 subsyst 66 a GPIO line, integrating with the W1 subsystem and handling devices on
67 the bus like any other W1 device. 67 the bus like any other W1 device.
68 68
69 - gpio-fan: drivers/hwmon/gpio-fan.c is used t 69 - gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the
70 system, connected to a GPIO line (and option 70 system, connected to a GPIO line (and optionally a GPIO alarm line),
71 presenting all the right in-kernel and sysfs 71 presenting all the right in-kernel and sysfs interfaces to make your system
72 not overheat. 72 not overheat.
73 73
74 - gpio-regulator: drivers/regulator/gpio-regul 74 - gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a
75 regulator providing a certain voltage by pul 75 regulator providing a certain voltage by pulling a GPIO line, integrating
76 with the regulator subsystem and giving you 76 with the regulator subsystem and giving you all the right interfaces.
77 77
78 - gpio-wdt: drivers/watchdog/gpio_wdt.c is use 78 - gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer
79 that will periodically "ping" a hardware con 79 that will periodically "ping" a hardware connected to a GPIO line by toggling
80 it from 1-to-0-to-1. If that hardware does n 80 it from 1-to-0-to-1. If that hardware does not receive its "ping"
81 periodically, it will reset the system. 81 periodically, it will reset the system.
82 82
83 - gpio-nand: drivers/mtd/nand/raw/gpio.c is us 83 - gpio-nand: drivers/mtd/nand/raw/gpio.c is used to connect a NAND flash chip
84 to a set of simple GPIO lines: RDY, NCE, ALE 84 to a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the
85 NAND flash MTD subsystem and provides chip a 85 NAND flash MTD subsystem and provides chip access and partition parsing like
86 any other NAND driving hardware. 86 any other NAND driving hardware.
87 87
88 - ps2-gpio: drivers/input/serio/ps2-gpio.c is 88 - ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
89 bus, data and clock line, by bit banging two 89 bus, data and clock line, by bit banging two GPIO lines. It will appear as
90 any other serio bus to the system and makes 90 any other serio bus to the system and makes it possible to connect drivers
91 for e.g. keyboards and other PS/2 protocol b 91 for e.g. keyboards and other PS/2 protocol based devices.
92 92
93 - cec-gpio: drivers/media/platform/cec-gpio/ i 93 - cec-gpio: drivers/media/platform/cec-gpio/ is used to interact with a CEC
94 Consumer Electronics Control bus using only 94 Consumer Electronics Control bus using only GPIO. It is used to communicate
95 with devices on the HDMI bus. 95 with devices on the HDMI bus.
96 96
97 - gpio-charger: drivers/power/supply/gpio-char 97 - gpio-charger: drivers/power/supply/gpio-charger.c is used if you need to do
98 battery charging and all you have to go by t 98 battery charging and all you have to go by to check the presence of the
99 AC charger or more complex tasks such as ind 99 AC charger or more complex tasks such as indicating charging status using
100 nothing but GPIO lines, this driver provides 100 nothing but GPIO lines, this driver provides that and also a clearly defined
101 way to pass the charging parameters from har 101 way to pass the charging parameters from hardware descriptions such as the
102 device tree. 102 device tree.
103 103
104 - gpio-mux: drivers/mux/gpio.c is used for con 104 - gpio-mux: drivers/mux/gpio.c is used for controlling a multiplexer using
105 n GPIO lines such that you can mux in 2^n di 105 n GPIO lines such that you can mux in 2^n different devices by activating
106 different GPIO lines. Often the GPIOs are on 106 different GPIO lines. Often the GPIOs are on a SoC and the devices are
107 some SoC-external entities, such as differen 107 some SoC-external entities, such as different components on a PCB that
108 can be selectively enabled. 108 can be selectively enabled.
109 109
110 Apart from this there are special GPIO drivers 110 Apart from this there are special GPIO drivers in subsystems like MMC/SD to
111 read card detect and write protect GPIO lines, 111 read card detect and write protect GPIO lines, and in the TTY serial subsystem
112 to emulate MCTRL (modem control) signals CTS/R 112 to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
113 MTD NOR flash has add-ons for extra GPIO lines 113 MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is
114 usually connected directly to the flash. 114 usually connected directly to the flash.
115 115
116 Use those instead of talking directly to the G 116 Use those instead of talking directly to the GPIOs from userspace; they
117 integrate with kernel frameworks better than y 117 integrate with kernel frameworks better than your userspace code could.
118 Needless to say, just using the appropriate ke 118 Needless to say, just using the appropriate kernel drivers will simplify and
119 speed up your embedded hacking in particular b 119 speed up your embedded hacking in particular by providing ready-made components.
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