102 lines
5.3 KiB
ReStructuredText
102 lines
5.3 KiB
ReStructuredText
============================
|
|
Subsystem drivers using GPIO
|
|
============================
|
|
|
|
Note that standard kernel drivers exist for common GPIO tasks and will provide
|
|
the right in-kernel and userspace APIs/ABIs for the job, and that these
|
|
drivers can quite easily interconnect with other kernel subsystems using
|
|
hardware descriptions such as device tree or ACPI:
|
|
|
|
- leds-gpio: drivers/leds/leds-gpio.c will handle LEDs connected to GPIO
|
|
lines, giving you the LED sysfs interface
|
|
|
|
- ledtrig-gpio: drivers/leds/trigger/ledtrig-gpio.c will provide a LED trigger,
|
|
i.e. a LED will turn on/off in response to a GPIO line going high or low
|
|
(and that LED may in turn use the leds-gpio as per above).
|
|
|
|
- gpio-keys: drivers/input/keyboard/gpio_keys.c is used when your GPIO line
|
|
can generate interrupts in response to a key press. Also supports debounce.
|
|
|
|
- gpio-keys-polled: drivers/input/keyboard/gpio_keys_polled.c is used when your
|
|
GPIO line cannot generate interrupts, so it needs to be periodically polled
|
|
by a timer.
|
|
|
|
- gpio_mouse: drivers/input/mouse/gpio_mouse.c is used to provide a mouse with
|
|
up to three buttons by simply using GPIOs and no mouse port. You can cut the
|
|
mouse cable and connect the wires to GPIO lines or solder a mouse connector
|
|
to the lines for a more permanent solution of this type.
|
|
|
|
- gpio-beeper: drivers/input/misc/gpio-beeper.c is used to provide a beep from
|
|
an external speaker connected to a GPIO line.
|
|
|
|
- extcon-gpio: drivers/extcon/extcon-gpio.c is used when you need to read an
|
|
external connector status, such as a headset line for an audio driver or an
|
|
HDMI connector. It will provide a better userspace sysfs interface than GPIO.
|
|
|
|
- restart-gpio: drivers/power/reset/gpio-restart.c is used to restart/reboot
|
|
the system by pulling a GPIO line and will register a restart handler so
|
|
userspace can issue the right system call to restart the system.
|
|
|
|
- poweroff-gpio: drivers/power/reset/gpio-poweroff.c is used to power the
|
|
system down by pulling a GPIO line and will register a pm_power_off()
|
|
callback so that userspace can issue the right system call to power down the
|
|
system.
|
|
|
|
- gpio-gate-clock: drivers/clk/clk-gpio.c is used to control a gated clock
|
|
(off/on) that uses a GPIO, and integrated with the clock subsystem.
|
|
|
|
- i2c-gpio: drivers/i2c/busses/i2c-gpio.c is used to drive an I2C bus
|
|
(two wires, SDA and SCL lines) by hammering (bitbang) two GPIO lines. It will
|
|
appear as any other I2C bus to the system and makes it possible to connect
|
|
drivers for the I2C devices on the bus like any other I2C bus driver.
|
|
|
|
- spi_gpio: drivers/spi/spi-gpio.c is used to drive an SPI bus (variable number
|
|
of wires, at least SCK and optionally MISO, MOSI and chip select lines) using
|
|
GPIO hammering (bitbang). It will appear as any other SPI bus on the system
|
|
and makes it possible to connect drivers for SPI devices on the bus like
|
|
any other SPI bus driver. For example any MMC/SD card can then be connected
|
|
to this SPI by using the mmc_spi host from the MMC/SD card subsystem.
|
|
|
|
- w1-gpio: drivers/w1/masters/w1-gpio.c is used to drive a one-wire bus using
|
|
a GPIO line, integrating with the W1 subsystem and handling devices on
|
|
the bus like any other W1 device.
|
|
|
|
- gpio-fan: drivers/hwmon/gpio-fan.c is used to control a fan for cooling the
|
|
system, connected to a GPIO line (and optionally a GPIO alarm line),
|
|
presenting all the right in-kernel and sysfs interfaces to make your system
|
|
not overheat.
|
|
|
|
- gpio-regulator: drivers/regulator/gpio-regulator.c is used to control a
|
|
regulator providing a certain voltage by pulling a GPIO line, integrating
|
|
with the regulator subsystem and giving you all the right interfaces.
|
|
|
|
- gpio-wdt: drivers/watchdog/gpio_wdt.c is used to provide a watchdog timer
|
|
that will periodically "ping" a hardware connected to a GPIO line by toggling
|
|
it from 1-to-0-to-1. If that hardware does not receive its "ping"
|
|
periodically, it will reset the system.
|
|
|
|
- gpio-nand: drivers/mtd/nand/raw/gpio.c is used to connect a NAND flash chip
|
|
to a set of simple GPIO lines: RDY, NCE, ALE, CLE, NWP. It interacts with the
|
|
NAND flash MTD subsystem and provides chip access and partition parsing like
|
|
any other NAND driving hardware.
|
|
|
|
- ps2-gpio: drivers/input/serio/ps2-gpio.c is used to drive a PS/2 (IBM) serio
|
|
bus, data and clock line, by bit banging two GPIO lines. It will appear as
|
|
any other serio bus to the system and makes it possible to connect drivers
|
|
for e.g. keyboards and other PS/2 protocol based devices.
|
|
|
|
- cec-gpio: drivers/media/platform/cec-gpio/ is used to interact with a CEC
|
|
Consumer Electronics Control bus using only GPIO. It is used to communicate
|
|
with devices on the HDMI bus.
|
|
|
|
Apart from this there are special GPIO drivers in subsystems like MMC/SD to
|
|
read card detect and write protect GPIO lines, and in the TTY serial subsystem
|
|
to emulate MCTRL (modem control) signals CTS/RTS by using two GPIO lines. The
|
|
MTD NOR flash has add-ons for extra GPIO lines too, though the address bus is
|
|
usually connected directly to the flash.
|
|
|
|
Use those instead of talking directly to the GPIOs from userspace; they
|
|
integrate with kernel frameworks better than your userspace code could.
|
|
Needless to say, just using the appropriate kernel drivers will simplify and
|
|
speed up your embedded hacking in particular by providing ready-made components.
|