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