From: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx> There's some documentation for gpio-mockup's debugfs interface in the driver's source but it's not much. Add proper documentation for this testing module. Signed-off-by: Bartosz Golaszewski <bgolaszewski@xxxxxxxxxxxx> --- .../admin-guide/gpio/gpio-mockup.rst | 50 +++++++++++++++++++ 1 file changed, 50 insertions(+) create mode 100644 Documentation/admin-guide/gpio/gpio-mockup.rst diff --git a/Documentation/admin-guide/gpio/gpio-mockup.rst b/Documentation/admin-guide/gpio/gpio-mockup.rst new file mode 100644 index 000000000000..9fa1618b3adc --- /dev/null +++ b/Documentation/admin-guide/gpio/gpio-mockup.rst @@ -0,0 +1,50 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +GPIO Testing Driver +=================== + +The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO +chips for testing purposes. The lines exposed by these chips can be accessed +using the standard GPIO character device interface as well as manipulated +using the dedicated debugfs directory structure. + +Creating simulated chips using module params +-------------------------------------------- + +When loading the gpio-mockup driver a number of parameters can be passed to the +module. + + gpio_mockup_ranges + + This parameter takes an argument in the form of an array of integer + pairs. Each pair defines the base GPIO number (if any) and the number + of lines exposed by the chip. If the base GPIO is -1, the gpiolib + will assign it automatically. + + Example: gpio_mockup_ranges=-1,8,-1,16,405,4 + + The line above creates three chips. The first one will expose 8 lines, + the second 16 and the third 4. The base GPIO for the third chip is set + to 405 while for two first chips it will be assigned automatically. + + gpio_named_lines + + This parameter doesn't take any arguments. It lets the driver know that + GPIO lines exposed by it should be named. + + The name format is: gpio-mockup-X-Y where X is mockup chip's ID + and Y is the line offset. + +Manipulating simulated lines +---------------------------- + +Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/. +The directory is named after the chip's label. A symlink is also created, named +after the chip's name, which points to the label directory. + +Inside each subdirectory, there's a separate attribute for each GPIO line. The +name of the attribute represents the line's offset in the chip. + +Reading from a line attribute returns the current value. Writing to it (0 or 1) +changes the configuration of the simulated pull-up/pull-down resistor +(1 - pull-up, 0 - pull-down). -- 2.26.1
