Hi, On 9/4/20 8:45 AM, Bartosz Golaszewski wrote: > 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 | 87 +++++++++++++++++++ > 1 file changed, 87 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..1d452ee55f8d > --- /dev/null > +++ b/Documentation/admin-guide/gpio/gpio-mockup.rst > @@ -0,0 +1,87 @@ > +.. 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. There are two ways of configuring the chips exposed > +by the module. The lines can be accessed using the standard GPIO character > +device interface as well as manipulated using the dedicated debugfs directory > +structure. Could configfs be used for this instead of debugfs? debugfs is ad hoc. > + > +Creating simulated chips using debugfs > +-------------------------------------- > + > +When the gpio-mockup module is loaded (or builtin) it creates its own directory > +in debugfs. Assuming debugfs is mounted at /sys/kernel/debug/, the directory > +will be located at /sys/kernel/debug/gpio-mockup/. Inside this directory there > +are two attributes: new_device and delete_device. > + > +New chips can be created by writing a single line containing a number of > +options to "new_device". For example: > + > +.. code-block:: sh > + > + $ echo "label=my-mockup num_lines=4 named_lines" > /sys/kernel/debug/gpio-mockup/new_device > + > +Supported options: > + > + num_lines=<num_lines> - number of GPIO lines to expose > + > + label=<label> - label of the dummy chip > + > + named_lines - defines whether dummy lines should be named, the names are > + of the form X-Y where X is the chip's label and Y is the > + line's offset > + > +Note: only num_lines is mandatory. > + > +Chips can be dynamically removed by writing the chip's label to > +"delete_device". For example: > + > +.. code-block:: sh > + > + echo "gpio-mockup.0" > /sys/kernel/debug/gpio-mockup/delete_device > + > +Creating simulated chips using module params > +-------------------------------------------- > + > +Note: this is an older, now deprecated method kept for backward compatibility > +for user-space tools. > + > +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 the letter associated > + with the mockup chip and Y is the line offset. Where does this 'X' letter associated with the mockup chip come from? > + > +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 its pull. What does "pull" mean here? thanks. -- ~Randy
