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[v3,02/10] Documentation: gpio: add documentation for gpio-mockup

Message ID 20200929101004.20288-3-brgl@bgdev.pl
State New
Headers show
Series gpio: mockup: refactoring + documentation | expand

Commit Message

Bartosz Golaszewski Sept. 29, 2020, 10:09 a.m. UTC
From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

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@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
 .../admin-guide/gpio/gpio-mockup.rst          | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 Documentation/admin-guide/gpio/gpio-mockup.rst
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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
+    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).