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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>
51 lines
1.9 KiB
ReStructuredText
51 lines
1.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0-only
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GPIO Testing Driver
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===================
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The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
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chips for testing purposes. The lines exposed by these chips can be accessed
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using the standard GPIO character device interface as well as manipulated
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using the dedicated debugfs directory structure.
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Creating simulated chips using module params
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--------------------------------------------
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When loading the gpio-mockup driver a number of parameters can be passed to the
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module.
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gpio_mockup_ranges
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This parameter takes an argument in the form of an array of integer
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pairs. Each pair defines the base GPIO number (if any) and the number
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of lines exposed by the chip. If the base GPIO is -1, the gpiolib
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will assign it automatically.
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Example: gpio_mockup_ranges=-1,8,-1,16,405,4
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The line above creates three chips. The first one will expose 8 lines,
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the second 16 and the third 4. The base GPIO for the third chip is set
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to 405 while for two first chips it will be assigned automatically.
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gpio_named_lines
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This parameter doesn't take any arguments. It lets the driver know that
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GPIO lines exposed by it should be named.
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The name format is: gpio-mockup-X-Y where X is mockup chip's ID
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and Y is the line offset.
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Manipulating simulated lines
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----------------------------
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Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
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The directory is named after the chip's label. A symlink is also created, named
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after the chip's name, which points to the label directory.
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Inside each subdirectory, there's a separate attribute for each GPIO line. The
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name of the attribute represents the line's offset in the chip.
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Reading from a line attribute returns the current value. Writing to it (0 or 1)
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changes the configuration of the simulated pull-up/pull-down resistor
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(1 - pull-up, 0 - pull-down).
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