0001 .. SPDX-License-Identifier: GPL-2.0-only
0002
0003 GPIO Testing Driver
0004 ===================
0005
0006 The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO
0007 chips for testing purposes. The lines exposed by these chips can be accessed
0008 using the standard GPIO character device interface as well as manipulated
0009 using the dedicated debugfs directory structure.
0010
0011 Creating simulated chips using module params
0012 --------------------------------------------
0013
0014 When loading the gpio-mockup driver a number of parameters can be passed to the
0015 module.
0016
0017 gpio_mockup_ranges
0018
0019 This parameter takes an argument in the form of an array of integer
0020 pairs. Each pair defines the base GPIO number (non-negative integer)
0021 and the first number after the last of this chip. If the base GPIO
0022 is -1, the gpiolib will assign it automatically. while the following
0023 parameter is the number of lines exposed by the chip.
0024
0025 Example: gpio_mockup_ranges=-1,8,-1,16,405,409
0026
0027 The line above creates three chips. The first one will expose 8 lines,
0028 the second 16 and the third 4. The base GPIO for the third chip is set
0029 to 405 while for two first chips it will be assigned automatically.
0030
0031 gpio_mockup_named_lines
0032
0033 This parameter doesn't take any arguments. It lets the driver know that
0034 GPIO lines exposed by it should be named.
0035
0036 The name format is: gpio-mockup-X-Y where X is mockup chip's ID
0037 and Y is the line offset.
0038
0039 Manipulating simulated lines
0040 ----------------------------
0041
0042 Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/.
0043 The directory is named after the chip's label. A symlink is also created, named
0044 after the chip's name, which points to the label directory.
0045
0046 Inside each subdirectory, there's a separate attribute for each GPIO line. The
0047 name of the attribute represents the line's offset in the chip.
0048
0049 Reading from a line attribute returns the current value. Writing to it (0 or 1)
0050 changes the configuration of the simulated pull-up/pull-down resistor
0051 (1 - pull-up, 0 - pull-down).
