1.. SPDX-License-Identifier: GPL-2.0-only 2 3GPIO Testing Driver 4=================== 5 6The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO 7chips for testing purposes. The lines exposed by these chips can be accessed 8using the standard GPIO character device interface as well as manipulated 9using the dedicated debugfs directory structure. 10 11Creating simulated chips using module params 12-------------------------------------------- 13 14When loading the gpio-mockup driver a number of parameters can be passed to the 15module. 16 17 gpio_mockup_ranges 18 19 This parameter takes an argument in the form of an array of integer 20 pairs. Each pair defines the base GPIO number (non-negative integer) 21 and the first number after the last of this chip. If the base GPIO 22 is -1, the gpiolib will assign it automatically. while the following 23 parameter is the number of lines exposed by the chip. 24 25 Example: gpio_mockup_ranges=-1,8,-1,16,405,409 26 27 The line above creates three chips. The first one will expose 8 lines, 28 the second 16 and the third 4. The base GPIO for the third chip is set 29 to 405 while for two first chips it will be assigned automatically. 30 31 gpio_mockup_named_lines 32 33 This parameter doesn't take any arguments. It lets the driver know that 34 GPIO lines exposed by it should be named. 35 36 The name format is: gpio-mockup-X-Y where X is mockup chip's ID 37 and Y is the line offset. 38 39Manipulating simulated lines 40---------------------------- 41 42Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/. 43The directory is named after the chip's label. A symlink is also created, named 44after the chip's name, which points to the label directory. 45 46Inside each subdirectory, there's a separate attribute for each GPIO line. The 47name of the attribute represents the line's offset in the chip. 48 49Reading from a line attribute returns the current value. Writing to it (0 or 1) 50changes the configuration of the simulated pull-up/pull-down resistor 51(1 - pull-up, 0 - pull-down). 52