1.. SPDX-License-Identifier: GPL-2.0-only 2 3GPIO Testing Driver 4=================== 5 6.. note:: 7 8 This module has been obsoleted by the more flexible gpio-sim.rst. 9 New developments should use that API and existing developments are 10 encouraged to migrate as soon as possible. 11 This module will continue to be maintained but no new features will be 12 added. 13 14The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO 15chips for testing purposes. The lines exposed by these chips can be accessed 16using the standard GPIO character device interface as well as manipulated 17using the dedicated debugfs directory structure. 18 19Creating simulated chips using module params 20-------------------------------------------- 21 22When loading the gpio-mockup driver a number of parameters can be passed to the 23module. 24 25 gpio_mockup_ranges 26 27 This parameter takes an argument in the form of an array of integer 28 pairs. Each pair defines the base GPIO number (non-negative integer) 29 and the first number after the last of this chip. If the base GPIO 30 is -1, the gpiolib will assign it automatically. while the following 31 parameter is the number of lines exposed by the chip. 32 33 Example: gpio_mockup_ranges=-1,8,-1,16,405,409 34 35 The line above creates three chips. The first one will expose 8 lines, 36 the second 16 and the third 4. The base GPIO for the third chip is set 37 to 405 while for two first chips it will be assigned automatically. 38 39 gpio_mockup_named_lines 40 41 This parameter doesn't take any arguments. It lets the driver know that 42 GPIO lines exposed by it should be named. 43 44 The name format is: gpio-mockup-X-Y where X is mockup chip's ID 45 and Y is the line offset. 46 47Manipulating simulated lines 48---------------------------- 49 50Each mockup chip creates its own subdirectory in /sys/kernel/debug/gpio-mockup/. 51The directory is named after the chip's label. A symlink is also created, named 52after the chip's name, which points to the label directory. 53 54Inside each subdirectory, there's a separate attribute for each GPIO line. The 55name of the attribute represents the line's offset in the chip. 56 57Reading from a line attribute returns the current value. Writing to it (0 or 1) 58changes the configuration of the simulated pull-up/pull-down resistor 59(1 - pull-up, 0 - pull-down). 60