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1.. SPDX-License-Identifier: GPL-2.0-only2 3GPIO Testing Driver4===================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 are10 encouraged to migrate as soon as possible.11 This module will continue to be maintained but no new features will be12 added.13 14The GPIO Testing Driver (gpio-mockup) provides a way to create simulated GPIO15chips for testing purposes. The lines exposed by these chips can be accessed16using the standard GPIO character device interface as well as manipulated17using the dedicated debugfs directory structure.18 19Creating simulated chips using module params20--------------------------------------------21 22When loading the gpio-mockup driver a number of parameters can be passed to the23module.24 25 gpio_mockup_ranges26 27 This parameter takes an argument in the form of an array of integer28 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 GPIO30 is -1, the gpiolib will assign it automatically. while the following31 parameter is the number of lines exposed by the chip.32 33 Example: gpio_mockup_ranges=-1,8,-1,16,405,40934 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 set37 to 405 while for two first chips it will be assigned automatically.38 39 gpio_mockup_named_lines40 41 This parameter doesn't take any arguments. It lets the driver know that42 GPIO lines exposed by it should be named.43 44 The name format is: gpio-mockup-X-Y where X is mockup chip's ID45 and Y is the line offset.46 47Manipulating simulated lines48----------------------------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, named52after the chip's name, which points to the label directory.53 54Inside each subdirectory, there's a separate attribute for each GPIO line. The55name 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 resistor59(1 - pull-up, 0 - pull-down).60