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Diffstat (limited to 'Documentation/admin-guide/gpio/gpio-sim.rst')
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diff --git a/Documentation/admin-guide/gpio/gpio-sim.rst b/Documentation/admin-guide/gpio/gpio-sim.rst new file mode 100644 index 000000000..d8a90c81b --- /dev/null +++ b/Documentation/admin-guide/gpio/gpio-sim.rst @@ -0,0 +1,134 @@ +.. SPDX-License-Identifier: GPL-2.0-or-later + +Configfs GPIO Simulator +======================= + +The configfs GPIO Simulator (gpio-sim) provides a way to create simulated GPIO +chips for testing purposes. The lines exposed by these chips can be accessed +using the standard GPIO character device interface as well as manipulated +using sysfs attributes. + +Creating simulated chips +------------------------ + +The gpio-sim module registers a configfs subsystem called ``'gpio-sim'``. For +details of the configfs filesystem, please refer to the configfs documentation. + +The user can create a hierarchy of configfs groups and items as well as modify +values of exposed attributes. Once the chip is instantiated, this hierarchy +will be translated to appropriate device properties. The general structure is: + +**Group:** ``/config/gpio-sim`` + +This is the top directory of the gpio-sim configfs tree. + +**Group:** ``/config/gpio-sim/gpio-device`` + +**Attribute:** ``/config/gpio-sim/gpio-device/dev_name`` + +**Attribute:** ``/config/gpio-sim/gpio-device/live`` + +This is a directory representing a GPIO platform device. The ``'dev_name'`` +attribute is read-only and allows the user-space to read the platform device +name (e.g. ``'gpio-sim.0'``). The ``'live'`` attribute allows to trigger the +actual creation of the device once it's fully configured. The accepted values +are: ``'1'`` to enable the simulated device and ``'0'`` to disable and tear +it down. + +**Group:** ``/config/gpio-sim/gpio-device/gpio-bankX`` + +**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/chip_name`` + +**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/num_lines`` + +This group represents a bank of GPIOs under the top platform device. The +``'chip_name'`` attribute is read-only and allows the user-space to read the +device name of the bank device. The ``'num_lines'`` attribute allows to specify +the number of lines exposed by this bank. + +**Group:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY`` + +**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/name`` + +This group represents a single line at the offset Y. The 'name' attribute +allows to set the line name as represented by the 'gpio-line-names' property. + +**Item:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog`` + +**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog/name`` + +**Attribute:** ``/config/gpio-sim/gpio-device/gpio-bankX/lineY/hog/direction`` + +This item makes the gpio-sim module hog the associated line. The ``'name'`` +attribute specifies the in-kernel consumer name to use. The ``'direction'`` +attribute specifies the hog direction and must be one of: ``'input'``, +``'output-high'`` and ``'output-low'``. + +Inside each bank directory, there's a set of attributes that can be used to +configure the new chip. Additionally the user can ``mkdir()`` subdirectories +inside the chip's directory that allow to pass additional configuration for +specific lines. The name of those subdirectories must take the form of: +``'line<offset>'`` (e.g. ``'line0'``, ``'line20'``, etc.) as the name will be +used by the module to assign the config to the specific line at given offset. + +Once the confiuration is complete, the ``'live'`` attribute must be set to 1 in +order to instantiate the chip. It can be set back to 0 to destroy the simulated +chip. The module will synchronously wait for the new simulated device to be +successfully probed and if this doesn't happen, writing to ``'live'`` will +result in an error. + +Simulated GPIO chips can also be defined in device-tree. The compatible string +must be: ``"gpio-simulator"``. Supported properties are: + + ``"gpio-sim,label"`` - chip label + +Other standard GPIO properties (like ``"gpio-line-names"``, ``"ngpios"`` or +``"gpio-hog"``) are also supported. Please refer to the GPIO documentation for +details. + +An example device-tree code defining a GPIO simulator: + +.. code-block :: none + + gpio-sim { + compatible = "gpio-simulator"; + + bank0 { + gpio-controller; + #gpio-cells = <2>; + ngpios = <16>; + gpio-sim,label = "dt-bank0"; + gpio-line-names = "", "sim-foo", "", "sim-bar"; + }; + + bank1 { + gpio-controller; + #gpio-cells = <2>; + ngpios = <8>; + gpio-sim,label = "dt-bank1"; + + line3 { + gpio-hog; + gpios = <3 0>; + output-high; + line-name = "sim-hog-from-dt"; + }; + }; + }; + +Manipulating simulated lines +---------------------------- + +Each simulated GPIO chip creates a separate sysfs group under its device +directory for each exposed line +(e.g. ``/sys/devices/platform/gpio-sim.X/gpiochipY/``). The name of each group +is of the form: ``'sim_gpioX'`` where X is the offset of the line. Inside each +group there are two attibutes: + + ``pull`` - allows to read and set the current simulated pull setting for + every line, when writing the value must be one of: ``'pull-up'``, + ``'pull-down'`` + + ``value`` - allows to read the current value of the line which may be + different from the pull if the line is being driven from + user-space |