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