summaryrefslogtreecommitdiffstats
path: root/Documentation/admin-guide/gpio/gpio-sim.rst
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /Documentation/admin-guide/gpio/gpio-sim.rst
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/admin-guide/gpio/gpio-sim.rst')
-rw-r--r--Documentation/admin-guide/gpio/gpio-sim.rst134
1 files changed, 134 insertions, 0 deletions
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