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Diffstat (limited to 'Documentation/admin-guide/gpio/gpio-virtuser.rst')
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diff --git a/Documentation/admin-guide/gpio/gpio-virtuser.rst b/Documentation/admin-guide/gpio/gpio-virtuser.rst new file mode 100644 index 000000000000..2aca70db9f3b --- /dev/null +++ b/Documentation/admin-guide/gpio/gpio-virtuser.rst @@ -0,0 +1,177 @@ +.. SPDX-License-Identifier: GPL-2.0-only + +Virtual GPIO Consumer +===================== + +The virtual GPIO Consumer module allows users to instantiate virtual devices +that request GPIOs and then control their behavior over debugfs. Virtual +consumer devices can be instantiated from device-tree or over configfs. + +A virtual consumer uses the driver-facing GPIO APIs and allows to cover it with +automated tests driven by user-space. The GPIOs are requested using +``gpiod_get_array()`` and so we support multiple GPIOs per connector ID. + +Creating GPIO consumers +----------------------- + +The gpio-consumer module registers a configfs subsystem called +``'gpio-virtuser'``. 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 consumer is instantiated, this hierarchy +will be translated to appropriate device properties. The general structure is: + +**Group:** ``/config/gpio-virtuser`` + +This is the top directory of the gpio-consumer configfs tree. + +**Group:** ``/config/gpio-consumer/example-name`` + +**Attribute:** ``/config/gpio-consumer/example-name/live`` + +**Attribute:** ``/config/gpio-consumer/example-name/dev_name`` + +This is a directory representing a GPIO consumer device. + +The read-only ``dev_name`` attribute exposes the name of the device as it will +appear in the system on the platform bus. This is useful for locating the +associated debugfs directory under +``/sys/kernel/debug/gpio-virtuser/$dev_name``. + +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 +virtual device and ``'0'`` to disable and tear it down. + +Creating GPIO lookup tables +--------------------------- + +Users can create a number of configfs groups under the device group: + +**Group:** ``/config/gpio-consumer/example-name/con_id`` + +The ``'con_id'`` directory represents a single GPIO lookup and its value maps +to the ``'con_id'`` argument of the ``gpiod_get()`` function. For example: +``con_id`` == ``'reset'`` maps to the ``reset-gpios`` device property. + +Users can assign a number of GPIOs to each lookup. Each GPIO is a sub-directory +with a user-defined name under the ``'con_id'`` group. + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/key`` + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/offset`` + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/drive`` + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/pull`` + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/active_low`` + +**Attribute:** ``/config/gpio-consumer/example-name/con_id/0/transitory`` + +This is a group describing a single GPIO in the ``con_id-gpios`` property. + +For virtual consumers created using configfs we use machine lookup tables so +this group can be considered as a mapping between the filesystem and the fields +of a single entry in ``'struct gpiod_lookup'``. + +The ``'key'`` attribute represents either the name of the chip this GPIO +belongs to or the GPIO line name. This depends on the value of the ``'offset'`` +attribute: if its value is >= 0, then ``'key'`` represents the label of the +chip to lookup while ``'offset'`` represents the offset of the line in that +chip. If ``'offset'`` is < 0, then ``'key'`` represents the name of the line. + +The remaining attributes map to the ``'flags'`` field of the GPIO lookup +struct. The first two take string values as arguments: + +**``'drive'``:** ``'push-pull'``, ``'open-drain'``, ``'open-source'`` +**``'pull'``:** ``'pull-up'``, ``'pull-down'``, ``'pull-disabled'``, ``'as-is'`` + +``'active_low'`` and ``'transitory'`` are boolean attributes. + +Activating GPIO consumers +------------------------- + +Once the confiuration is complete, the ``'live'`` attribute must be set to 1 in +order to instantiate the consumer. It can be set back to 0 to destroy the +virtual device. 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. + +Device-tree +----------- + +Virtual GPIO consumers can also be defined in device-tree. The compatible string +must be: ``"gpio-virtuser"`` with at least one property following the +standardized GPIO pattern. + +An example device-tree code defining a virtual GPIO consumer: + +.. code-block :: none + + gpio-virt-consumer { + compatible = "gpio-virtuser"; + + foo-gpios = <&gpio0 5 GPIO_ACTIVE_LOW>, <&gpio1 2 0>; + bar-gpios = <&gpio0 6 0>; + }; + +Controlling virtual GPIO consumers +---------------------------------- + +Once active, the device will export debugfs attributes for controlling GPIO +arrays as well as each requested GPIO line separately. Let's consider the +following device property: ``foo-gpios = <&gpio0 0 0>, <&gpio0 4 0>;``. + +The following debugfs attribute groups will be created: + +**Group:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo/`` + +This is the group that will contain the attributes for the entire GPIO array. + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo/values`` + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo/values_atomic`` + +Both attributes allow to read and set arrays of GPIO values. User must pass +exactly the number of values that the array contains in the form of a string +containing zeroes and ones representing inactive and active GPIO states +respectively. In this example: ``echo 11 > values``. + +The ``values_atomic`` attribute works the same as ``values`` but the kernel +will execute the GPIO driver callbacks in interrupt context. + +**Group:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/`` + +This is a group that represents a single GPIO with ``$index`` being its offset +in the array. + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/consumer`` + +Allows to set and read the consumer label of the GPIO line. + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/debounce`` + +Allows to set and read the debounce period of the GPIO line. + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/direction`` + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/direction_atomic`` + +These two attributes allow to set the direction of the GPIO line. They accept +"input" and "output" as values. The atomic variant executes the driver callback +in interrupt context. + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/interrupts`` + +If the line is requested in input mode, writing ``1`` to this attribute will +make the module listen for edge interrupts on the GPIO. Writing ``0`` disables +the monitoring. Reading this attribute returns the current number of registered +interrupts (both edges). + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/value`` + +**Attribute:** ``/sys/kernel/debug/gpio-virtuser/$dev_name/gpiod:foo:$index/value_atomic`` + +Both attributes allow to read and set values of individual requested GPIO lines. +They accept the following values: ``1`` and ``0``. |