gpio: sim: new testing module

.. 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

	  These virtual GPIOs can be routed to real GPIOs or attached to

	  simulators on the host (like QEMU).

config GPIO_SIM

	tristate "GPIO Simulator Module"

	select IRQ_SIM

	select CONFIGFS_FS

	help

	  This enables the GPIO simulator - a configfs-based GPIO testing

	  driver.

endmenu

endif

obj-$(CONFIG_GPIO_SCH311X)		+= gpio-sch311x.o

obj-$(CONFIG_GPIO_SCH)			+= gpio-sch.o

obj-$(CONFIG_GPIO_SIFIVE)		+= gpio-sifive.o

obj-$(CONFIG_GPIO_SIM)			+= gpio-sim.o

obj-$(CONFIG_GPIO_SIOX)			+= gpio-siox.o

obj-$(CONFIG_GPIO_SL28CPLD)		+= gpio-sl28cpld.o

obj-$(CONFIG_GPIO_SODAVILLE)		+= gpio-sodaville.o