112 lines
3.5 KiB
ReStructuredText
112 lines
3.5 KiB
ReStructuredText
|
.. SPDX-License-Identifier: GPL-2.0-only
|
||
|
|
|
||
|
|
GPIO Aggregator
|
||
|
|
===============
|
||
|
|
|
||
|
|
The GPIO Aggregator provides a mechanism to aggregate GPIOs, and expose them as
|
||
|
|
a new gpio_chip. This supports the following use cases.
|
||
|
|
|
||
|
|
|
||
|
|
Aggregating GPIOs using Sysfs
|
||
|
|
-----------------------------
|
||
|
|
|
||
|
|
GPIO controllers are exported to userspace using /dev/gpiochip* character
|
||
|
|
devices. Access control to these devices is provided by standard UNIX file
|
||
|
|
system permissions, on an all-or-nothing basis: either a GPIO controller is
|
||
|
|
accessible for a user, or it is not.
|
||
|
|
|
||
|
|
The GPIO Aggregator provides access control for a set of one or more GPIOs, by
|
||
|
|
aggregating them into a new gpio_chip, which can be assigned to a group or user
|
||
|
|
using standard UNIX file ownership and permissions. Furthermore, this
|
||
|
|
simplifies and hardens exporting GPIOs to a virtual machine, as the VM can just
|
||
|
|
grab the full GPIO controller, and no longer needs to care about which GPIOs to
|
||
|
|
grab and which not, reducing the attack surface.
|
||
|
|
|
||
|
|
Aggregated GPIO controllers are instantiated and destroyed by writing to
|
||
|
|
write-only attribute files in sysfs.
|
||
|
|
|
||
|
|
/sys/bus/platform/drivers/gpio-aggregator/
|
||
|
|
|
||
|
|
"new_device" ...
|
||
|
|
Userspace may ask the kernel to instantiate an aggregated GPIO
|
||
|
|
controller by writing a string describing the GPIOs to
|
||
|
|
aggregate to the "new_device" file, using the format
|
||
|
|
|
||
|
|
.. code-block:: none
|
||
|
|
|
||
|
|
[<gpioA>] [<gpiochipB> <offsets>] ...
|
||
|
|
|
||
|
|
Where:
|
||
|
|
|
||
|
|
"<gpioA>" ...
|
||
|
|
is a GPIO line name,
|
||
|
|
|
||
|
|
"<gpiochipB>" ...
|
||
|
|
is a GPIO chip label, and
|
||
|
|
|
||
|
|
"<offsets>" ...
|
||
|
|
is a comma-separated list of GPIO offsets and/or
|
||
|
|
GPIO offset ranges denoted by dashes.
|
||
|
|
|
||
|
|
Example: Instantiate a new GPIO aggregator by aggregating GPIO
|
||
|
|
line 19 of "e6052000.gpio" and GPIO lines 20-21 of
|
||
|
|
"e6050000.gpio" into a new gpio_chip:
|
||
|
|
|
||
|
|
.. code-block:: sh
|
||
|
|
|
||
|
|
$ echo 'e6052000.gpio 19 e6050000.gpio 20-21' > new_device
|
||
|
|
|
||
|
|
"delete_device" ...
|
||
|
|
Userspace may ask the kernel to destroy an aggregated GPIO
|
||
|
|
controller after use by writing its device name to the
|
||
|
|
"delete_device" file.
|
||
|
|
|
||
|
|
Example: Destroy the previously-created aggregated GPIO
|
||
|
|
controller, assumed to be "gpio-aggregator.0":
|
||
|
|
|
||
|
|
.. code-block:: sh
|
||
|
|
|
||
|
|
$ echo gpio-aggregator.0 > delete_device
|
||
|
|
|
||
|
|
|
||
|
|
Generic GPIO Driver
|
||
|
|
-------------------
|
||
|
|
|
||
|
|
The GPIO Aggregator can also be used as a generic driver for a simple
|
||
|
|
GPIO-operated device described in DT, without a dedicated in-kernel driver.
|
||
|
|
This is useful in industrial control, and is not unlike e.g. spidev, which
|
||
|
|
allows the user to communicate with an SPI device from userspace.
|
||
|
|
|
||
|
|
Binding a device to the GPIO Aggregator is performed either by modifying the
|
||
|
|
gpio-aggregator driver, or by writing to the "driver_override" file in Sysfs.
|
||
|
|
|
||
|
|
Example: If "door" is a GPIO-operated device described in DT, using its own
|
||
|
|
compatible value::
|
||
|
|
|
||
|
|
door {
|
||
|
|
compatible = "myvendor,mydoor";
|
||
|
|
|
||
|
|
gpios = <&gpio2 19 GPIO_ACTIVE_HIGH>,
|
||
|
|
<&gpio2 20 GPIO_ACTIVE_LOW>;
|
||
|
|
gpio-line-names = "open", "lock";
|
||
|
|
};
|
||
|
|
|
||
|
|
it can be bound to the GPIO Aggregator by either:
|
||
|
|
|
||
|
|
1. Adding its compatible value to ``gpio_aggregator_dt_ids[]``,
|
||
|
|
2. Binding manually using "driver_override":
|
||
|
|
|
||
|
|
.. code-block:: sh
|
||
|
|
|
||
|
|
$ echo gpio-aggregator > /sys/bus/platform/devices/door/driver_override
|
||
|
|
$ echo door > /sys/bus/platform/drivers/gpio-aggregator/bind
|
||
|
|
|
||
|
|
After that, a new gpiochip "door" has been created:
|
||
|
|
|
||
|
|
.. code-block:: sh
|
||
|
|
|
||
|
|
$ gpioinfo door
|
||
|
|
gpiochip12 - 2 lines:
|
||
|
|
line 0: "open" unused input active-high
|
||
|
|
line 1: "lock" unused input active-high
|