@@ -69,6 +69,113 @@ write-only attribute files in sysfs.
$ echo gpio-aggregator.0 > delete_device
+Aggregating GPIOs using Configfs
+--------------------------------
+
+**Group:** ``/config/gpio-aggregator``
+
+ This is the root directory of the gpio-aggregator configfs tree.
+
+**Group:** ``/config/gpio-aggregator/<example-name>``
+
+ This directory represents a GPIO aggregator device. You can assign any
+ name to ``<example-name>`` (e.g. ``agg0``), except names starting with
+ ``_sysfs`` prefix, which are reserved for auto-generated configfs
+ entries corresponding to devices created via Sysfs.
+
+**Attribute:** ``/config/gpio-aggregator/<example-name>/live``
+
+ The ``live`` attribute allows to trigger the actual creation of the device
+ once it's fully configured. Accepted values are:
+
+ * ``1``, ``yes``, ``true`` : enable the virtual device
+ * ``0``, ``no``, ``false`` : disable the virtual device
+
+**Attribute:** ``/config/gpio-aggregator/<example-name>/dev_name``
+
+ The read-only ``dev_name`` attribute exposes the name of the device as it
+ will appear in the system on the platform bus (e.g. ``gpio-aggregator.0``).
+ This is useful for identifying a character device for the newly created
+ aggregator. If it's ``gpio-aggregator.0``,
+ ``/sys/devices/platform/gpio-aggregator.0/gpiochipX`` path tells you that the
+ GPIO device id is ``X``.
+
+You must create subdirectories for each virtual line you want to
+instantiate, named exactly as ``line0``, ``line1``, ..., ``lineY``, when
+you want to instantiate ``Y+1`` (Y >= 0) lines. Configure all lines before
+activating the device by setting ``live`` to 1.
+
+**Group:** ``/config/gpio-aggregator/<example-name>/<lineY>/``
+
+ This directory represents a GPIO line to include in the aggregator.
+
+**Attribute:** ``/config/gpio-aggregator/<example-name>/<lineY>/key``
+
+**Attribute:** ``/config/gpio-aggregator/<example-name>/<lineY>/offset``
+
+ The default values after creating the ``<lineY>`` directory are:
+
+ * ``key`` : <empty>
+ * ``offset`` : -1
+
+ ``key`` must always be explicitly configured, while ``offset`` depends.
+ Two configuration patterns exist for each ``<lineY>``:
+
+ (a). For lookup by GPIO line name:
+
+ * Set ``key`` to the line name.
+ * Ensure ``offset`` remains -1 (the default).
+
+ (b). For lookup by GPIO chip name and the line offset within the chip:
+
+ * Set ``key`` to the chip name.
+ * Set ``offset`` to the line offset (0 <= ``offset`` < 65535).
+
+**Attribute:** ``/config/gpio-aggregator/<example-name>/<lineY>/name``
+
+ The ``name`` attribute sets a custom name for lineY. If left unset, the
+ line will remain unnamed.
+
+Once the configuration is done, the ``'live'`` attribute must be set to 1
+in order to instantiate the aggregator device. It can be set back to 0 to
+destroy the virtual device. The module will synchronously wait for the new
+aggregator device to be successfully probed and if this doesn't happen, writing
+to ``'live'`` will result in an error. This is a different behaviour from the
+case when you create it using sysfs ``new_device`` interface.
+
+.. note::
+
+ For aggregators created via Sysfs, the configfs entries are
+ auto-generated and appear as ``/config/gpio-aggregator/_sysfs.<N>/``. You
+ cannot add or remove line directories with mkdir(2)/rmdir(2). To modify
+ lines, you must use the "delete_device" interface to tear down the
+ existing device and reconfigure it from scratch. However, you can still
+ toggle the aggregator with the ``live`` attribute and adjust the
+ ``key``, ``offset``, and ``name`` attributes for each line when ``live``
+ is set to 0 by hand (i.e. it's not waiting for deferred probe).
+
+Sample configuration commands
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. code-block:: sh
+
+ # Create a directory for an aggregator device
+ $ mkdir /sys/kernel/config/gpio-aggregator/agg0
+
+ # Configure each line
+ $ mkdir /sys/kernel/config/gpio-aggregator/agg0/line0
+ $ echo gpiochip0 > /sys/kernel/config/gpio-aggregator/agg0/line0/key
+ $ echo 6 > /sys/kernel/config/gpio-aggregator/agg0/line0/offset
+ $ echo test0 > /sys/kernel/config/gpio-aggregator/agg0/line0/name
+ $ mkdir /sys/kernel/config/gpio-aggregator/agg0/line1
+ $ echo gpiochip0 > /sys/kernel/config/gpio-aggregator/agg0/line1/key
+ $ echo 7 > /sys/kernel/config/gpio-aggregator/agg0/line1/offset
+ $ echo test1 > /sys/kernel/config/gpio-aggregator/agg0/line1/name
+
+ # Activate the aggregator device
+ $ echo 1 > /sys/kernel/config/gpio-aggregator/agg0/live
+
+
Generic GPIO Driver
-------------------
Add documentation for the newly added configfs-based interface for GPIO aggregator. Signed-off-by: Koichiro Den <koichiro.den@canonical.com> --- .../admin-guide/gpio/gpio-aggregator.rst | 107 ++++++++++++++++++ 1 file changed, 107 insertions(+)