docs: Add/Update state documentation

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

Documentation/devicetree/bindings/barebox/barebox,state.rst

@@ -36,7 +36,12 @@ Optional properties:
 
 * ``algo``: A HMAC algorithm used to detect manipulation of the data
   or header, sensible values follow this pattern ``hmac(<HASH>)``,
-  e.g. ``hmac(sha256)``.
+  e.g. ``hmac(sha256)``. Only used for ``raw``.
+* ``backend-stridesize``: Maximum size per copy of the data. Only important for
+  non-MTD devices
+* ``backend-storage-type``: Type of the storage. This has two options at the
+  moment. For MTD with erasing the correct type is ``circular``. For all other
+  devices and files, ``direct`` is the needed type.
 
 Variable nodes
 --------------

Documentation/user/state.rst

@@ -0,0 +1,46 @@
+Barebox State Framework
+=======================
+
+The state framework is build to exchange data between Barebox and Linux
+userspace using a non-volatile storage. There are several components involved.
+Barebox has a state driver to access the variables. For the Linux Userspace
+there is a userspace tool.
+
+Devicetree
+----------
+
+Currently the devicetree defines the layout of the variables and data.
+Variables are fixed size. Several types are supported, see the binding
+documentation for details.
+
+Data Formats
+------------
+
+The state data can be stored in different ways. Currently two formats are
+available, ``raw`` and ``dtb``. Both format the state data differently.
+Basically these are serializers. The raw serializer additionally supports a
+HMAC algorithm to detect manipulations.
+
+Storage Backends
+----------------
+
+The serialized data can be stored to different backends which are automatically
+selected depending on the defined backend in the devicetree. Currently two
+implementations exist, ``circular`` and ``direct``. ``circular`` writes the
+data sequentially on the backend storage device. Each save is appended until
+the storage area is full. It then erases the block and starts from offset 0.
+``circular`` is used for MTD devices with erase functionality. ``direct``
+writes the data directly to the file without erasing.
+
+For all backends multiple copies are written to handle read errors.
+
+Commands
+--------
+
+The ``state`` command can be used to store and manipulate the state. Using
+``state`` without argument lists you all available states with their name.
+``devinfo STATE_NAME`` shows you all variables and their values. ``state -s``
+stores the state.
+
+Starting Barebox will automatically load the last written state. If loading the
+state fails the defaults are used.

Documentation/user/user-manual.rst

@@ -31,6 +31,7 @@ Contents:
    system-setup
    reset-reason
    system-reset
+   state
 
 * :ref:`search`
 * :ref:`genindex`