docs: Add/Update state documentation

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

1 files changed, 46 insertions, 0 deletions

diff --git a/Documentation/user/state.rst b/Documentation/user/state.rst
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+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.