misc: Add a driver to expose U-Boot environment variable data

Add a driver to expose U-Boot environment variable data as a single
mmap-able device, hiding various low-level details such as:

    * Preamble format differences
    * Read/write logic in presence of redundant partition

Not very useful on its own, it is a crucial low-level plumbing needed
by filesystem driver introduced in the following commit.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Cory Tusar <cory.tusar@zii.aero>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 43 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/barebox/barebox,uboot-environment.rst b/Documentation/devicetree/bindings/barebox/barebox,uboot-environment.rst
new file mode 100644
index 0000000000..da0ccd2c25
--- /dev/null
+++ b/Documentation/devicetree/bindings/barebox/barebox,uboot-environment.rst
@@ -0,0 +1,43 @@
+U-Boot environment device
+=========================
+
+This driver provides a unified device exposing U-Boot environment
+varaible data, sans the low-level parts. Resulting device is intended
+to be used with corresponding filesystem driver to expose environment
+data as a filesystem.
+
+Required properties:
+
+* ``compatible``: should be ``barebox,uboot-environment``
+* ``device-path``: phandle of the partition the device environment is
+  on (single partiton configuration)
+* ``device-path-0`` and ``device-path-1``: phandle of the partition
+  the environment is on (redundant configuration)
+
+Example:
+
+.. code-block:: none
+
+  environment {
+  	compatible = "barebox,uboot-environment";
+	device-path-0 = &uboot_env_0;
+	device-path-1 = &uboot_env_1;
+  };
+  
+  &usdhc4 {
+	partitions {
+		compatible = "fixed-partitions";
+		#address-cells = <1>;
+		#size-cells = <1>;
+
+		uboot_env_0: partition@c0000 {
+			label = "uboot-environment-0";
+			reg = <0xc0000 0x4000>;
+		};
+
+		uboot_env_1: partition@cc800 {
+			label = "uboot-environment-1";
+			reg = <0xcc800 0x4000>;
+		};
+	};
+  };