dt-bindings: nvmem: convert U-Boot env to a layout

U-Boot environment variables can be stored in various data sources. MTD
is just one of available options. Refactor DT binding into a layout so
it can be used with UBI volumes and other NVMEM devices.

Link: https://lore.kernel.org/all/20231221173421.13737-1-zajec5@gmail.com/
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20240902142952.71639-4-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/nvmem/layouts/nvmem-layout.yaml

@@ -21,6 +21,7 @@ oneOf:
   - $ref: fixed-layout.yaml
   - $ref: kontron,sl28-vpd.yaml
   - $ref: onie,tlv-layout.yaml
+  - $ref: u-boot,env.yaml
 
 properties:
   compatible: true

Documentation/devicetree/bindings/nvmem/layouts/u-boot,env.yaml

@@ -1,10 +1,10 @@
 # SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
 %YAML 1.2
 ---
-$id: http://devicetree.org/schemas/nvmem/u-boot,env.yaml#
+$id: http://devicetree.org/schemas/nvmem/layouts/u-boot,env.yaml#
 $schema: http://devicetree.org/meta-schemas/core.yaml#
 
-title: U-Boot environment variables
+title: U-Boot environment variables layout
 
 description: |
   U-Boot uses environment variables to store device parameters and
@@ -21,9 +21,6 @@ description: |
   This binding allows marking storage device (as containing env data) and
   specifying used format.
 
-  Right now only flash partition case is covered but it may be extended to e.g.
-  UBI volumes in the future.
-
   Variables can be defined as NVMEM device subnodes.
 
 maintainers:
@@ -42,6 +39,7 @@ properties:
         const: brcm,env
 
   reg:
+    description: Partition offset and size for env on top of MTD
     maxItems: 1
 
   bootcmd:
@@ -58,6 +56,17 @@ properties:
         description: The first argument is a MAC address offset.
         const: 1
 
+allOf:
+  - if:
+      properties:
+        $nodename:
+          not:
+            contains:
+              pattern: "^partition@[0-9a-f]+$"
+    then:
+      properties:
+        reg: false
+
 additionalProperties: false
 
 examples:
@@ -101,3 +110,23 @@ examples:
             };
         };
     };
+  - |
+    partition@0 {
+        reg = <0x0 0x100000>;
+        label = "ubi";
+        compatible = "linux,ubi";
+
+        volumes {
+            ubi-volume-u-boot-env {
+                volname = "env";
+
+                nvmem-layout {
+                    compatible = "u-boot,env";
+
+                    ethaddr {
+                        #nvmem-cell-cells = <1>;
+                    };
+                };
+            };
+        };
+    };