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/u-boot,env.yaml

@@ -0,0 +1,132 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/nvmem/layouts/u-boot,env.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: U-Boot environment variables layout
+
+description: |
+  U-Boot uses environment variables to store device parameters and
+  configuration. They may be used for booting process, setup or keeping end user
+  info.
+
+  Data is stored using U-Boot specific formats (variant specific header and NUL
+  separated key-value pairs).
+
+  Environment data can be stored on various storage entities, e.g.:
+  1. Raw flash partition
+  2. UBI volume
+
+  This binding allows marking storage device (as containing env data) and
+  specifying used format.
+
+  Variables can be defined as NVMEM device subnodes.
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+properties:
+  compatible:
+    oneOf:
+      - description: A standalone env data block
+        const: u-boot,env
+      - description: Two redundant blocks with active one flagged
+        const: u-boot,env-redundant-bool
+      - description: Two redundant blocks with active having higher counter
+        const: u-boot,env-redundant-count
+      - description: Broadcom's variant with custom header
+        const: brcm,env
+
+  reg:
+    description: Partition offset and size for env on top of MTD
+    maxItems: 1
+
+  bootcmd:
+    type: object
+    description: Command to use for automatic booting
+
+  ethaddr:
+    type: object
+    description: Ethernet interfaces base MAC address.
+    additionalProperties: false
+
+    properties:
+      "#nvmem-cell-cells":
+        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:
+  - |
+    partitions {
+        compatible = "fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+            reg = <0x0 0x40000>;
+            label = "u-boot";
+            read-only;
+        };
+
+        env: partition@40000 {
+            compatible = "u-boot,env";
+            reg = <0x40000 0x10000>;
+
+            mac: ethaddr {
+                #nvmem-cell-cells = <1>;
+            };
+        };
+    };
+  - |
+    partitions {
+        compatible = "fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+            reg = <0x0 0x100000>;
+            compatible = "brcm,u-boot";
+            label = "u-boot";
+
+            partition-u-boot-env {
+                compatible = "brcm,env";
+
+                ethaddr {
+                };
+            };
+        };
+    };
+  - |
+    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>;
+                    };
+                };
+            };
+        };
+    };