dt-bindings: mtd: Document use of nvmem-cells compatible

Document nvmem-cells compatible used to treat mtd partitions as a
nvmem provider.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210312062830.20548-3-ansuelsmth@gmail.com

Documentation/devicetree/bindings/mtd/partitions/nvmem-cells.yaml

@@ -0,0 +1,99 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mtd/partitions/nvmem-cells.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nvmem cells
+
+description: |
+  Any partition containing the compatible "nvmem-cells" will register as a
+  nvmem provider.
+  Each direct subnodes represents a nvmem cell following the nvmem binding.
+  Nvmem binding to declare nvmem-cells can be found in:
+  Documentation/devicetree/bindings/nvmem/nvmem.yaml
+
+maintainers:
+  - Ansuel Smith <ansuelsmth@gmail.com>
+
+allOf:
+  - $ref: /schemas/nvmem/nvmem.yaml#
+
+properties:
+  compatible:
+    const: nvmem-cells
+
+required:
+  - compatible
+
+additionalProperties: true
+
+examples:
+  - |
+    partitions {
+      compatible = "fixed-partitions";
+      #address-cells = <1>;
+      #size-cells = <1>;
+
+      /* ... */
+
+      };
+      art: art@1200000 {
+        compatible = "nvmem-cells";
+        reg = <0x1200000 0x0140000>;
+        label = "art";
+        read-only;
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        macaddr_gmac1: macaddr_gmac1@0 {
+          reg = <0x0 0x6>;
+        };
+
+        macaddr_gmac2: macaddr_gmac2@6 {
+          reg = <0x6 0x6>;
+        };
+
+        pre_cal_24g: pre_cal_24g@1000 {
+          reg = <0x1000 0x2f20>;
+        };
+
+        pre_cal_5g: pre_cal_5g@5000{
+          reg = <0x5000 0x2f20>;
+        };
+      };
+  - |
+    partitions {
+        compatible = "fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+
+        partition@0 {
+            label = "bootloader";
+            reg = <0x000000 0x100000>;
+            read-only;
+        };
+
+        firmware@100000 {
+            compatible = "brcm,trx";
+            label = "firmware";
+            reg = <0x100000 0xe00000>;
+        };
+
+        calibration@f00000 {
+            compatible = "nvmem-cells";
+            label = "calibration";
+            reg = <0xf00000 0x100000>;
+            ranges = <0 0xf00000 0x100000>;
+            #address-cells = <1>;
+            #size-cells = <1>;
+
+            wifi0@0 {
+                reg = <0x000000 0x080000>;
+            };
+
+            wifi1@80000 {
+                reg = <0x080000 0x080000>;
+            };
+        };
+    };