[RFC PATCH 1/2] dt-bindings: mtd: Add bindings for describing concatinated MTD devices

[Amit Kumar Mahapatra]

This approach was suggested by Rob [1] during a discussion on Miquel's
initial approach [2] to extend the MTD-CONCAT driver to support stacked
memories.
Define each flash node separately with its respective partitions, and add
a 'concat-parts' binding to link the partitions of the two flash nodes that
need to be concatenated.

flash at 0 {
        compatible = "jedec,spi-nor"
        ...
                partitions {
                compatible = "fixed-partitions";
                        concat-partition = <&flash0_partition &flash1_partition>;
                        flash0_partition: partition at 0 {
                                label = "part0_0";
                                reg = <0x0 0x800000>;
                        }
                }
}
flash at 1 {
        compatible = "jedec,spi-nor"
        ...
                partitions {
                compatible = "fixed-partitions";
                        concat-partition = <&flash0_partition &flash1_partition>;
                        flash1_partition: partition at 0 {
                                label = "part0_1";
                                reg = <0x0 0x800000>;
                        }
                }
}

Based on the bindings the MTD-CONCAT driver need to be updated to create
virtual mtd-concat devices.

[1] https://lore.kernel.org/all/20191118221341.GA30937@bogus/
[2] https://lore.kernel.org/all/20191113171505.26128-4-miquel.raynal@bootlin.com/

Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra at amd.com>
---
 .../mtd/partitions/fixed-partitions.yaml       | 18 ++++++++++++++++++
 .../bindings/mtd/partitions/partitions.yaml    |  6 ++++++
 2 files changed, 24 insertions(+)

diff --git a/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
index 058253d6d889..df4ccb3dfeba 100644
--- a/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
+++ b/Documentation/devicetree/bindings/mtd/partitions/fixed-partitions.yaml
@@ -183,3 +183,21 @@ examples:
             read-only;
         };
     };
+
+  - |
+    partitions {
+        compatible = "fixed-partitions";
+        #address-cells = <1>;
+        #size-cells = <1>;
+        concat-parts = <&part0 &part1>;
+
+        part0: partition at 0 {
+            label = "flash0-part0";
+            reg = <0x0000000 0x100000>;
+        };
+
+        part1: partition at 100000 {
+            label = "flash1-part0";
+            reg = <0x0100000 0x200000>;
+        };
+    };
diff --git a/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml b/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
index 1dda2c80747b..86bbd83c3f6d 100644
--- a/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
+++ b/Documentation/devicetree/bindings/mtd/partitions/partitions.yaml
@@ -32,6 +32,12 @@ properties:
   '#size-cells':
     enum: [1, 2]
 
+  concat-parts:
+    description: List of MTD partitions phandles that should be concatenated.
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    minItems: 2
+    maxItems: 4
+
 patternProperties:
   "^partition(-.+|@[0-9a-f]+)$":
     $ref: partition.yaml
-- 
2.34.1