dt-bindings: mtd: Document nand-ecc-placement

This optional property defines where the ECC bytes are expected to be
stored. No value defaults to an unknown location, while these
locations can be explicitly set to OOB or interleaved depending if
the ECC bytes are entirely stored in the OOB area or mixed with
regular data in the main area (also sometimes referred as
"syndrome").

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20200827085208.16276-6-miquel.raynal@bootlin.com

Documentation/devicetree/bindings/mtd/nand-controller.yaml

@@ -55,6 +55,16 @@ patternProperties:
         $ref: /schemas/types.yaml#/definitions/string
         enum: [none, soft, hw, hw_syndrome, hw_oob_first, on-die]
 
+      nand-ecc-placement:
+        allOf:
+          - $ref: /schemas/types.yaml#/definitions/string
+          - enum: [ oob, interleaved ]
+        description:
+          Location of the ECC bytes. This location is unknown by default
+          but can be explicitly set to "oob", if all ECC bytes are
+          known to be stored in the OOB area, or "interleaved" if ECC
+          bytes will be interleaved with regular data in the main area.
+
       nand-ecc-algo:
         description:
           Desired ECC algorithm.