[PATCH V4] dt-bindings: nvmem: fixed-cell: add compatible for MAC cells

[Rafał Miłecki]

From: Rafał Miłecki <rafal at milecki.pl>

A lot of home routers have NVMEM fixed cells containing MAC address that
need some further processing. In ~99% cases MAC needs to be:
1. Optionally parsed from ASCII format
2. Increased by a vendor-picked value

There was already an attempt to design a binding for that at NVMEM
device level in the past. It wasn't accepted though as it didn't really
fit NVMEM device layer.

The introduction of NVMEM fixed-cells layout seems to be an opportunity
to provide a relevant binding in a clean way.

This commit adds a *generic* compatible string: "mac-base". As always it
needs to be carefully reviewed.

OpenWrt project currently supports ~300 home routers that have NVMEM
cell with binary-stored base MAC.T hose devices are manufactured by
multiple vendors. There are TP-Link devices (76 of them), Netgear (19),
D-Link (11), OpenMesh (9), EnGenius (8), GL.iNet (8), ZTE (7),
Xiaomi (5), Ubiquiti (6) and more. Those devices don't share an
architecture or SoC.

Another 200 devices have base MAC stored in an ASCII format (not all
those devices have been converted to DT though).

It would be impractical to provide unique "compatible" strings for NVMEM
layouts of all those devices. It seems like a valid case for allowing a
generic binding instead. Even if this binding will not be sufficient for
some further devices it seems to be useful enough as it is.

Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
---
V2: Drop "mac-ascii" as length can be checked instead
    Fix "allOf" by adding required: [ compatible ]
V3: Fix cell length in "description" (thank you Rob!)
V4: Fix cell length (12 → 6) in fixed-layout.yaml example as well
---
 .../bindings/nvmem/layouts/fixed-cell.yaml    | 26 +++++++++++++++++++
 .../bindings/nvmem/layouts/fixed-layout.yaml  | 12 +++++++++
 .../devicetree/bindings/nvmem/nvmem.yaml      |  5 +++-
 3 files changed, 42 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/nvmem/layouts/fixed-cell.yaml b/Documentation/devicetree/bindings/nvmem/layouts/fixed-cell.yaml
index e698098450e1..ac2381e66027 100644
--- a/Documentation/devicetree/bindings/nvmem/layouts/fixed-cell.yaml
+++ b/Documentation/devicetree/bindings/nvmem/layouts/fixed-cell.yaml
@@ -11,6 +11,15 @@ maintainers:
   - Srinivas Kandagatla <srinivas.kandagatla at linaro.org>
 
 properties:
+  compatible:
+    oneOf:
+      - const: mac-base
+        description: >
+          Cell with base MAC address to be used for calculating extra relative
+          addresses.
+          It can be stored in a plain binary format (cell length 6) or as an
+          ASCII text like "00:11:22:33:44:55" (cell length 17).
+
   reg:
     maxItems: 1
 
@@ -25,6 +34,23 @@ properties:
         description:
           Size in bit within the address range specified by reg.
 
+allOf:
+  - if:
+      required: [ compatible ]
+    then:
+      if:
+        properties:
+          compatible:
+            contains:
+              const: mac-base
+      then:
+        properties:
+          "#nvmem-cell-cells":
+            description: The first argument is a MAC address offset.
+            const: 1
+        required:
+          - "#nvmem-cell-cells"
+
 required:
   - reg
 
diff --git a/Documentation/devicetree/bindings/nvmem/layouts/fixed-layout.yaml b/Documentation/devicetree/bindings/nvmem/layouts/fixed-layout.yaml
index c271537d0714..9bd34bd5af30 100644
--- a/Documentation/devicetree/bindings/nvmem/layouts/fixed-layout.yaml
+++ b/Documentation/devicetree/bindings/nvmem/layouts/fixed-layout.yaml
@@ -44,6 +44,18 @@ examples:
         #address-cells = <1>;
         #size-cells = <1>;
 
+        mac at 100 {
+            compatible = "mac-base";
+            reg = <0x100 0x6>;
+            #nvmem-cell-cells = <1>;
+        };
+
+        mac at 110 {
+            compatible = "mac-base";
+            reg = <0x110 0x11>;
+            #nvmem-cell-cells = <1>;
+        };
+
         calibration at 4000 {
             reg = <0x4000 0x100>;
         };
diff --git a/Documentation/devicetree/bindings/nvmem/nvmem.yaml b/Documentation/devicetree/bindings/nvmem/nvmem.yaml
index 980244100690..9f921d940142 100644
--- a/Documentation/devicetree/bindings/nvmem/nvmem.yaml
+++ b/Documentation/devicetree/bindings/nvmem/nvmem.yaml
@@ -49,7 +49,10 @@ properties:
 patternProperties:
   "@[0-9a-f]+(,[0-7])?$":
     type: object
-    $ref: layouts/fixed-cell.yaml
+    allOf:
+      - $ref: layouts/fixed-cell.yaml
+      - properties:
+          compatible: false
     deprecated: true
 
 additionalProperties: true
-- 
2.35.3