dt-bindings: power: mt8196-gpufreq: Describe nvmem provider ability

On the MediaTek MT8196 SoC, the Mali GPU's "shader_present" hardware
register may also include a non-functional shader core, along with the
present shader cores. An efuse elsewhere in the SoC provides the
shader_present mask with the fused off core omitted.

However, the efuse address is not publicly disclosed. What is known
though is that the GPUEB MCU reads this efuse, and exposes its contents
in the memory it shares with the application processor.

We can therefore describe the mediatek,mt8196-gpufreq device as being an
nvmem provider for this purpose, as it does provide nvmem access in an
indirect way.

The shader-present child node is left out of the list of required
properties as we may one day be able to describe the actual efuse region
this value comes from, so the gpufreq device isn't necessarily the only
device that can provide this cell, and implementations shouldn't need to
implement this functionality once this is the case.

Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/power/mediatek,mt8196-gpufreq.yaml

@@ -74,9 +74,18 @@ properties:
   "#clock-cells":
     const: 1
 
+  "#nvmem-cell-cells":
+    const: 0
+
   "#power-domain-cells":
     const: 0
 
+  shader-present:
+    type: object
+
+dependencies:
+  shader-present: [ "#nvmem-cell-cells" ]
+
 required:
   - compatible
   - reg
@@ -113,5 +122,9 @@ examples:
                      "ccf", "fast-dvfs";
         memory-region = <&gpueb_shared_memory>;
         #clock-cells = <1>;
+        #nvmem-cell-cells = <0>;
         #power-domain-cells = <0>;
+
+        shader-present {
+        };
     };