dt-bindings: soc: smem: Make indirection optional

In the olden days the Qualcomm shared memory (SMEM) region consisted of
multiple chunks of memory, so SMEM was described as a standalone node
with references to its various memory regions.

But practically all modern Qualcomm platforms has a single reserved memory
region used for SMEM. So rather than having to use two nodes to describe
the one SMEM region, update the binding to allow the reserved-memory
region alone to describe SMEM.

The olden format is preserved as valid, as this is widely used already.
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>
Link: https://lore.kernel.org/r/20210930182111.57353-3-bjorn.andersson@linaro.org

Documentation/devicetree/bindings/soc/qcom/qcom,smem.yaml

@@ -10,14 +10,18 @@ maintainers:
   - Andy Gross <agross@kernel.org>
   - Bjorn Andersson <bjorn.andersson@linaro.org>
 
-description: |
-  This binding describes the Qualcomm Shared Memory Manager, used to share data
-  between various subsystems and OSes in Qualcomm platforms.
+description:
+  This binding describes the Qualcomm Shared Memory Manager, a region of
+  reserved-memory used to share data between various subsystems and OSes in
+  Qualcomm platforms.
 
 properties:
   compatible:
     const: qcom,smem
 
+  reg:
+    maxItems: 1
+
   memory-region:
     maxItems: 1
     description: handle to memory reservation for main SMEM memory region.
@@ -29,11 +33,19 @@ properties:
     $ref: /schemas/types.yaml#/definitions/phandle
     description: handle to RPM message memory resource
 
+  no-map: true
+
 required:
   - compatible
-  - memory-region
   - hwlocks
 
+oneOf:
+  - required:
+      - reg
+      - no-map
+  - required:
+      - memory-region
+
 additionalProperties: false
 
 examples:
@@ -43,6 +55,20 @@ examples:
         #size-cells = <1>;
         ranges;
 
+        smem@fa00000 {
+            compatible = "qcom,smem";
+            reg = <0xfa00000 0x200000>;
+            no-map;
+
+            hwlocks = <&tcsr_mutex 3>;
+        };
+    };
+  - |
+    reserved-memory {
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges;
+
         smem_region: smem@fa00000 {
             reg = <0xfa00000 0x200000>;
             no-map;