dt-bindings: PCI: dwc: Apply generic schema for generic device only

Having the generic compatible strings constraints with the 'any'+'generic
string' semantic implicitly encourages either to add new DW PCIe-based
DT-bindings with the generic compatible string attached or just forget
about adding new DT-bindings since the corresponding DT-node will be
evaluated anyway. Moreover having that semantic implemented in the
generic DT-schema causes the DT-validation tool to apply the schema twice:
first by implicit compatible-string-based selection and second by means of
the 'allOf: [ $ref ]' statement. Let's fix all of that by dropping the
compatible property constraints and selecting the generic DT-schema only
for the purely generic DW PCIe DT-nodes. The later is required since there
is a driver for such devices. (Though there are no such DT-nodes currently
defined in the kernel DT sources.)

Link: https://lore.kernel.org/r/20221113191301.5526-8-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/pci/snps,dw-pcie-ep.yaml

@@ -13,16 +13,20 @@ maintainers:
 description: |
   Synopsys DesignWare PCIe host controller endpoint
 
+# Please create a separate DT-schema for your DWC PCIe Endpoint controller
+# and make sure it's assigned with the vendor-specific compatible string.
+select:
+  properties:
+    compatible:
+      const: snps,dw-pcie-ep
+  required:
+    - compatible
+
 allOf:
   - $ref: /schemas/pci/pci-ep.yaml#
   - $ref: /schemas/pci/snps,dw-pcie-common.yaml#
 
 properties:
-  compatible:
-    anyOf:
-      - {}
-      - const: snps,dw-pcie-ep
-
   reg:
     description: |
       It should contain Data Bus Interface (dbi) and config registers for all
@@ -38,9 +42,9 @@ properties:
       enum: [dbi, dbi2, config, atu, addr_space, link, atu_dma, appl]
 
 required:
+  - compatible
   - reg
   - reg-names
-  - compatible
 
 additionalProperties: true
 

Documentation/devicetree/bindings/pci/snps,dw-pcie.yaml

@@ -13,16 +13,20 @@ maintainers:
 description: |
   Synopsys DesignWare PCIe host controller
 
+# Please create a separate DT-schema for your DWC PCIe Root Port controller
+# and make sure it's assigned with the vendor-specific compatible string.
+select:
+  properties:
+    compatible:
+      const: snps,dw-pcie
+  required:
+    - compatible
+
 allOf:
   - $ref: /schemas/pci/pci-bus.yaml#
   - $ref: /schemas/pci/snps,dw-pcie-common.yaml#
 
 properties:
-  compatible:
-    anyOf:
-      - {}
-      - const: snps,dw-pcie
-
   reg:
     description: |
       It should contain Data Bus Interface (dbi) and config registers for all
@@ -47,9 +51,9 @@ properties:
 additionalProperties: true
 
 required:
+  - compatible
   - reg
   - reg-names
-  - compatible
 
 examples:
   - |