dt-bindings: virtio: Add binding for virtio devices

Allow virtio device sub-nodes to be added to the virtio mmio or pci
nodes. The compatible property for virtio device must be of the format
"virtio,device<ID>", where ID is virtio device ID in hexadecimal format.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://lore.kernel.org/r/d8319fd18df7086b12cdcc23193c313893aa071a.1627362340.git.viresh.kumar@linaro.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/virtio/mmio.yaml

@@ -36,7 +36,8 @@ required:
   - reg
   - interrupts
 
-additionalProperties: false
+additionalProperties:
+  type: object
 
 examples:
   - |

Documentation/devicetree/bindings/virtio/virtio-device.yaml

@@ -0,0 +1,41 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/virtio/virtio-device.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Virtio device bindings
+
+maintainers:
+  - Viresh Kumar <viresh.kumar@linaro.org>
+
+description:
+  These bindings are applicable to virtio devices irrespective of the bus they
+  are bound to, like mmio or pci.
+
+# We need a select here so we don't match all nodes with 'virtio,mmio'
+properties:
+  compatible:
+    pattern: "^virtio,device[0-9a-f]{1,8}$"
+    description: Virtio device nodes.
+      "virtio,deviceID", where ID is the virtio device id. The textual
+      representation of ID shall be in lower case hexadecimal with leading
+      zeroes suppressed.
+
+required:
+  - compatible
+
+additionalProperties: true
+
+examples:
+  - |
+    virtio@3000 {
+        compatible = "virtio,mmio";
+        reg = <0x3000 0x100>;
+        interrupts = <43>;
+
+        i2c {
+            compatible = "virtio,device22";
+        };
+    };
+...