diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
index 8edc8261241a..c0cf6cf56749 100644
--- a/Documentation/devicetree/bindings/riscv/cpus.yaml
+++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
@@ -26,6 +26,18 @@ description: |
 allOf:
   - $ref: /schemas/cpu.yaml#
   - $ref: extensions.yaml
+  - if:
+      not:
+        properties:
+          compatible:
+            contains:
+              enum:
+                - thead,c906
+                - thead,c910
+                - thead,c920
+    then:
+      properties:
+        thead,vlenb: false
 
 properties:
   compatible:
@@ -95,6 +107,13 @@ properties:
     description:
       The blocksize in bytes for the Zicboz cache operations.
 
+  thead,vlenb:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      VLEN/8, the vector register length in bytes. This property is required on
+      thead systems where the vector register length is not identical on all harts, or
+      the vlenb CSR is not available.
+
   # RISC-V has multiple properties for cache op block sizes as the sizes
   # differ between individual CBO extensions
   cache-op-block-size: false