Add a property analogous to the vlenb CSR so that software can detect
the vector length of each CPU prior to it being brought online.
Currently software has to assume that the vector length read from the
boot CPU applies to all possible CPUs. On T-Head CPUs implementing
pre-ratification vector, reading the th.vlenb CSR may produce an illegal
instruction trap, so this property is required on such systems.

Signed-off-by: Charlie Jenkins <redacted>
---
 Documentation/devicetree/bindings/riscv/thead.yaml | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/thead.yaml b/Documentation/devicetree/bindings/riscv/thead.yaml
index 301912dcd290..5e578df36ac5 100644
--- a/Documentation/devicetree/bindings/riscv/thead.yaml
+++ b/Documentation/devicetree/bindings/riscv/thead.yaml

@@ -28,6 +28,13 @@ properties:
           - const: sipeed,lichee-module-4a
           - const: thead,th1520
 
+thead,vlenb:
+  $ref: /schemas/types.yaml#/definitions/uint32
+  description:
+    VLEN/8, the vector register length in bytes. This property is required in
+    systems where the vector register length is not identical on all harts, or
+    the vlenb CSR is not available.
+
 additionalProperties: true
 
 ...

-- 
2.44.0