linux-kernel - [PATCH 1/2] dt-bindings: riscv: cpus: add a vlen register length property

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Message-Id: <20240515-add_vlenb_to_dt-v1-1-4ebd7cba0aa1@rivosinc.com>
Date: Wed, 15 May 2024 14:50:14 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Conor Dooley <conor@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>
Cc: Palmer Dabbelt <palmer@...ive.com>, linux-riscv@...ts.infradead.org, 
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>, 
 Conor Dooley <conor.dooley@...rochip.com>
Subject: [PATCH 1/2] dt-bindings: riscv: cpus: add a vlen register length
 property

From: Conor Dooley <conor.dooley@...rochip.com>

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: Conor Dooley <conor.dooley@...rochip.com>
Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
 Documentation/devicetree/bindings/riscv/cpus.yaml | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
index d87dd50f1a4b..edcb6a7d9319 100644
--- a/Documentation/devicetree/bindings/riscv/cpus.yaml
+++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
@@ -94,6 +94,12 @@ properties:
     description:
       The blocksize in bytes for the Zicboz cache operations.
 
+  riscv,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.
+
   # RISC-V has multiple properties for cache op block sizes as the sizes
   # differ between individual CBO extensions
   cache-op-block-size: false

-- 
2.44.0