linux-kernel - [PATCH v8 02/13] dt-bindings: cpus: add a thead vlen register length property

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Message-Id: <20240724-xtheadvector-v8-2-cf043168e137@rivosinc.com>
Date: Wed, 24 Jul 2024 21:16:19 -0700
From: Charlie Jenkins <charlie@...osinc.com>
To: Conor Dooley <conor@...nel.org>, Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Jisheng Zhang <jszhang@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
 Jernej Skrabec <jernej.skrabec@...il.com>, 
 Samuel Holland <samuel@...lland.org>, 
 Samuel Holland <samuel.holland@...ive.com>, 
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>, 
 Guo Ren <guoren@...nel.org>, Evan Green <evan@...osinc.com>, 
 Andy Chiu <andy.chiu@...ive.com>, Jessica Clarke <jrtc27@...c27.com>, 
 Andrew Jones <ajones@...tanamicro.com>
Cc: linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org, 
 linux-kernel@...r.kernel.org, linux-sunxi@...ts.linux.dev, 
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>, 
 Conor Dooley <conor.dooley@...rochip.com>
Subject: [PATCH v8 02/13] dt-bindings: cpus: add a thead vlen register
 length property

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 <charlie@...osinc.com>
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
---
 Documentation/devicetree/bindings/riscv/cpus.yaml | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

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

-- 
2.44.0