linux-kernel - [PATCH 3/4] arm64/fp: Clarify effect of setting an unsupported system VL

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Message-Id: <20240122-arm64-sve-sme-doc-v1-3-3d492e45265b@kernel.org>
Date: Mon, 22 Jan 2024 20:41:53 +0000
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>, Jonathan Corbet <corbet@....net>
Cc: Dave Martin <dave.martin@....com>, linux-arm-kernel@...ts.infradead.org, 
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>, 
 Edmund Grimley-Evans <edmund.grimley-evans@....com>
Subject: [PATCH 3/4] arm64/fp: Clarify effect of setting an unsupported
 system VL

The documentation for system vector length configuration does not cover all
cases where unsupported values are written, tighten it up.

Reported-by: Edmund Grimley-Evans <edmund.grimley-evans@....com>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 Documentation/arch/arm64/sme.rst | 5 ++---
 Documentation/arch/arm64/sve.rst | 5 ++---
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/Documentation/arch/arm64/sme.rst b/Documentation/arch/arm64/sme.rst
index 3133d0e91b48..ba0a5e5b2523 100644
--- a/Documentation/arch/arm64/sme.rst
+++ b/Documentation/arch/arm64/sme.rst
@@ -379,9 +379,8 @@ The regset data starts with struct user_za_header, containing:
 /proc/sys/abi/sme_default_vector_length
 
     Writing the text representation of an integer to this file sets the system
-    default vector length to the specified value, unless the value is greater
-    than the maximum vector length supported by the system in which case the
-    default vector length is set to that maximum.
+    default vector length to the specified value rounded to a supported value
+    using the same rules as for setting vector length via prctl().
 
     The result can be determined by reopening the file and reading its
     contents.
diff --git a/Documentation/arch/arm64/sve.rst b/Documentation/arch/arm64/sve.rst
index b45a2da19bf1..b923727ff4b9 100644
--- a/Documentation/arch/arm64/sve.rst
+++ b/Documentation/arch/arm64/sve.rst
@@ -423,9 +423,8 @@ The regset data starts with struct user_sve_header, containing:
 /proc/sys/abi/sve_default_vector_length
 
     Writing the text representation of an integer to this file sets the system
-    default vector length to the specified value, unless the value is greater
-    than the maximum vector length supported by the system in which case the
-    default vector length is set to that maximum.
+    default vector length to the specified value rounded to a supported value
+    using the same rules as for setting vector length via prctl().
 
     The result can be determined by reopening the file and reading its
     contents.

-- 
2.30.2