linux-kernel - [PATCH] arm64/sve: Document that __SVE_VQ

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Message-Id: <20240206-arm64-sve-vl-max-comment-v1-1-dddf16414412@kernel.org>
Date: Tue, 06 Feb 2024 16:27:01 +0000
From: Mark Brown <broonie@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>, 
 Will Deacon <will@...nel.org>
Cc: Dave Martin <Dave.Martin@....com>, linux-arm-kernel@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>
Subject: [PATCH] arm64/sve: Document that __SVE_VQ_MAX is much larger than
 needed

__SVE_VQ_MAX is defined without comment as 512 but the actual
architectural maximum is 16, a substantial difference which might not
be obvious to readers especially given the several different units used
for specifying vector sizes in various contexts and the fact that it's
often used via macros.  In an effort to minimise surprises for users who
might assume the value is the architectural maximum and use it to do
things like size allocations add a comment noting the difference.

Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/include/uapi/asm/sve_context.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/include/uapi/asm/sve_context.h b/arch/arm64/include/uapi/asm/sve_context.h
index 754ab751b523..59f283f373a6 100644
--- a/arch/arm64/include/uapi/asm/sve_context.h
+++ b/arch/arm64/include/uapi/asm/sve_context.h
@@ -13,6 +13,10 @@
 
 #define __SVE_VQ_BYTES		16	/* number of bytes per quadword */
 
+/*
+ * Note that for future proofing __SVE_VQ_MAX is defined much larger
+ * than the actual architecture maximum of 16.
+ */
 #define __SVE_VQ_MIN		1
 #define __SVE_VQ_MAX		512
 

---
base-commit: 54be6c6c5ae8e0d93a6c4641cb7528eb0b6ba478
change-id: 20240206-arm64-sve-vl-max-comment-64efa3f03625

Best regards,
-- 
Mark Brown <broonie@...nel.org>