linux-kernel - [PATCH] arm64/fpsimd: simplify sme

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Message-ID: <20250913000906.67086-1-yury.norov@gmail.com>
Date: Fri, 12 Sep 2025 20:09:05 -0400
From: "Yury Norov (NVIDIA)" <yury.norov@...il.com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Mark Brown <broonie@...nel.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Cc: "Yury Norov (NVIDIA)" <yury.norov@...il.com>
Subject: [PATCH] arm64/fpsimd: simplify sme_setup()

The function checks info->vq_map for emptiness right before calling
find_last_bit().

We can use the find_last_bit() output and save on bitmap_empty() call,
which is O(N).

Signed-off-by: Yury Norov (NVIDIA) <yury.norov@...il.com>
---
 arch/arm64/kernel/fpsimd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
index c37f02d7194e..e3f8f51748bc 100644
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1265,6 +1265,8 @@ void __init sme_setup(void)
 	if (!system_supports_sme())
 		return;
 
+	min_bit = find_last_bit(info->vq_map, SVE_VQ_MAX);
+
 	/*
 	 * SME doesn't require any particular vector length be
 	 * supported but it does require at least one.  We should have
@@ -1272,9 +1274,8 @@ void __init sme_setup(void)
 	 * let's double check here.  The bitmap is SVE_VQ_MAP sized for
 	 * sharing with SVE.
 	 */
-	WARN_ON(bitmap_empty(info->vq_map, SVE_VQ_MAX));
+	WARN_ON(min_bit >= SVE_VQ_MAX);
 
-	min_bit = find_last_bit(info->vq_map, SVE_VQ_MAX);
 	info->min_vl = sve_vl_from_vq(__bit_to_vq(min_bit));
 
 	max_bit = find_first_bit(info->vq_map, SVE_VQ_MAX);
-- 
2.43.0