linux-kernel - [PATCH 2/5] ARM: findbit: provide more efficient ARMv7 implementation

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Message-Id: <E1ooSWU-000FE4-9D@rmk-PC.armlinux.org.uk>
Date:   Fri, 28 Oct 2022 17:47:58 +0100
From:   "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>
To:     Yury Norov <yury.norov@...il.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Mark Rutland <mark.rutland@....com>,
        Will Deacon <will@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 2/5] ARM: findbit: provide more efficient ARMv7 implementation

Provide a more efficient ARMv7 implementation to determine the first
set bit in the supplied value.

Signed-off-by: Russell King (Oracle) <rmk@...linux.org.uk>
---
 arch/arm/lib/findbit.S | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/arm/lib/findbit.S b/arch/arm/lib/findbit.S
index 4c584bc4704b..256e095d490b 100644
--- a/arch/arm/lib/findbit.S
+++ b/arch/arm/lib/findbit.S
@@ -170,7 +170,11 @@ ENDPROC(_find_next_bit_be)
  * One or more bits in the LSB of r3 are assumed to be set.
  */
 .L_found:
-#if __LINUX_ARM_ARCH__ >= 5
+#if __LINUX_ARM_ARCH__ >= 7
+		rbit	r3, r3			@ reverse bits
+		clz	r3, r3			@ count high zero bits
+		add	r0, r2, r3		@ add offset of first set bit
+#elif __LINUX_ARM_ARCH__ >= 5
 		rsb	r0, r3, #0
 		and	r3, r3, r0		@ mask out lowest bit set
 		clz	r3, r3			@ count high zero bits
-- 
2.30.2