linux-kernel - [PATCH v4 33/40] sh: mach-x3proto: optimize ilsel

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Date: Thu, 20 Jun 2024 10:56:56 -0700
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org,
	Yoshinori Sato <ysato@...rs.sourceforge.jp>,
	Rich Felker <dalias@...c.org>,
	John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Yury Norov <yury.norov@...il.com>,
	linux-sh@...r.kernel.org
Cc: Alexey Klimov <alexey.klimov@...aro.org>,
	Bart Van Assche <bvanassche@....org>,
	Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Mirsad Todorovac <mirsad.todorovac@....unizg.hr>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Shtylyov <s.shtylyov@....ru>
Subject: [PATCH v4 33/40] sh: mach-x3proto: optimize ilsel_enable()

Simplify ilsel_enable() by using find_and_set_bit().

Geert also pointed the bug in the old implementation:

	I don't think the old code worked as intended: the first time
	no free bit is found, bit would have been ILSEL_LEVELS, and
	test_and_set_bit() would have returned false, thus terminating
	the loop, and continuing with an out-of-range bit value? Hence
	to work correctly, bit ILSEL_LEVELS of ilsel_level_map should
	have been initialized to one?  Or am I missing something?

The new code does not have that issue.

CC: John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>
Signed-off-by: Yury Norov <yury.norov@...il.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 arch/sh/boards/mach-x3proto/ilsel.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/sh/boards/mach-x3proto/ilsel.c b/arch/sh/boards/mach-x3proto/ilsel.c
index f0d5eb41521a..35b585e154f0 100644
--- a/arch/sh/boards/mach-x3proto/ilsel.c
+++ b/arch/sh/boards/mach-x3proto/ilsel.c
@@ -8,6 +8,7 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/find_atomic.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -99,8 +100,8 @@ int ilsel_enable(ilsel_source_t set)
 	}
 
 	do {
-		bit = find_first_zero_bit(&ilsel_level_map, ILSEL_LEVELS);
-	} while (test_and_set_bit(bit, &ilsel_level_map));
+		bit = find_and_set_bit(&ilsel_level_map, ILSEL_LEVELS);
+	} while (bit >= ILSEL_LEVELS);
 
 	__ilsel_enable(set, bit);
 
-- 
2.43.0