linux-kernel - [PATCH 5/9] bitfield: FIELD_MODIFY: Only do a single read/write on the target

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Message-Id: <20251209100313.2867-6-david.laight.linux@gmail.com>
Date: Tue,  9 Dec 2025 10:03:09 +0000
From: david.laight.linux@...il.com
To: Yury Norov <yury.norov@...il.com>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	Crt Mori <cmo@...exis.com>,
	Richard Genoud <richard.genoud@...tlin.com>,
	Andy Shevchenko <andriy.shevchenko@...el.com>,
	Luo Jie <quic_luoj@...cinc.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Jakub Kicinski <kuba@...nel.org>,
	netdev@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>,
	Simon Horman <simon.horman@...ronome.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Andreas Noever <andreas.noever@...il.com>,
	Yehezkel Bernat <YehezkelShB@...il.com>,
	Nicolas Frattaroli <nicolas.frattaroli@...labora.com>
Cc: David Laight <david.laight.linux@...il.com>
Subject: [PATCH 5/9] bitfield: FIELD_MODIFY: Only do a single read/write on the target

From: David Laight <david.laight.linux@...il.com>

Replace the:
        *reg &= ~mask; *reg |= new_value;
with a single assignment.
While the compiler will usually optimise the extra access away
it isn't guaranteed.

Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 include/linux/bitfield.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 3e013da9ea12..3e0e8533bb66 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -200,8 +200,7 @@
 		__auto_type _val = 1 ? (val) : _mask;					\
 		typecheck_pointer(_reg_p);						\
 		__BF_FIELD_CHECK(_mask, *_reg_p, _val, "FIELD_MODIFY: ");		\
-		*_reg_p &= ~_mask;							\
-		*_reg_p |= ((_val << __bf_shf(_mask)) & _mask);				\
+		*_reg_p = (*_reg_p & ~_mask) | ((_val << __bf_shf(_mask)) & _mask);	\
 	})
 
 extern void __compiletime_error("value doesn't fit into mask")
-- 
2.39.5