linux-kernel - [PATCH] ARM: vfp: Improve data types for divisors mh and ml

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Date: Fri, 28 Jun 2024 07:44:06 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: linux@...linux.org.uk
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Thorsten Blum <thorsten.blum@...lux.com>
Subject: [PATCH] ARM: vfp: Improve data types for divisors mh and ml

The divisors mh and ml can both be u32 instead of u64.

Since do_div() implicitly casts the divisors from u64 to u32, changing
their data types to u32 also removes the following Coccinelle warnings
reported by do_div.cocci:

  arch/arm/vfp/vfp.h:121:2-8: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.
  arch/arm/vfp/vfp.h:135:2-8: WARNING: do_div() does a 64-by-32 division, please consider using div64_u64 instead.

Use upper_32_bits() to compare 32-bit numbers instead of 64-bit numbers
and to prevent the warning:

  left shift count >= width of type [-Wshift-count-overflow]

Compile-tested only.

Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
---
 arch/arm/vfp/vfp.h | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/arm/vfp/vfp.h b/arch/arm/vfp/vfp.h
index e43a630f8a16..29073d89ef00 100644
--- a/arch/arm/vfp/vfp.h
+++ b/arch/arm/vfp/vfp.h
@@ -109,12 +109,13 @@ static inline u64 vfp_hi64multiply64(u64 n, u64 m)
 
 static inline u64 vfp_estimate_div128to64(u64 nh, u64 nl, u64 m)
 {
-	u64 mh, ml, remh, reml, termh, terml, z;
+	u64 remh, reml, termh, terml, z;
+	u32 mh, ml;
 
 	if (nh >= m)
 		return ~0ULL;
 	mh = m >> 32;
-	if (mh << 32 <= nh) {
+	if (mh <= upper_32_bits(nh)) {
 		z = 0xffffffff00000000ULL;
 	} else {
 		z = nh;
@@ -129,7 +130,7 @@ static inline u64 vfp_estimate_div128to64(u64 nh, u64 nl, u64 m)
 		add128(&remh, &reml, remh, reml, mh, ml);
 	}
 	remh = (remh << 32) | (reml >> 32);
-	if (mh << 32 <= remh) {
+	if (mh <= upper_32_bits(remh)) {
 		z |= 0xffffffff;
 	} else {
 		do_div(remh, mh);
-- 
2.45.2