linux-kernel - [PATCH] math64: Provide an uprounding variant of mul_u64_u64_div

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Message-ID: <20250319171426.175460-2-u.kleine-koenig@baylibre.com>
Date: Wed, 19 Mar 2025 18:14:25 +0100
From: Uwe Kleine-König <u.kleine-koenig@...libre.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Nicolas Pitre <npitre@...libre.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] math64: Provide an uprounding variant of mul_u64_u64_div_u64()

This is needed (at least) in the pwm-stm32 driver. Currently the
pwm-stm32 driver implements this function itself. This private
implementation can be dropped as a followup of this patch.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...libre.com>
---
 include/linux/math64.h |  1 +
 lib/math/div64.c       | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/math64.h b/include/linux/math64.h
index 6aaccc1626ab..0c545b3ddaa5 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -283,6 +283,7 @@ static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 divisor)
 #endif /* mul_u64_u32_div */
 
 u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div);
+u64 mul_u64_u64_div_u64_roundup(u64 a, u64 mul, u64 div);
 
 /**
  * DIV64_U64_ROUND_UP - unsigned 64bit divide with 64bit divisor rounded up
diff --git a/lib/math/div64.c b/lib/math/div64.c
index 5faa29208bdb..66beb669992d 100644
--- a/lib/math/div64.c
+++ b/lib/math/div64.c
@@ -267,3 +267,18 @@ u64 mul_u64_u64_div_u64(u64 a, u64 b, u64 c)
 }
 EXPORT_SYMBOL(mul_u64_u64_div_u64);
 #endif
+
+#ifndef mul_u64_u64_div_u64_roundup
+u64 mul_u64_u64_div_u64_roundup(u64 a, u64 b, u64 c)
+{
+	u64 res = mul_u64_u64_div_u64(a, b, c);
+	/* Those multiplications might overflow but it doesn't matter */
+	u64 rem = a * b - c * res;
+
+	if (rem)
+		res += 1;
+
+	return res;
+}
+EXPORT_SYMBOL(mul_u64_u64_div_u64_roundup);
+#endif

base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
-- 
2.47.1