linux-kernel - [PATCH v5 3/6] math64: New DIV64_U64_ROUND

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Date:   Mon, 11 Feb 2019 14:58:55 +0100
From:   Simon Horman <horms+renesas@...ge.net.au>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Magnus Damm <magnus.damm@...il.com>,
        linux-renesas-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        Fabrizio Castro <fabrizio.castro@...renesas.com>,
        Biju Das <biju.das@...renesas.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Simon Horman <horms+renesas@...ge.net.au>
Subject: [PATCH v5 3/6] math64: New DIV64_U64_ROUND_CLOSEST helper

Provide DIV64_U64_ROUND_CLOSEST helper which performs division rounded to
the closes integer using an unsigned 64bit dividend and divisor.

This will be used in a follow-up patch to allow calculation of clock
divisors with high frequency parents in the R-Car Gen3 CPG MSSR driver
where ovefolow occurs if either the dividend or divisor is 32bit.

Signed-off-by: Simon Horman <horms+renesas@...ge.net.au>
---
v5: New separate patch to add DIV64_U64_ROUND_CLOSEST
---
 include/linux/math64.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/math64.h b/include/linux/math64.h
index bb2c84afb80c..65bef21cdddb 100644
--- a/include/linux/math64.h
+++ b/include/linux/math64.h
@@ -284,4 +284,17 @@ static inline u64 mul_u64_u32_div(u64 a, u32 mul, u32 divisor)
 #define DIV64_U64_ROUND_UP(ll, d)	\
 	({ u64 _tmp = (d); div64_u64((ll) + _tmp - 1, _tmp); })
 
+/**
+ * DIV64_U64_ROUND_CLOSEST - unsigned 64bit divide with 64bit divisor rounded to nearest integer
+ * @dividend: unsigned 64bit dividend
+ * @divisor: unsigned 64bit divisor
+ *
+ * Divide unsigned 64bit dividend by unsigned 64bit divisor
+ * and round to closest integer.
+ *
+ * Return: dividend / divisor rounded to nearest integer
+ */
+#define DIV64_U64_ROUND_CLOSEST(dividend, divisor)	\
+	({ u64 _tmp = (divisor); div64_u64((dividend) + _tmp / 2, _tmp); })
+
 #endif /* _LINUX_MATH64_H */
-- 
2.11.0