[PATCH v4 3/5] clk: renesas: rcar-gen3: Support Z and Z2 clocks with high frequency parents

[Simon Horman]

Support Z and Z2 clocks with parent frequencies greater than UINT32_MAX Hz
(~4.29GHz).

The DIV_ROUND_CLOSEST_ULL() macro accepts a 64bit dividend and 32bit
divisor. This leads to truncation of the dividend, which is the Z or Z2
parent clock frequency in HZ, on platforms where frequency of that clock is
greater than UINT32_MAX Hz.

To resolve this problem the DIV64_U64_ROUND_CLOSEST() macro, which an
unsigned 32bit dividend and divisor, is introduced.

An earlier version of this patch made use of the existing
DIV_ROUND_CLOSEST() macro, which accepts the prevailing type of the
dividend and divisor. However, this does not compile on 32bit systems, such
as i386 and mips, when called with the types used at this callsite, an
unsigned long long dividend and unsigned long divisor.

This work is in preparation for supporting the Z2 cloco on the R-Car Gen3
E3 (r8a77990) SoC which has a 4.8GHz parent clock.

Signed-off-by: Simon Horman <horms+renesas@xxxxxxxxxxxx>
---
v4: Add and use DIV64_U64_ROUND_CLOSEST

v2: New patch
---
 drivers/clk/renesas/rcar-gen3-cpg.c |  4 ++--
 include/linux/math64.h              | 13 +++++++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/renesas/rcar-gen3-cpg.c b/drivers/clk/renesas/rcar-gen3-cpg.c
index 6b146c2cf6a3..4513bb705b03 100644
--- a/drivers/clk/renesas/rcar-gen3-cpg.c
+++ b/drivers/clk/renesas/rcar-gen3-cpg.c
@@ -120,8 +120,8 @@ static int cpg_z_clk_set_rate(struct clk_hw *hw, unsigned long rate,
 	unsigned int i;
 	u32 val, kick;
 
-	mult = DIV_ROUND_CLOSEST_ULL(rate * 32ULL * zclk->fixed_div,
-				     parent_rate);
+	mult = DIV64_U64_ROUND_CLOSEST(rate * 32ULL * zclk->fixed_div,
+				       parent_rate);
 	mult = clamp(mult, 1U, 32U);
 
 	if (readl(zclk->kick_reg) & CPG_FRQCRB_KICK)
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