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[PATCH v2] clk:mxs: Fix bug on frequency divider

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On drivers/clk/mxs/clk-frac.c, the function clk_frac_round_rate returned a bad
result. The division before multiplication computes a wrong value ; the
calculation is inverted to fix the problem. The second issue is that the exact
rate have decimals and they are truncate. The consequence is that the function
clk_frac_set_rate (which use the result of clk_frac_round_rate) computes a
wrong value for the register (the rate generated can be closer to the desired
rate). The correction is : if there is decimal to the result, it is rounded to
the next larger integer.
On drivers/clk/mxs/clk-frac.c, the function clk_frac_recalc_rate returned
a bad result. The multiplication is made before the division to compute a
correct value.

Signed-off-by: Victorien Vedrine <victorien.vedrine@ophrys.net>
---
 drivers/clk/mxs/clk-frac.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/mxs/clk-frac.c b/drivers/clk/mxs/clk-frac.c
index e6aa6b5..b3fa7fa 100644
--- a/drivers/clk/mxs/clk-frac.c
+++ b/drivers/clk/mxs/clk-frac.c
@@ -42,11 +42,13 @@ static unsigned long clk_frac_recalc_rate(struct clk_hw *hw,
 {
 	struct clk_frac *frac = to_clk_frac(hw);
 	u32 div;
+	u64 tmp_rate;
 
 	div = readl_relaxed(frac->reg) >> frac->shift;
 	div &= (1 << frac->width) - 1;
 
-	return (parent_rate >> frac->width) * div;
+	tmp_rate = (u64)parent_rate * div;
+	return tmp_rate >> frac->width;
 }
 
 static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
@@ -55,7 +57,7 @@ static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
 	struct clk_frac *frac = to_clk_frac(hw);
 	unsigned long parent_rate = *prate;
 	u32 div;
-	u64 tmp;
+	u64 tmp, tmp_rate, result;
 
 	if (rate > parent_rate)
 		return -EINVAL;
@@ -68,7 +70,11 @@ static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
 	if (!div)
 		return -EINVAL;
 
-	return (parent_rate >> frac->width) * div;
+	tmp_rate = (u64)parent_rate * div;
+	result = tmp_rate >> frac->width;
+	if ((result << frac->width) < tmp_rate)
+		result += 1;
+	return result;
 }
 
 static int clk_frac_set_rate(struct clk_hw *hw, unsigned long rate,
-- 
1.9.1

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[PATCH v2] clk:mxs: Fix bug on frequency divider Victorien Vedrine <victorien.vedrine@ophrys.net> - 2015-08-31 10:50 +0200

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