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clk:mxs: Fix bug on frequency divider 

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>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
This commit is contained in:
Victorien Vedrine 2015-08-31 10:45:07 +02:00 committed by Stephen Boyd
parent a1c22a4be7
commit d87574332c
1 changed files with 9 additions and 3 deletions
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12
drivers/clk/mxs/clk-frac.c
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@ -41,11 +41,13 @@ static unsigned long clk_frac_recalc_rate(struct clk_hw *hw,
{ {
struct clk_frac *frac = to_clk_frac(hw); struct clk_frac *frac = to_clk_frac(hw);
u32 div; u32 div;
u64 tmp_rate;
div = readl_relaxed(frac->reg) >> frac->shift; div = readl_relaxed(frac->reg) >> frac->shift;
div &= (1 << frac->width) - 1; 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, static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
@ -54,7 +56,7 @@ static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
struct clk_frac *frac = to_clk_frac(hw); struct clk_frac *frac = to_clk_frac(hw);
unsigned long parent_rate = *prate; unsigned long parent_rate = *prate;
u32 div; u32 div;
u64 tmp; u64 tmp, tmp_rate, result;
if (rate > parent_rate) if (rate > parent_rate)
return -EINVAL; return -EINVAL;
@ -67,7 +69,11 @@ static long clk_frac_round_rate(struct clk_hw *hw, unsigned long rate,
if (!div) if (!div)
return -EINVAL; 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, static int clk_frac_set_rate(struct clk_hw *hw, unsigned long rate,