* [PATCH v2] clk:mxs: Fix bug on frequency divider
[not found] ` <1441010707-17178-1-git-send-email-victorien.vedrine@ophrys.net>
@ 2015-09-18 7:21 ` Stefan Wahren
2015-09-24 12:17 ` Shawn Guo
0 siblings, 1 reply; 2+ messages in thread
From: Stefan Wahren @ 2015-09-18 7:21 UTC (permalink / raw)
To: linux-arm-kernel
+Shawn's new address
+linux-arm-kernel
> 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,
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