Messages in this thread | | | Subject | Re: [PATCH v2] clk:mxs: Fix bug on frequency divider | From | Stefan Wahren <> | Date | Fri, 18 Sep 2015 09:21:17 +0200 |
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+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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