Quoting Tomi Valkeinen (2014-03-17 05:53:03) > On 27/02/14 04:25, Mike Turquette wrote: > > Quoting Tero Kristo (2014-02-14 05:45:22) > >> On 02/13/2014 12:03 PM, Tomi Valkeinen wrote: > >>> clk-divider.c does not calculate the rates consistently at the moment. > >>> > >>> As an example, on OMAP3 we have a clock divider with a source clock of > >>> 864000000 Hz. With dividers 6, 7 and 8 the theoretical rates are: > >>> > >>> 6: 144000000 > >>> 7: 123428571.428571... > >>> 8: 108000000 > >>> > >>> Calling clk_round_rate() with the rate in the first column will give the > >>> rate in the second column: > >>> > >>> 144000000 -> 144000000 > >>> 143999999 -> 123428571 > >>> 123428572 -> 123428571 > >>> 123428571 -> 108000000 > >>> > >>> Note how clk_round_rate() returns 123428571 for rates from 123428572 to > >>> 143999999, which is mathematically correct, but when clk_round_rate() is > >>> called with 123428571, the returned value is surprisingly 108000000. > >>> > >>> This means that the following code works a bit oddly: > >>> > >>> rate = clk_round_rate(clk, 123428572); > >>> clk_set_rate(clk, rate); > >>> > >>> As clk_set_rate() also does clock rate rounding, the result is that the > >>> clock is set to the rate of 108000000, not 123428571 returned by the > >>> clk_round_rate. > >>> > >>> This patch changes the clk-divider.c to use DIV_ROUND_UP when > >>> calculating the rate. This gives the following behavior which fixes the > >>> inconsistency: > >>> > >>> 144000000 -> 144000000 > >>> 143999999 -> 123428572 > >>> 123428572 -> 123428572 > >>> 123428571 -> 108000000 > >>> > >>> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxx> > >>> Cc: Mike Turquette <mturquette@xxxxxxxxxx> > >>> --- > >>> drivers/clk/clk-divider.c | 10 +++++----- > >>> 1 file changed, 5 insertions(+), 5 deletions(-) > >>> > >>> diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c > >>> index 5543b7df8e16..ec22112e569f 100644 > >>> --- a/drivers/clk/clk-divider.c > >>> +++ b/drivers/clk/clk-divider.c > >>> @@ -24,7 +24,7 @@ > >>> * Traits of this clock: > >>> * prepare - clk_prepare only ensures that parents are prepared > >>> * enable - clk_enable only ensures that parents are enabled > >>> - * rate - rate is adjustable. clk->rate = parent->rate / divisor > >>> + * rate - rate is adjustable. clk->rate = DIV_ROUND_UP(parent->rate / divisor) > >>> * parent - fixed parent. No clk_set_parent support > >>> */ > >>> > >>> @@ -115,7 +115,7 @@ static unsigned long clk_divider_recalc_rate(struct clk_hw *hw, > >>> return parent_rate; > >>> } > >>> > >>> - return parent_rate / div; > >>> + return DIV_ROUND_UP(parent_rate, div); > >>> } > >>> > >>> /* > >>> @@ -185,7 +185,7 @@ static int clk_divider_bestdiv(struct clk_hw *hw, unsigned long rate, > >>> } > >>> parent_rate = __clk_round_rate(__clk_get_parent(hw->clk), > >>> MULT_ROUND_UP(rate, i)); > >>> - now = parent_rate / i; > >>> + now = DIV_ROUND_UP(parent_rate, i); > >>> if (now <= rate && now > best) { > >>> bestdiv = i; > >>> best = now; > >>> @@ -207,7 +207,7 @@ static long clk_divider_round_rate(struct clk_hw *hw, unsigned long rate, > >>> int div; > >>> div = clk_divider_bestdiv(hw, rate, prate); > >>> > >>> - return *prate / div; > >>> + return DIV_ROUND_UP(*prate, div); > >>> } > >>> > >>> static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate, > >>> @@ -218,7 +218,7 @@ static int clk_divider_set_rate(struct clk_hw *hw, unsigned long rate, > >>> unsigned long flags = 0; > >>> u32 val; > >>> > >>> - div = parent_rate / rate; > >>> + div = DIV_ROUND_UP(parent_rate, rate); > >>> value = _get_val(divider, div); > >>> > >>> if (value > div_mask(divider)) > >>> > >> > >> Basically the patch looks good to me, but it might be good to have a > >> testing round of sort with this. It can potentially cause regressions on > >> multiple boards if the drivers happen to rely on the "broken" clock > >> rates. Same for patch #2 which is a copy paste of this one, but only > >> impacts TI boards. > > > > Agreed. I've taken patches #1 & #2 into clk-next. Let's let them stew in > > -next for a while and see if anyone's board catches on fire. > > Are these on the way to 3.15? Yes, they've been in -next for a couple of weeks. Regards, Mike > > Tomi > > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html