On Thu, 2015-03-19 at 23:34 -0700, Stephen Boyd wrote: > On 03/19, Andy Shevchenko wrote: > > We may do a calculation of the rounded rate based on (*prate / div) value in > > case it is not 0. It's as much higher as power of two of nearest value to > > (*prate / div / maxn). Thus, the patch replaces while-loop by direct > > calculations. > > > > While here, fix off-by-one error. maxn is the maximum value that can be > > hold by > > a register which means all ones in it. > > > > Signed-off-by: Andy Shevchenko <[email protected]> > > --- > > drivers/clk/clk-fractional-divider.c | 13 ++++++------- > > 1 file changed, 6 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/clk/clk-fractional-divider.c > > b/drivers/clk/clk-fractional-divider.c > > index 6aa72d9..4c0541b 100644 > > --- a/drivers/clk/clk-fractional-divider.c > > +++ b/drivers/clk/clk-fractional-divider.c > > @@ -14,6 +14,7 @@ > > #include <linux/device.h> > > #include <linux/slab.h> > > #include <linux/gcd.h> > > +#include <linux/log2.h> > > > > #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw) > > > > @@ -49,18 +50,16 @@ static long clk_fd_round_rate(struct clk_hw *hw, > > unsigned long rate, > > unsigned long *prate) > > { > > struct clk_fractional_divider *fd = to_clk_fd(hw); > > - unsigned maxn = (fd->nmask >> fd->nshift) + 1; > > - unsigned div; > > + unsigned maxn = fd->nmask >> fd->nshift; > > + unsigned long div, n; > > > > if (!rate || rate >= *prate) > > return *prate; > > > > div = gcd(*prate, rate); > > - > > - while ((*prate / div) > maxn) { > > - div <<= 1; > > - rate <<= 1; > > - } > > + n = *prate / div; > > + if (n > maxn) > > + return rate * roundup_pow_of_two(n / maxn); > > > > return rate; > > } > > Is there any reason why this code isn't using > rational_best_approximation() and mult_frac()?
For fist glance it should be faster that rational_best_approximation(), though less precise. I could switch to them. -- Andy Shevchenko <[email protected]> Intel Finland Oy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
