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SubjectRe: [PATCH RFC] clk: ux500: add range to usleep_range
On Thu, Apr 11, 2019 at 11:36:45AM +0200, Ulf Hansson wrote:
> On Sun, 7 Apr 2019 at 05:13, Nicholas Mc Guire <hofrat@opentech.at> wrote:
> >
> > Providing a range for usleep_range() allows the hrtimer subsystem to
> > coalesce timers - the delay is runtime configurable so a factor 2
> > is taken to provide the range.
> >
> > Signed-off-by: Nicholas Mc Guire <hofrat@opentech.at>
> > ---
> >
> > Problem located with an experimental coccinelle script
> >
> > Q: Basically usleep_range() with min == max never makes much sense notably
> > in non-atomic context. If the factor of 2 is tolerable or a fixed
> > offset of e.g. 1000 would be more suitable is not clear to me - maybe
> > someone familiar with that driver can clarify this.
> >
> > Patch was compile tested with: u8500_defconfig (implies COMMON_CLK=y)
> > (with some sparse warnings about not implemented system calls)
> >
> > Patch is against 5.1-rc3 (localversion-next is next=20190405)
> >
> > drivers/clk/ux500/clk-sysctrl.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/clk/ux500/clk-sysctrl.c b/drivers/clk/ux500/clk-sysctrl.c
> > index 7c0403b..a1fa3fb 100644
> > --- a/drivers/clk/ux500/clk-sysctrl.c
> > +++ b/drivers/clk/ux500/clk-sysctrl.c
> > @@ -42,7 +42,7 @@ static int clk_sysctrl_prepare(struct clk_hw *hw)
> > clk->reg_bits[0]);
> >
> > if (!ret && clk->enable_delay_us)
> > - usleep_range(clk->enable_delay_us, clk->enable_delay_us);
> > + usleep_range(clk->enable_delay_us, clk->enable_delay_us*2);
>
> The range being used is actually in ms, so not sure we actually need
> to double it for the range.
>
> How about adding ~25% instead, along the lines of below:
> usleep_range(clk->enable_delay_us, clk->enable_delay_us +
> (clk->enable_delay_us >> 2));
>
that would be perfectly sufficient for hrtimers - if the range is
in ms - so I´ll send out a V2 shortly.

thx!
hofrat

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