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Date:   Thu, 11 Apr 2019 12:38:44 +0200
From:   Nicholas Mc Guire <der.herr@...r.at>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Nicholas Mc Guire <hofrat@...ntech.at>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [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@...ntech.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@...ntech.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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