linux-kernel - Re: [PATCH V2] clk: ux500: add range to usleep

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Date:   Thu, 11 Apr 2019 13:07:08 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Nicholas Mc Guire <hofrat@...ntech.at>
Cc:     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 V2] clk: ux500: add range to usleep_range

On Thu, 11 Apr 2019 at 13:04, 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. With the expected range for
> enable_delay_us being milliseconds, the range should lie in the 250us
> range which is sufficient for hrtimer optimization.
>
> Signed-off-by: Nicholas Mc Guire <hofrat@...ntech.at>

Acked-by: Ulf Hansson <ulf.hansson@...aro.org>

Kind regards
Uffe

> ---
>
> Problem located with an experimental coccinelle script
> V2: As clarified by Ulf Hansson <ulf.hansson@...aro.org> the delays
>     here are typically in the millisecond range - so as proposed
>     replace the factor 2 by a 25% increase of max.
>
> Patch was compile tested with: u8500_defconfig (implies COMMON_CLK=y)
> (with some unrelated sparse warnings about not implemented system calls)
> Patch is against 5.1-rc4 (localversion-next is next=20190410)
>
>  drivers/clk/ux500/clk-sysctrl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clk/ux500/clk-sysctrl.c b/drivers/clk/ux500/clk-sysctrl.c
> index 7c0403b..698306f 100644
> --- a/drivers/clk/ux500/clk-sysctrl.c
> +++ b/drivers/clk/ux500/clk-sysctrl.c
> @@ -42,7 +42,8 @@ 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 +
> +                            (clk->enable_delay_us >> 2));
>
>         return ret;
>  }
> --
> 2.1.4
>