Re: [PATCH RFC] clk: ux500: add range to usleep_range

[Ulf Hansson]

On Sun, 7 Apr 2019 at 05:13, Nicholas Mc Guire <hofrat@xxxxxxxxxxx> 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@xxxxxxxxxxx>
> ---
>
> 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));

Kind regards
Uffe