linux-kernel - Re: [PATCH review for 4.4 12/47] clk: wm831x: fix usleep

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Date:   Fri, 22 Sep 2017 09:46:28 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Nicholas Mc Guire <hofrat@...dl.org>,
        Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH review for 4.4 12/47] clk: wm831x: fix usleep_range with
 bad range

On Wed, Sep 20, 2017 at 04:45:02AM +0000, Levin, Alexander (Sasha Levin) wrote:
> From: Nicholas Mc Guire <hofrat@...dl.org>
> 
> [ Upstream commit ed784c532a3d0959db488f40a96c5127f63d42dc ]
> 
> The delay here is not in atomic context and does not seem critical with
> respect to precision, but usleep_range(min,max) with min==max results in
> giving the timer subsystem no room to optimize uncritical delays. Fix
> this by setting the range to 2000,3000 us.
> 
> Fixes: commit f05259a6ffa4 ("clk: wm831x: Add initial WM831x clock driver")
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> Acked-by: Charles Keepax <ckeepax@...nsource.wolfsonmicro.com>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> ---
>  drivers/clk/clk-wm831x.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/clk-wm831x.c b/drivers/clk/clk-wm831x.c
> index 763aed2de893..dfedcf5bc429 100644
> --- a/drivers/clk/clk-wm831x.c
> +++ b/drivers/clk/clk-wm831x.c
> @@ -101,7 +101,8 @@ static int wm831x_fll_prepare(struct clk_hw *hw)
>  	if (ret != 0)
>  		dev_crit(wm831x->dev, "Failed to enable FLL: %d\n", ret);
>  
> -	usleep_range(2000, 2000);
> +	/* wait 2-3 ms for new frequency taking effect */
> +	usleep_range(2000, 3000);

Does this patch really make sense for stable, isn't this really
just a small optimisation? The patch is pretty harmless so I
can't see applying it causing any problems, just curious what
problems not having it is causing.

Thanks,
Charles