linux-kernel - Re: [PATCH] clk: at91: avoid sleeping early

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Date:   Tue, 24 Sep 2019 13:20:15 -0700
From:   Stephen Boyd <sboyd@...nel.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        <u.kleine-koenig@...gutronix.de>
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Michael Turquette <mturquette@...libre.com>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] clk: at91: avoid sleeping early

Quoting Uwe  (2019-09-24 05:21:47)
> On Fri, Sep 20, 2019 at 05:39:06PM +0200, Alexandre Belloni wrote:
> > Note that this was already discussed a while ago and Arnd said this approach was
> > reasonable:
> >   https://lore.kernel.org/lkml/6120818.MyeJZ74hYa@wuerfel/
> > 
> >  drivers/clk/at91/clk-main.c |  5 ++++-
> >  drivers/clk/at91/sckc.c     | 20 ++++++++++++++++----
> >  2 files changed, 20 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/clk/at91/clk-main.c b/drivers/clk/at91/clk-main.c
> > index f607ee702c83..ccd48e7a3d74 100644
> > --- a/drivers/clk/at91/clk-main.c
> > +++ b/drivers/clk/at91/clk-main.c
> > @@ -293,7 +293,10 @@ static int clk_main_probe_frequency(struct regmap *regmap)
> >               regmap_read(regmap, AT91_CKGR_MCFR, &mcfr);
> >               if (mcfr & AT91_PMC_MAINRDY)
> >                       return 0;
> > -             usleep_range(MAINF_LOOP_MIN_WAIT, MAINF_LOOP_MAX_WAIT);
> > +             if (system_state < SYSTEM_RUNNING)
> > +                     udelay(MAINF_LOOP_MIN_WAIT);
> > +             else
> > +                     usleep_range(MAINF_LOOP_MIN_WAIT, MAINF_LOOP_MAX_WAIT);
> 
> Given that this construct is introduced several times, I wonder if we
> want something like:
> 
>         static inline void early_usleep_range(unsigned long min, unsigned long max)
>         {
>                 if (system_state < SYSTEM_RUNNING)
>                         udelay(min);
>                 else
>                         usleep_range(min, max);
>         }
> 

Maybe, but I think the intent is to not encourage this behavior? So
providing a wrapper will make it "easy" and then we'll have to tell
users to stop calling it. Another idea would be to make usleep_range()
"do the right thing" and call udelay if the system isn't running. And
another idea from tlgx[1] is to pull the delay logic into another clk op
that we can call to see when the enable or prepare is done. That may be
possible by introducing another clk_ops callback that when present
indicates we should sleep or delay for so much time while waiting for
the prepare or enable to complete.

[1] https://lkml.kernel.org/r/alpine.DEB.2.11.1606061448010.28031@nanos