Re: [PATCH] clk: at91: avoid sleeping early

From: Stephen Boyd
Date: Tue Sep 24 2019 - 16:20:18 EST


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