Re: [PATCH] clk: Re-evaluate clock rate on min/max update

From: Peter De Schrijver
Date: Thu Apr 13 2017 - 03:49:33 EST


On Wed, Apr 12, 2017 at 09:46:05AM -0700, Stephen Boyd wrote:
> On 03/21, Peter De Schrijver wrote:
> > Whenever a user change its min or max rate limit of a clock, we need to
> > re-evaluate the current clock rate and possibly change it if the new limits
> > require so. To do this clk_set_rate_range() already calls
> > clk_core_set_rate_nolock, however this won't have the intended effect
> > because the core clock rate hasn't changed. To fix this, move the test to
> > avoid setting the same core clock rate again, to clk_set_rate() so
> > clk_core_set_rate_nolock() can change the clock rate when min or max have
> > been updated, even when the core clock rate has not changed.
>
> I'd expect some sort of Fixes: tag here? Or it never worked!?

I don't think this ever worked.

>
> >
> > Signed-off-by: Peter De Schrijver <pdeschrijver@xxxxxxxxxx>
>
> I seem to recall some problems here around rate aggregation that
> we fixed after the patches merged. Sorry, but I have to go back
> and look at those conversations to refresh my memory and make
> sure this is all fine.
>
> Are you relying on the rate setting op to be called with the new
> min/max requirements if the aggregated rate is the same? I don't
> understand why clk drivers care.
>

No. But I do rely on the rate setting op to be called when a new min or max
rate would cause the rate to be changed even when there is no new rate request.

Eg:

min = 100MHz, max = 500MHz, current rate request is 400MHz, then max changes to
300MHz. Today the rate setting op will not be called, while I think it should
be called to lower the rate to 300MHz.

Peter.



> > ---
> > drivers/clk/clk.c | 13 +++++++------
> > 1 file changed, 7 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index 2fa2fb8..0b815d1 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -1569,10 +1569,6 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
> > if (!core)
> > return 0;
> >
> > - /* bail early if nothing to do */
> > - if (rate == clk_core_get_rate_nolock(core))
> > - return 0;
> > -
> > if ((core->flags & CLK_SET_RATE_GATE) && core->prepare_count)
> > return -EBUSY;
> >
> > @@ -1621,16 +1617,21 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
> > */
> > int clk_set_rate(struct clk *clk, unsigned long rate)
> > {
> > - int ret;
> > + int ret = 0;
> >
> > if (!clk)
> > - return 0;
> > + return ret;
>
> Why? Noise?
>
> >
> > /* prevent racing with updates to the clock topology */
> > clk_prepare_lock();
> >
> > + /* bail early if nothing to do */
> > + if (rate == clk_core_get_rate_nolock(clk->core))
> > + goto out;
> > +
> > ret = clk_core_set_rate_nolock(clk->core, rate);
> >
> > +out:
> > clk_prepare_unlock();
> >
>
> --
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