Re: [PATCH v2 02/15] clk: sunxi-ng: Add check for minimal rate to NKM PLLs

[Maxime Ripard]

On Thu, Oct 25, 2018 at 04:25:59PM +0530, Jagan Teki wrote:
> On Wed, Oct 24, 2018 at 11:34 PM Maxime Ripard
> <maxime.ripard@xxxxxxxxxxx> wrote:
> >
> > On Tue, Oct 23, 2018 at 09:20:22PM +0530, Jagan Teki wrote:
> > > Some NKM PLLs doesn't work well when their output clock rate is set below
> > > certain rate.
> > >
> > > So, add support for minimal rate for relevant PLLs.
> > >
> > > Signed-off-by: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> > > ---
> > > Changes for v2:
> > > - new patch
> > >
> > >  drivers/clk/sunxi-ng/ccu_nkm.c | 7 +++++++
> > >  drivers/clk/sunxi-ng/ccu_nkm.h | 1 +
> > >  2 files changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
> > > index 841840e35e61..d17539dc88dd 100644
> > > --- a/drivers/clk/sunxi-ng/ccu_nkm.c
> > > +++ b/drivers/clk/sunxi-ng/ccu_nkm.c
> > > @@ -125,6 +125,13 @@ static unsigned long ccu_nkm_round_rate(struct ccu_mux_internal *mux,
> > >       if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
> > >               rate *= nkm->fixed_post_div;
> > >
> > > +     if (rate < nkm->min_rate) {
> > > +             rate = nkm->min_rate;
> > > +             if (nkm->common.features & CCU_FEATURE_FIXED_POSTDIV)
> > > +                     rate /= nkm->fixed_post_div;
> >
> > I'm not sure this is right. Is the post divider taken into account to
> > calculate the minimum, or is the minimum on the rate before the fixed
> > post divider.
> 
> Since we are returning from here, we need to take care post div which
> is actually doing at the end of round_rate.

That's not my point though. Does the rate needs to be superior to min
/ post_div, or min?

> >
> > How did you test this?
> 
> I've not used this on PLL_MIPI atleast, so I didn't test this.

If you've never tested this, why are you adding that code?

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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