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

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Message-ID: <20181029085843.3bslqwktxbp2ywk2@flea>
Date:   Mon, 29 Oct 2018 09:58:43 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Jagan Teki <jagan@...rulasolutions.com>
Cc:     Chen-Yu Tsai <wens@...e.org>, Icenowy Zheng <icenowy@...c.io>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Vasily Khoruzhick <anarsoul@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        David Airlie <airlied@...ux.ie>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        linux-clk <linux-clk@...r.kernel.org>,
        Michael Trimarchi <michael@...rulasolutions.com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH v2 02/15] clk: sunxi-ng: Add check for minimal rate to
 NKM PLLs

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@...tlin.com> 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@...rulasolutions.com>
> > > ---
> > > 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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