linux-kernel - Re: [PATCH v2 05/18] drm/sun4i: Force the mixer rate at 150MHz

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Date:   Tue, 28 Nov 2017 09:58:26 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Jernej Škrabec <jernej.skrabec@...l.net>
Cc:     Daniel Vetter <daniel.vetter@...el.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org,
        plaes@...es.org, icenowy@...c.io,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
Subject: Re: [PATCH v2 05/18] drm/sun4i: Force the mixer rate at 150MHz

On Mon, Nov 27, 2017 at 05:07:04PM +0100, Jernej Škrabec wrote:
> Hi Maxime,
> 
> Dne ponedeljek, 27. november 2017 ob 16:41:29 CET je Maxime Ripard napisal(a):
> > It seems like the mixer can only run properly when clocked at 150MHz. In
> > order to have something more robust than simply a fire-and-forget
> > assigned-clocks-rate, let's put that in the code.
> > 
> > Signed-off-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> > ---
> >  drivers/gpu/drm/sun4i/sun8i_mixer.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.c
> > b/drivers/gpu/drm/sun4i/sun8i_mixer.c index cb193c5f1686..c0cdccf772a2
> > 100644
> > --- a/drivers/gpu/drm/sun4i/sun8i_mixer.c
> > +++ b/drivers/gpu/drm/sun4i/sun8i_mixer.c
> > @@ -315,6 +315,13 @@ static int sun8i_mixer_bind(struct device *dev, struct
> > device *master, }
> >  	clk_prepare_enable(mixer->mod_clk);
> > 
> > +	/*
> > +	 * It seems that we need to enforce that rate for whatever
> > +	 * reason for the mixer to be functional. Make sure it's the
> > +	 * case.
> > +	 */
> > +	clk_set_rate(mixer->mod_clk, 150000000);
> > +
> 
> H3 mixer works at much higher rate and if we want to support tv out, it must 
> be dividable by 432 MHz, so either 432 MHz or maybe even 864 MHz.
> 
> We talked about that few months ago.
> 
> I guess this should be read from mixer configuration structure.

That works for me. Actually, I didn't need it at all for the LVDS
output on the A83t, the default seems to work just fine. Do you know
what it's related to? Maybe we can make that a bit more dynamic?

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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