linux-kernel - Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from TCON0_DCLK

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Message-ID: <qrjzn5dy7qasjubovofyzsazakiqpsjyyt2av6kfbqq7mqcdqe@bvs2egtopbqs>
Date:   Wed, 12 Apr 2023 16:09:54 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Roman Beranek <romanberanek@...oud.com>
Cc:     Frank Oltmanns <frank@...manns.dev>, Chen-Yu Tsai <wens@...e.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/sun4i: uncouple DSI dotclock divider from
 TCON0_DCLK_REG

On Wed, Apr 12, 2023 at 09:14:59AM +0200, Roman Beranek wrote:
> On Wed Apr 5, 2023 at 5:03 PM CEST, Maxime Ripard wrote:
> > On Wed, Apr 05, 2023 at 02:34:11PM +0200, Roman Beranek wrote:
> > > It turns out however that the new dclk rates can't be set exactly as
> > > requested without touching pll-video0*, tcon0 now therefore gets
> > > reparented from pll-mipi to pll-video0-2x which, as it further turns
> > > out, breaks DSI. While simply forbidding the video0-2x mux option seems
> > > to me as the right way to go because there's not much use for it with
> > > non-DSI interfaces either besides the opportunity to power pll-mipi
> > > down, I'd like to run by you first.
> >
> > Sounds reasonable
> 
> Okay, I'm unsure of how to denote that in the code however. Should I
> just comment the parent out of the table and put an explanation in
> a comment nearby? Or just erase it? I couldn't find an applicable
> precedent.

I think that forcing the parent at boot, and adding the
CLK_SET_RATE_NOREPARENT flag should be enough.

> > > * As pll-mipi doesn't have CLK_SET_RATE_PARENT flag set, pll-video0
> > >   retains its boot-time rate of 294 MHz set by sunxi-dw-hdmi driver
> > >   in u-boot. Why 294 MHz (as opposed to the default rate of 297 MHz)?
> > >   The driver actually asks for 297 MHz, clock_set_pll3 rounds it to
> > >   294 MHz though because it limits itself to 6 MHz steps.
> >
> > We could also address that though
> 
> Should I include it in v2 of the series, or leave it for later?

I guess you can include it into this one too

Maxime

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