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

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Message-Id: <CRULBWW4VCWG.3KS7HX7P1G4P6@void.crly.cz>
Date:   Wed, 12 Apr 2023 09:14:59 +0200
From:   "Roman Beranek" <romanberanek@...oud.com>
To:     "Maxime Ripard" <maxime@...no.tech>
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 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.

> > * 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?

Thanks,
Roman