linux-kernel - Re: [PATCH 3/3] drm: sun4i: calculate proper DCLK rate for DSI

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Message-ID: <87pm8lj709.fsf@oltmanns.dev>
Date:   Mon, 03 Apr 2023 17:08:33 +0200
From:   Frank Oltmanns <frank@...manns.dev>
To:     Roman Beranek <me@...y.cz>
Cc:     Maxime Ripard <mripard@...nel.org>, 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 3/3] drm: sun4i: calculate proper DCLK rate for DSI


On 2023-04-03 at 15:52:36 +0200, "Roman Beranek" <me@...y.cz> wrote:
> On Sun Apr 2, 2023 at 12:49 PM CEST, Frank Oltmanns wrote:
>>
>> When apply this to drm-next my panel stays dark. I haven't figured out
>> yet why, though. The other two patches in this series work fine, i.e.
>> they have no effect as they are just a refactoring.
>>
>> I'm testing this on my pinephone. It's the same with the patch I
>> submitted. For whatever reason, it no longer works on drm-next.
>
> I've reproduced the issue on my PinePhone and noticed that tcon0 had set
> pll-video0-2x as its parent instead of pll-mipi. Having tried a whole
> range of pll-video0 rates, I'm now convinced that DSI only works when
> tcon0 has pll-mipi as its parent.
>
> As little a change as setting .clock in the default mode of PP's panel
> to 73500 can fix it. Better yet, dropping pll-video0-2x from the set
> of acceptable parents for tcon0 fixes it universally. And that's what
> megi's kernel does, though the measure was introduced with a different
> rationale:
> <https://github.com/megous/linux/commit/7374d5756aa0cc3f11e494e3cbc54f6c7c01e1a8>

For sake of completeness, the patch you referenced builds on this patch:
https://github.com/megous/linux/commit/45e0aa8d9e34

Are you saying that your other boards and panels work without these
patches?

Best regards,
  Frank

>
> Roman