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

[Roman Beranek]

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>

Roman