Re: How should "max bpc" KMS property work?

[Pekka Paalanen <ppaalanen@gmail.com>]

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On Wed, 25 May 2022 06:04:44 +0000
Simon Ser <contact@emersion.fr> wrote:

> On Wednesday, May 25th, 2022 at 00:03, Alex Deucher <alexdeucher@gmail.com> wrote:
> 
> > > Why would anyone want to run at 8bpc when they have a panel with
> > > higher color depth? So I think someone is going to be doing that
> > > modeset eventually anyway.  
> >
> > We used to do something similar, but then got piles of bug reports
> > about the displays running at 30Hz rather than 60 so we changed it to
> > 8. It's hard to say what a user will prefer.  
> 
> "max bpc" is a maximum, ie. it shouldn't make a modeset fail, the kernel
> should automatically reduce the bpc if the link bandwidth is insufficient.
> So that sounds like there's an amdgpu bug here?

Yes, that's an amdgpu bug in my opinion too. A video mode is always
explicit about timings, while "max bpc" is just a max and not "use this
exactly", so I believe the explicit setting should win.

There is no "use this bpc exactly" KMS UAPI yet.


Thanks,
pq

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