[Intel-gfx] [PATCH] xf86-video-intel: deactivate unused CRTCs

Helge Bahmann helge.bahmann at secunet.com
Mon Mar 26 15:30:49 CEST 2012

On Monday 26 March 2012 14:22:02 Chris Wilson wrote:
> On Thu, 15 Dec 2011 13:46:28 +0100, Helge Bahmann <helge.bahmann at secunet.com> wrote:
> > Hi everyone,
> >
> > would you mind putting something along the following into
> > xf86-video-intel?
> A few months later... I looked at this and concluded that it is just
> working around a kernel bug, which I'm always optimistic will be
> resolved in the next release.
> -Chris

Most likely there is a "bug" in my understandig of how X-Server and drm console layer are supposed 
to cooperate:

- how does the kernel layer reliably distinguish between the states "userspace manages display heads 
vs. "kernel console layer manages display heads" ?
- how does the kernel layer reliably detect the "ground state" from which userspace starts setting 
up things ?
- what assumptions may user-space make on the "left-over" state when it takes over responsibility?

I don't think kernel code currently handles these issues too well, resulting in a number of odd 
corner cases when plugging/unplugging displays at the "right" times (while switched away from X, 
while in suspend-to-ram state, while X server resumes but is slow to re-setup things because it got 
paged out...). My best shot at fixing this was to have X not make too many assumptions on the state 
after taking over, and bring everything into a well-defined state.

Could you perhaps briefly explain how the interaction is supposed to look? I would really like to 
provide a more "correct" fix, but I don't fully grasp the intended model so far.

Best regards
Helge Bahmann
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