[Intel-gfx] [PATCH] drm: Disable all the possibles output/crtcs before entering KMS mode

[Eric Anholt]

On Fri, 4 Dec 2009 23:22:51 +0100, Rafał Miłecki <zajec5 at gmail.com> wrote:
> 2009/12/4 Dave Airlie <airlied at redhat.com>:
> > On Fri, 2009-12-04 at 20:05 +0800, yakui.zhao at intel.com wrote:
> >> From: Zhao Yakui <yakui.zhao at intel.com>
> >>
> >> Disable all the possible outputs/crtcs before entering KMS mode.
> >
> > We need a bit more info than this for such a large change?
> >
> > At one point we wanted to do smooth startup for LVDS panels,
> > so that we read back the mode and avoided reconfiguring them
> > this sort of change would totally go against it.
> >
> > Also I thought Arjan wanted to avoid slowdowns on startup,
> > which I would expect this to add to.
> 
> We have something like drm_disable_unused_functions. Isn't that
> supposed to make what you introduce there? At least at KMS booting
> when we don't have encoders/crtcs/outputs configured it should work
> for that. Am I wrong?

Yeah, drm_helper_disable_unused_functions with everything set to
disconnected should do this.  And if we want to get flicker-free
transitions, then we could read out current state for some outputs
and set our current state accordingly before calling that.  It's
something I've wanted to do since the original UMS work.

But it is true that if we aren't reading current state out, we do need
to turn everything off before modesetting.  The clocks can get very
angry at you otherwise, and you get things worse than a flicker at boot.

(So, my review of this patch is: close, but just use
drm_helper_disable_unused_functions instead of making a new function)
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