[Intel-gfx] hotplug CRT detection

[Dave Airlie]

So I've been reviewing the i915/ironlake CRT detect code and am a bit confused.

I though on the i945 and above that we had proper CRT hotplug
detection with an IRQ, that didn't require any polling.

Now looking at the code when we do a CRT detect, the first thing we do
is try the hotplug method, however on ILK/SNB this is crap and
requires powering off the ADPA, which turns off the monitor, if that
fails we fallback to DDC probing which is pretty non-destructive.

I get the feeling the whole hotplug detect code is pointless if the
hardware is already meant to send us an IRQ when something happens, or
at least I think the DDC probe should be > than the hotplug probe if
the hotplug probe is too remain destructive.

Dave.