[Intel-gfx] [PATCH 4/6] drm/i915: enable VT switchless resume v2

[Daniel Vetter]

On Tue, Mar 19, 2013 at 5:56 PM, Jesse Barnes <jbarnes at virtuousgeek.org> wrote:
>> > I think it just needs to be a low level call to crtc disable on each
>> > pipe, otherwise we'll zap the state we're trying to save.
>>
>> That just reminded me that we also should restore the right dpms state
>> I think. At least I'm not too sure whether we'll currently do that
>> (and whether the modeset state tracker would catch it). Otoh dpms
>> standby/suspend died with gen4 ;-)
>
> Hm yeah haven't tested that at all.  One typical kind of suspend will
> happen after DPMS off when the machine has been idle for some period.
> When it comes back up the user will probably want to see the display.
> But we don't have to enforce that on the kernel side; we can leave it
> to userspace.

Note that this isn't about dpms state in general, we'll take care of
that. The problem is with intermediate dpms levels, which requires us
to keep the pipe partially running. If you force-restore such a thing
we'll end up at dpms ON. Which isn't quite what we want.

Otoh it's old hw, so I don't think we need to spill too many brain
cycles on this issue. But if we do fix it, I think we should implement
proper support to read out that hw state and cross-check it -
otherwise it's pretty much guaranteed to be broken.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch