[Intel-gfx] Power saving using Display port HPD

[Imre Deak]

On Mon, 2014-04-14 at 09:47 +0200, Daniel Vetter wrote:
> On Mon, Apr 14, 2014 at 9:43 AM, Arun Chandran <achandran at mvista.com> wrote:
> > 1)  Revert the commit 77961eb984c7e5394bd29cc7be2ab0bf0cc7e7b1.
> > With this commit DP hotplug events are not coming after doing "xset dpms
> > force off"
> >
> > commit bfcbf45b5b458ebdc38118ca67279a1cd90e085d
> > Author: Arun Chandran <achandran at mvista.com>
> > Date:   Fri Apr 11 16:16:32 2014 +0530
> >
> >     Revert "drm/i915: power domains: add vlv power wells"
> >
> >     This reverts commit 77961eb984c7e5394bd29cc7be2ab0bf0cc7e7b1.
> 
> So this breaks DP hotplug detection? Imre?

Yes, unfortunately. I made this clear in my patchset [1] and it was also
discussed on IRC. If there isn't any (e)DP,HDMI pipe active we power
down the DPIO HW block responsible normally for DP and HDMI hotplug
detection.

There is one possible solution: the pin that is used for HPD detection
can be used either normally in the above way, where it's controlled by
the DPIO block, or as a GPIO where it's controlled by the GPIO HW block
which is on even if we power down the DPIO. So during power down periods
we could reconfigure that pin to work as a GPIO and treat any interrupts
arriving it as an HPD event. I haven't had yet time to investigate this.

Another way is to turn on polling while powered down. This would also
make VGA hotplug work, for which we don't have a GPIO alternative as
above.

[1] 
http://lists.freedesktop.org/archives/intel-gfx/2014-February/040232.html

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