[Intel-gfx] Power saving using Display port HPD

[Daniel Vetter]

On Mon, Apr 14, 2014 at 11:17:53AM +0300, Imre Deak wrote:
> 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

Iirc we've agreed that when all screens are off it's ok to no longer
support hotplug. Or is this only the case when _only_ the DP port is off
but e.g. another port (edp or mipi) is on?

I'm asking since currently on hsw/bdw hotplug also doesn't work when you
switch everything off ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch