[ubuntu-x] Hybrid graphics detection

[Christopher James Halse Rogers]

On Thu, 2011-11-03 at 08:50 -0700, Bryce Harrington wrote:
> On Thu, Nov 03, 2011 at 11:44:14AM -0400, Christopher James Halse Rogers wrote:
> > On Thu, 2011-11-03 at 06:52 -0700, Bryce Harrington wrote:
> > > On Thu, Nov 03, 2011 at 09:29:02AM -0400, Christopher James Halse Rogers wrote:
> > > > > > 
> > > > > > However, we talked about powering off the discrete card as well. My
> > > > > > recollection is that the X team was planning to look into that, but
> > > > > > there are unknowns about how and when we can do that.
> > > > > 
> > > > > Chris was given a system that exhibits this problem, so we've had a
> > > > > chance to review it as well.  We've spoken to the kernel team about the
> > > > > issue and I think a fix should be forthcoming down the pike.  Chris can
> > > > > fill in mroe.
> > > > 
> > > > Simply writing "OFF" to /sys/kernel/debug/vgaswitcheroo/switch will turn
> > > > off the unconnected GPU on the system I've been playing with - and cuts
> > > > idle power consumption by > 50%.
> > > > 
> > > > For this particular system this is entirely safe - the radeon card isn't
> > > > hooked up to any outputs at all, so if the radeon driver is loaded then
> > > > the radeon card is useless.  The switcheroo interface only exists when
> > > > radeon is loaded, so unconditionally writing "OFF" to it *on this
> > > > system* is the right thing to do.
> > > 
> > > Would it make sense to make that into a udev rule?
> > 
> > I'm not sure that a udev rule would have the necessary context, but
> > either a udev rule or an upstart script would absolutely make sense.
> 
> Would any context be needed beyond loaded kernel gfx driver(s) and
> machine identification info?

I don't believe so, no.  But if we're writing a udev rule that needs to
be triggered on a udev event, and I'm not sure whether there's a udev
event that we can rely on to happen at an appropriate time.

Right?
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