[ubuntu-x] Hybrid graphics detection

Christopher James Halse Rogers raof at ubuntu.com
Thu Nov 3 13:29:02 UTC 2011

On Wed, 2011-11-02 at 21:35 -0700, Bryce Harrington wrote:
> On Wed, Nov 02, 2011 at 06:00:18PM -0400, Evan Broder wrote:
> > To briefly summarize the session, we felt that we couldn't present any
> > "true" hybrid graphics support (any sort of GPU switching, dynamic or
> > otherwise) to non-power users within the scope of Precise, so we
> > wanted to focus on not making it possible to use your hardware at all
> > under the standard configuration.
> > 
> > The issue I'm concerned about is that with most hybrid graphics
> > hardware configurations, the OS sees multiple GPUs, and most of the
> > tools assume there will only be one.
> > 
> > For example, if you have nVidia Optimus, Jockey sees an nVidia GPU,
> > and installs the nvidia-current driver. That changes your default
> > libGL. When you reboot, and the Intel GPU is connected to the outputs,
> > the nVidia libGL doesn't work with the Intel driver.
> Finally we got our hands on one of these systems, and already it's
> fixed, and even SRU'd to oneiric:  #885204
> If anyone is on oneiric and has this hardware, you can help by
> enabling oneiric-proposed, uninstall nvidia, update to the fixed jockey,
> verify it no longer recommends nvidia, and comment either way on the bug
> report.
> https://bugs.launchpad.net/ubuntu/+source/jockey/+bug/885204
> > > As you understand I am not an expert on the issue, just recently got
> > > my hands on some of these hybrid GPU laptops. To me the biggest
> > > problem, and one that actually makes Linux unusable for many users
> > > (those who know even less than me and actually use it on the go), is
> > > that the unused card is running full power.
> > 
> > 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.

> > > And you, our last hope, have *one* system to test on? Can't some
> > > corporate goodness throw a handful of lappies at you?
> It's astounding how effective just having the hardware on hand is.  The
> two systems we've been looking at this week will be going with Chris,
> and the certification team says they'll send me another (which is
> failing some cert tests).
> We've got other higher priority projects this cycle, but we do hope to
> at least knock down some of the main hybrid graphics bugs (like the two
> mentioned above) that are preventing people from using their systems as
> ordinary laptops.  Beyond that, well time will tell.
> Bryce

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