Workaround for bug 702953?

[Adam Williamson]

On Mon, 2011-05-16 at 14:27 +0200, Christof Damian wrote:
> On Mon, May 16, 2011 at 12:47, Matej Cepl <mcepl at redhat.com> wrote:
> > Dne 14.5.2011 23:23, Andreas Tunek napsal(a):
> >> If I understand correctly, my computer (2011 27 inch iMac) has an
> >> integrated intel GPU, but Fedora is using the Radeon GPU. Is there any
> >> way what GPU you use? I did not find any documentation regarding this,
> >> but maybe I looked at the wrong places?
> >
> > With Thinkpad T400 (ATI/Intel dual graphics) I could theoretically (it's
> > broken on my machine) switch the GPU in BIOS. There is almost certainly
> > nothing in Linux drivers to do so.
> 
> I can switch GPUs in my T510 with switcheroo, which is included in
> Fedora already.
> 
> See: http://en.gentoo-wiki.com/wiki/Vga_switcheroo and
> http://christof.damian.net/2010/11/fedora-14-on-lenovo-thinkpad-t510.html?showComment=1291238658612#c255706088919254379
> 
> Not sure if this applies to the iMac

Doing it in the BIOS, if possible, I would expect to be more reliable
and probably also more efficient. All implementations differ slightly,
but usually if you have an option to 'lock' one card in the BIOS, it
will completely disable the other; this is how it works on my Sony Vaio
Z. This probably saves power as the other chipset is completely
disabled, and makes things rather simpler for the kernel and X because
they don't have to handle two chipsets at all, the system just looks
like a perfectly normal, single-chipset one.

I've also observed before that, if you can manage it, disabling the
'faster' chipset and using the Intel one permanently is almost always
going to be the best approach on Linux, because the proprietary drivers
don't work with these systems and the free drivers for the Radeon and
NVIDIA chipsets are likely to be slower and buggier than the ones for
the Intel chipsets, even if the Radeon/NVIDIA chips are _theoretically_
more powerful. So there's just about nothing to gain from trying to use
them as 'intended' - running with the Radeon/NVIDIA chip will probably
only make the system buggier, hotter, slower, and more power-hungry.
IMBW, but my take is it's best to try and find a way to lock the system
into the Intel chipset, and just use that; and that's usually going to
be in the BIOS.

(For my Sony, I had to hack the BIOS to expose the necessary option;
this is pretty well documented in various forums. I don't know about
Macs.)
-- 
Adam Williamson
Fedora QA Community Monkey
IRC: adamw | Fedora Talk: adamwill AT fedoraproject DOT org
http://www.happyassassin.net