loading i915 with two graphics cards

[Francois Tigeot]

On Mon, Jul 18, 2016 at 09:56:57PM +0300, karu.pruun wrote:
> On Sun, Jul 17, 2016 at 12:50 PM, Francois Tigeot <ftigeot at wolfpond.org>
> wrote:
> 
> > > the system (DragonFly 4.5) gets stuck, the screen is frozen at console.
> >
> > The Geforce GT 330M is apparently a mobile device.
> > What is your hardware exactly ? If this is a laptop, it is possible the two
> > GPUs are not independent but use something marketed as "optimus technology"
> > which is currently unsupported by the DragonFly graphics stack.
> 
> Thanks, yes, you're right! It's a laptop, 15" macbookpro (MacBookPro6,2)
> 
> http://www.everymac.com/systems/apple/macbook_pro/specs/macbook-pro-core-i5-2.53-aluminum-15-mid-2010-unibody-specs.html
> 
> And yes, turns out apple have gpu switching:
> 
> http://www.techworld.com/review/laptops/apple-macbook-pro-15-inch-mid-2010-266ghz-core-i7-review-3223803/
> 
> I ran FreeBSD for a test; it gets stuck too. Xorg with linux behaves fine
> though. Xorg log shows two drivers are loaded, nouveau and intel.
> 
> Until DragonFly's grahpics stack gets this feature, I wonder if there's a
> way to switch off one gpu so Xorg will run?

It looks like the macbooks are really special and have their video outputs
connected to a special muxer chip, not directly one or the other GPU.
Linux apparently is able to switch between them with a "vga_switcheroo"
driver:
https://www.phoronix.com/scan.php?page=news_item&px=Linux-MacBook-GPU-Switching

Some people also have tried to write a special EFI firmware driver in order to
permanently disable the NVidia GPU and connect the graphic outputs to the
integrated Intel one:
https://sasanj.wordpress.com/2014/12/03/how-to-turn-off-apple-macbook-pro-discrete-graphics-card-for-linux/

-- 
Francois Tigeot