Note: support of apple macbookpro laptops with two gpus

[karu.pruun]

DragonFly now includes a preliminary port of linux's vga_switcheroo
and apple_gmux drivers: we support macbookpro laptops that have two
gpus, where one is an intel integrated gpu and the other is either an
nvidia or a radeon gpu.

All you have to do is pull the recent master (as of commit a7d463),
build kernel with this line in the config file

options VGA_SWITCHEROO

and after reboot load the apple_gmux and i915 drivers

> sudo kldload apple_gmux
> sudo kldload i915

Note that you have to load apple_gmux *before* loading i915. When
everything works the two lines can be added to /etc/rc.conf

---
apple_gmux_load="YES"
i915_load="YES"
---

DragonFly currently only uses the integrated intel gpu, the other gpu
is ignored (but not powered off). Support of the other gpu will be
improved in future work. The intel i915 driver in master is quite
stable, I have been running it with no glitches for the last two
weeks.

Cheers

Peeter

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