vga_switcheroo: MIS-using the DIS command on a muxless system

[Lukas Wunner]

On Fri, Jan 19, 2018 at 08:38:20AM +0100, Enrico Mioso wrote:
> I forgot one last question. Is there any way I can force the system
> to switch to the ATI card without installing a graphical environment,
> just out of curiosity?

As you've observed correctly, your particular machine isn't capable of
muxing the display, it's a muxless model.  Nowadays a mux is only found
on MacBook Pros  (can switch at runtime) and a few gaming laptops (can
only switch in BIOS).

On supported (i.e., pre-retina) MacBook Pros, it is indeed possible to
switch to the discrete GPU without a graphical environment, in fact
no graphical environment is even allowed to run currently.

If by "force the system to switch" you're not referring to muxing the
display but rather exercising (and thus powering on) the discrete GPU,
I believe you do need a graphical environment to start a client with
DRI_PRIME.  Failing that, you can try to force the GPU out of runtime
suspend with "echo on > /sys/bus/pci/devices/0000:01:00.0/power/control".
(Use "echo auto" to re-enable automatic power management.)

Kind regards,

Lukas