Mutter recently gained the ability to deal with multiple GPUs
rendering at different displays. These GPUs would have a display
connected to them, and Mutter was adapted in order to be aware
of different GPUs and their outputs.
However, one specific edge case appeared: PRIME systems. PRIME
systems have two GPUs:
* The integrated GPU (iGPU), usually Intel, which has connectors
and deals with the routine load.
* The dedicated GPU (dGPU), usually AMD or NVidia, which has no
connectors at all and are there just to aid heavy loads.
On those systems, the dGPU is aggressively put to sleep by the
kernel to avoid energy waste. Waking it up is a costly operation.
With Mutter's adaptation to deal with multiple GPUs, Mutter began
wakening the dGPU every time some rendering had to be done. This
was causing stuttering every time the dGPU was put to sleep, and
Mutter asked it to wake up again.
To fix this situation, this commit ignores GPUs with no connectors
attached.
Issue: #77
When drmHandleEvent() returns an error and errno is set to EAGAIN,
instead of ending up in a busy loop, poll() the fd until there is
anything to read.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
In order to eventually support multilpe GPUs with their own connectors,
split out related meta data management (i.e. outputs, CRTCs and CRTC
modes) into a new MetaGpu GObject.
The Xrandr backend always assumes there is always only a single "GPU" as
the GPU is abstracted by the X server; only the native backend (aside
from the test backend) will eventually see more than one GPU.
The Xrandr backend still moves some management to MetaGpuXrandr, in
order to behave more similarly to the KMS counterparts.
https://bugzilla.gnome.org/show_bug.cgi?id=785381
