Moving Closer To NVIDIA Optimus On Linux

David Airlie filed a second DRM pull request over the night for the Linux 3.3 kernel. This second pull has work related to NVIDIA Optimus technology within the Nouveau driver.

In "some fixes for -rc1", David has several DRM-related fixes queued up already for the Linux 3.3 kernel. This comes just days after the main DRM 3.3 pull that brought many enhancements to all of the key open-source kernel graphics drivers.

While this second pull is mostly about fixes, there are two fixes that are prominent if you have a dual-GPU NVIDIA Optimus laptop: "nouveau: properly check for _DSM function support" and "nouveau: Support Optimus models for vga_switcheroo." These patches come from Peter Lekensteyn, an independent contributor.

David says in the pull request, "two nouveau fixes I've
tested locally on optimus laptop and they seem to fix the problem off [sic] turning the GPU off properly when asked."

The commit description by Peter Lekensteyn for the vga_switcheroo support of NVIDIA Optimus says:

Newer nVidia cards with Optimus do not support/use the DSM switching functions. Instead, it require a DSM function to be called prior to bringing a device into D3 state. No other _DSM calls are necessary before/after enabling/disabling a device. Switching between discrete and integrated GPU is not supported by this Optimus _DSM call, therefore return on the switching method.

The other commit is just properly checking for _DSM function support per the ACPI v4.0 specification.

Vga_switcheroo is the rudimentary way of switching between GPUs/drivers on laptops with dual graphics processors. This isn't a seamless transfer but rather requires restarting the X.Org Server, etc. There's also been some other experimental work, but NVIDIA Optimus overall has been a very sore spot on Linux. For now it's recommended to just avoid the hardware.