[coreboot] T420 Optimus/NVIDIA GPU support

[Patrick Rudolph]

On 2016-06-26 07:25 AM, Intel Miner wrote:
> Hi everyone,
> 
> Apologies if this is the wrong place to ask about this, but
> 
> I'm eyeing off buying a Lenovo T420 ThinkPad, specifically one with the
> NVIDIA GPU, with "Optimus" support
> 
> The information I can dig up on the initial support says that the NVIDIA
> GPU models are NOT supported by Coreboot
> 
> However I see in the hybrid_graphics.c file that there's a listing for the
> "T420/T520" (the T520 seemingly /does/ support the NVIDIA GPU?)
> 
> I can't seem to find any up-to-date information either way regarding the
> GPU status in the T420 however. Any information regarding this would be
> appreciated :)
> 
> (Alternatively I could just purchase one, build Coreboot and try, of
> course!)

Hi !
Latest coreboot does support Nvidia GPUs on all Txx models, but it
doesn't support Optimus.
The hybrid_graphics is for switching display panel to the selected GPU
on Optimus muxed laptops.
At the moment you can choose to use one of the GPUs at boot time! The
other one will be disabled.
In theory you could use both GPU at the same time using DRI_PRIME (with
latest HEAD),
but it will use much more power, as Optimus isn't supported, and the
Nvidia GPU is always active.

What's missing to implement Nvidia Optimus:
* ACPI for panel switching on "muxed" devices
* ACPI for power switching on all devices

Regards,
Patrick