Re: Graphics pass-through

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2011-05-09 at 13:14 +0200, Jan Kiszka wrote:
> On 2011-05-05 17:17, Alex Williamson wrote:
> >> And what about the host? When does Linux release the legacy range?
> >> Always or only when a specific (!=vga/vesa) framebuffer driver is loaded?
> > 
> > Well, that's where it'd be nice if the vga arbiter was actually in more
> > widespread use.  It currently seems to be nothing more than a shared
> > mutex, but it would actually be useful if it included backends to do the
> > chipset vga routing changes.  I think when I was testing this, I was
> > externally poking PCI bridge chipset to toggle the VGA_EN bit.
> 
> Right, we had to drop the approach to pass through the secondary card
> for now, the arbiter was not switching properly. Haven't checked yet if
> VGA_EN was properly set, though the kernel code looks like it should
> take care of this.
> 
> Even with handing out the primary adapter, we had only mixed success so
> far. The onboard adapter worked well (in VESA mode), but the NVIDIA is
> not displaying early boot messages at all. Maybe a vgabios issue.
> Windows was booting nevertheless - until we installed the NVIDIA
> drivers. Than it ran into a blue screen.

Interesting, IIRC I could never get VESA modes to work.  I believe I
only had a basic VGA16 mode running in a Windows guest too.

> BTW, what ATI adapter did you use precisely, and what did work, what not?

I have an old X550 (rv380?).  I also have an Nvidia gs8400, but ISTR the
ATI working better for me.

> One thing I was wondering: Most modern adapters should be PCIe these
> days. Our NVIDIA definitely is. But so far we are claiming to have it
> attached to a PCI bus. That caps all the extended capabilities e.g.
> Could this make some relevant difference?

The BIOS and early boot use shouldn't care too much about that, but I
could imagine the high performance drivers potentially failing.  Thanks,

Alex