Re: [Qemu-devel] emulating a display, instead of just a dumb graphics card

[Gerd Hoffmann <kraxel@redhat.com>]

On Do, 2014-03-27 at 10:57 +0100, Markus Armbruster wrote:
> Olaf Hering <olaf@aepfle.de> writes:
> 
> > Right now qemu does appearently just emulate a graphics card (Cirrus for
> > example), but not an attached monitor/display. The result is confusion
> > in the guest OS. 
> >
> > The current DRM drivers in upstream Linux seem to default to VESA modes.
> > These are either provided by qemu, or Xorg uses a fixed internal list.
> > As a result the VM window is 1280x960. Much too large for my native
> > display.

The kernel has a mode list.  cirrusdrm used to default to the largest
possible video mode, which is stupid and has been fixed meanwhile.  It's
1024x748 now.

> > It seems qemu does not provide a virtual display with valid EDID data.
> > If it would start doing that, the host admin could force a certain
> > display size. Ideally also with proper DPI data.
> >
> > Any idea if thats possible to implement?
> 
> Not an expert in this area, but I can't see why it would be impossible.
> Patches welcome.

qxl can already signal the size of the display(s) to the guest.  Where
"display size" == "spice client window size".  But it doesn't use edid
for that.

Simliar capabilities are planned for virtio-gpu.

Not sure it is possible with cirrus.  The hardware is pretty old, might
be it predates edid ...

stdvga is essentially paravirtual too (when it comes to capabilities
beyond standard vga stuff) and has no interface to communicate preferred
display size or edid blobs to the guest (yet?).

cheers,
  Gerd