Re: [PATCH] virtio-gpu: Respect graphics update interval for EDID

[Gerd Hoffmann <kraxel@redhat.com>]

  Hi,

> > Because of the wasted frames I'd like this to be an option you can
> > enable when needed.  For the majority of use cases this seems to be
> > no problem ...
> 
> I see blinks with GNOME on Wayland on Ubuntu 20.04 and virtio-gpu with
> the EDID change included in this patch.

/me looks closely at the patch again.

So you update the edid dynamically, each time the refresh rate changes.
Problem with that approach is software doesn't expect edid to change
dynamically because on physical hardware it is static information about
the connected monitor.

So what the virtio-gpu guest driver does is emulate a monitor hotplug
event to notify userspace.  If you resize the qemu window on the host
it'll look like the monitor with the old window size was unplugged and
a new monitor with the new window size got plugged instead, so gnome
shell goes adapt the display resolution to the new virtual monitor size.

The blink you are seeing probably comes from gnome-shell processing the
monitor hotplug event.

We could try to skip generating a monitor hotplug event in case only the
refresh rate did change.  That would fix the blink, but it would also
have the effect that nobody will notice the update.

Bottom line:  I think making the edid refresh rate configurable might be
useful, but changing it dynamically most likely isn't.

take care,
  Gerd