[Spice-devel] [video-qxl 2/2] Default to only one head, not 4.

[Hans de Goede]

Hi,

Note I'm currently working on a related problem, which I plan
to fix in a way which interacts with patch 1 of this series.

See:
https://bugzilla.redhat.com/show_bug.cgi?id=894421

And specifically:
https://bugzilla.redhat.com/show_bug.cgi?id=894421#c7

Actually let me copy and paste that comment here for
easier reading / discussion:

"""
(In reply to comment #5)
 > Ah, ok I can reproduce now. To reproduce this requires:
 > 1) open a second display
 > 2) In gnome-display-settings do;
 >  1) select 1280x768 => apply
 >  2) select 1280x760 => apply
 >  3) select 1280x768 => apply

Ok, so what is happening here is the following:

1) When making changes on a *dual* monitor setup gnome-display-settings calls
XRRGetScreenResources rather then XRRGetScreenResourcesCurrent, causing a
call to xf86-video-qxl's modelist update function

2) xf86-video-qxl's modelist update function function gives a modelist for the monitor with
all standard modes from the rom header + the current mode with the preferred mode flag set

3) What happens now is:

a) Running at 1280x768, modelist is standard + preferred 1280x768, lets call this modelist1
b) change mode to 1280x760, gnome-settings-daemon remembers this as the user-selected mode for the monitor with modelist1
c) modelist gets updated, gnome-settings-daemon now sees a modelist of standard + preferred 1280x760, sees this as a new monitor with modelist2
d) change mode to 1280x768, gnome-settings-daemon remembers this as the user-selected mode
     for the monitor with modelist2
e) modelist gets updated, gnome-settings-daemon now sees a modelist of standard + preferred 1280x768, sees this as the return of the monitor with modelist1, has a user set mode of 1280x760 for this
f) gnome-settings-daemon changes to the user set mode for this monitor of 1280x760
g) modelist gets updated, gnome-settings-daemon now sees a modelist of standard + preferred 1280x760, sees this as the return of the monitor with modelist2, has a user set mode of 1280x768 for this
f) gnome-settings-daemon changes to the user set mode for this monitor of 1280x768, goto
    e) and loop infinitely

I propose to fix this by not adding the current-mode as preferred mode. Instead always set 1024x768 as preferred mode to stop the initial mode too big problem for which the patch, adding the setting the current-mode as preferred mode, was added.
"""

BTW reading patch 1 again, I wonder what exactly it tries to solve, since
currently when using spice with qemu (no experience with x-spice) you can
already set modes > 1024x768 without problems.

Regards,

Hans