Bug#867555: gnome-shell: Tries to drive monitor at unsupported refresh rate

[Simon McVittie]

On Fri, 07 Jul 2017 at 11:02:59 +0100, Mark Brown wrote:
> A recent upgrade on my system appears to have caused GNOME to drive one
> of my monitors at an unsupported refresh rate after login (gdm is fine).
> After login my primary display goes into power saving mode though GNOME
> appears to think it's fine.  Changing my GNOME session to Wayland caused
> the monitor to display an error message about the unsupported refresh
> rate, I am able to use the monitor if I lower the refresh rate.

This seems weird. The gdm greeter is itself a GNOME-on-Wayland session
(unless you have reconfigured it, in which case it might be a GNOME-on-X11
session) so I would expect it to behave the same as your GNOME-on-Wayland
login, or possibly your GNOME-on-X11 login.

The fact that it doesn't suggests that there might be some problem with
your saved display settings (so, specific to your uid).

> This may not be a bug in gnome-shell but I don't know which package is
> responsible.  Both GNOME and X got upgrades.

This is probably not directly gnome-shell's fault, given that it hasn't
been updated since April. I don't know what caused this, so all I can
do at the moment is ask for more information and point you in some
likely directions.

My first question is, what graphics hardware and driver is this?

The kernel, libdrm, Mesa and any proprietary graphics drivers that you
might be using are possible components to blame. Did any of those
get upgraded around the same time? (apt logs are likely to be useful
information.)

X11 might be implicated, but since you have a similar issue in Wayland and
xorg-server's recent changelog only lists some targeted security fixes,
that's probably not the first one to try.

gnome-settings-daemon is another possible culprit (I think it's
involved in display configuration for X11?) but looking at its
recent changelog, that seems unlikely.

Selectively downgrading recently-upgraded packages would also be
helpful to pin down which package is responsible.

Other things you could try:

* Run xrandr --verbose (X11 only, not useful in Wayland)

* There should be a way to get the same information as from xrandr in
  Wayland, but I don't know it; other GNOME or graphics-stack maintainers
  might?

* Move your ~/.config/monitors.xml out of the way (don't delete it; if
  this works, it would be useful to see what's in it). This is where
  GNOME stores display settings. You could also compare it with
  ~/.config/monitors.xml~ which is the second-most-recent version.

* Look for mentions of EDID, DDC or mode in the Xorg log
  (could be /var/log/Xorg.*.log, ~/.cache/gdm/* or the systemd Journal
  depending how your X server was started)

I hope this helps,
    S