[Bug 97157] MST displays fail to wake

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=97157

            Bug ID: 97157
           Summary: MST displays fail to wake
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: dan.doel@gmail.com

Created attachment 125450
  --> https://bugs.freedesktop.org/attachment.cgi?id=125450&action=edit
dmesg output

Since moving to kernel 4.6, I've been having regular problems with my MST
monitors failing to wake after being put to sleep. This only seems to occur
after the machine has been on for a sufficient amount of time, but I usually
experience it within a day of booting, and typically after the displays have
been powered off for an extended period of time.

There are two MST monitors, but typically only one fails to wake. Also, it is
more often that the secondary display is the one that fails. However, I have
had the primary display fail to come back (while the secondary one succeeds),
and I have had both fail to come back as well.

Sometimes, only a complete power off is able to make the monitors wake up; a
reboot is not always sufficient.

The dmesg displays some errors, and I've poked around a bit. It seems likely
that this is related to commit f3d58dccdbf9f8c0a229d555d4b295d52e743039, which
was first included in 4.6. This commit basically causes dpms to work at all
with MST monitors; before it was a no-op that didn't actually put the monitors
into power saving. That doesn't help narrow the problem down much, though,
since a significant portion of the mst dpms code probably wasn't being
exercised before that.

Also, it seems notable that the error message (which seems more like a debug
message) in the STANDBY/SUSPEND/OFF case keeps reporting higher numbers, as
though it keeps going through the ON case, which increments the variable, but
not making it through the portion of the OFF case that decrements the variable.

I'll attach dmesg journal output that might be relevant. I believe the
error/debug messages timestamped 'Jul 31 11:03:49' correspond to the first time
one of the displays failed to wake up. I tried various ways of toggling the
dpms off and on after that, so those are the subsequent error messages in the
log.

As far as specs go, I have:
  Radeon HD7870 (Pitcairn)
  Kernel 4.6.4 (4.6.3 also affected)
  2 UP2414Q mst displays
  xorg-server 1.18.4
  Modesetting driver

Let me know if there's any more information I can try to provide.

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