[Bug 99578] New: [SKL][bisected] Screen regularly returns from power save mode

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99578

            Bug ID: 99578
           Summary: [SKL][bisected] Screen regularly returns from power
                    save mode
           Product: DRI
           Version: XOrg git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: ps at pks.im
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Hi,

Inside of X11, when the screen saver is activated, the monitor turns off
correctly after a short amount of time. But as of recently, the monitor will
turn back on again in regular intervals (roughly every 90 seconds) and then
after a few seconds turn off again.

Some details on my setup: The issue has been surfacing since Linux v4.9. I'll
attach my kernel configuration. I'm using xorg-server-1.19.1 with the built-in
modesetting driver. My hardware includes both an Nvidia Geforce 750Ti (which is
unused and stubbed out via vfio-pci) and an Intel 6600k CPU. There are two
monitors connected to the iGPU, one via Display Port and one via HDMI. The
issue has been occurring on the monitor connected via Display Port, though I
haven't actually checked if the other one behaves similarly. The issue persists
if the HDMI-connected screen is disabled.

As said, the issue started to appear in Linux v4.9 and persists at least until
v4.9.6. I think I also had it occurring on v4.10-rc1, even though I'm not
totally sure here. I've bisected the issue to commit 536ab3ca19ef (drm/i915:
Fix botched merge that downgrades CSR versions., 2016-08-15), which updates the
Intel firmware version to `i915/skl_dmc_ver1_26`. So it seems related to a bug
in the updated firmware.

Reproducing the issue is easy on my computer:

1. Turn the computer on, have the DP display connected
2. `xset s 1` to quickly enable the screen saver
3. Wait a short time span. Usually the bug occurs after roughly 90 seconds
where the screen will turn on again, simply saying "No signal"
4. The screen will turn off again shortly after

I'll attach the bisect log, kernel configuration as well as dmesg. dmesg does
not say anything interesting though as soon as the issue occurs.

Thanks and regards
Patrick

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