[Bug 100765] New: [SKL] DPMS: Samsung monitor turns on and off every few seconds when it should be off

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100765

            Bug ID: 100765
           Summary: [SKL] DPMS: Samsung monitor turns on and off every few
                    seconds when it should be off
           Product: DRI
           Version: DRI 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: freedesktop at kheafield.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 130992
  --> https://bugs.freedesktop.org/attachment.cgi?id=130992&action=edit
dmesg with drm.debug=0x1e log_buf_len=1M

-- system architecture: x86_64
-- kernel version: 4.11.0-rc7+ (from drm-tip commit
bc781a3cf9a80e4c5ed0d47fd0c67923bcfcdf2c), same happens with 4.10.11
-- Linux distribution: Gentoo
-- Machine or mother board model: Gigabyte Z170X-Gaming 7 rev 1.0 (includes
Alpine Ridge) and Intel(R) Core(TM) i7-6700 CPU @ 3.40GHz
-- Display connector: DP
-- Monitor: Samsung LU28E590DS/EN

When the monitor is meant to be off with DPMS, it instead alternates between
backlight off and backlight on every few seconds.  When the backlight is on,
the monitor's OSD says "DisplayPort" in the top left as if it's just been
connected.  

If done from X with "xset dpms force off", the screen is black except for the
"DisplayPort" indicator.  If done from the console with "setterm -blank force",
then the console appears when the backlight alternates to on.  This is not
caused by input; it works fine with HDMI.  

Experiments:

Motherboard    | Distro       | Connection       | Monitor | Result
Z170X-Gaming 7 | Gentoo       | DisplayPort      | Samsung | Alternates
Z170X-Gaming 7 | Gentoo       | USBC->DisplayPort| Samsung | Alternates
Z170X-Gaming 7 | Gentoo       | HDMI 2.0         | Samsung | Correct
Z170X-Gaming 7 | Gentoo       | DisplayPort->DVI | Sceptre | Correct
Z170X-Gaming 7 | Gentoo       | USBC->VGA        | Sceptre | Correct
Z170X-UD5 TH   | Ubuntu 16.10 | USBC->DisplayPort| Samsung | Correct

USBC connection means the Thunderbolt Type C port with an adapter.    

The baseline monitor is a Sceptre X24WG-1080P with VGA and DVI inputs.  

Alternates is the problem that the monitor backlight turns on and off every few
seconds.  Correct means the backlight stays off.  

Relevant piece of xrandr --verbose:

DP3 connected 3840x2160+0+0 (0x4a) normal (normal left inverted right x axis y
axis) 610mm x 350mm
        Identifier: 0x45
        Timestamp:  32595
        Subpixel:   unknown
        Gamma:      1.0:1.0:1.0
        Brightness: 1.0
        Clones:     HDMI2
        CRTC:       0
        CRTCs:      0 1 2
        Transform:  1.000000 0.000000 0.000000
                    0.000000 1.000000 0.000000
                    0.000000 0.000000 1.000000
                   filter: 
        EDID: 
                00ffffffffffff004c2d4d0c46584d30
                2a1a0104b53d23783a5fb1a2574fa228
                0f5054bfef80714f810081c08180a9c0
                b300950001014dd000a0f0703e803020
                35005f592100001a000000fd00384b1e
                873c000a202020202020000000fc0055
                3238453539300a2020202020000000ff
                00485450484130353539360a20200142
                02030ef041102309070783010000023a
                801871382d40582c45005f592100001e
                565e00a0a0a02950302035005f592100
                001a04740030f2705a80b0588a005f59
                2100001e000000000000000000000000
                00000000000000000000000000000000
                00000000000000000000000000000000
                00000000000000000000000000000052
        Broadcast RGB: Automatic 
                supported: Automatic, Full, Limited 16:235
        audio: auto 
                supported: force-dvi, off, auto, on
        link-status: Good 
                supported: Good, Bad
  3840x2160 (0x4a) 533.250MHz +HSync -VSync *current +preferred
        h: width  3840 start 3888 end 3920 total 4000 skew    0 clock 133.31KHz
        v: height 2160 start 2163 end 2168 total 2222           clock  60.00Hz

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