[Bug 104934] New: Sometimes does not detect 60Hz Full HD mode for external display, switching to 60 Hz with interlace

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104934

            Bug ID: 104934
           Summary: Sometimes does not detect 60Hz Full HD mode for
                    external display, switching to 60 Hz with interlace
           Product: DRI
           Version: unspecified
          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: Martin at Lichtvoll.de
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 137163
  --> https://bugs.freedesktop.org/attachment.cgi?id=137163&action=edit
Xorg log with what I believe is todays output

On Linux 4.15.0-tp520-btrfstrim+ (4.15 + a small patch to fix BTRFS SSD
trimming, compiled with gcc 7.3.0 for full generic retpoline) on a ThinkPad
T520 with Intel Sandybridge graphics sometimes on rebooting or also after a
resume from hibernate to disk or suspend to RAM the external 24 inch Fujitsu
P24T-7 LED display connected via ThinkPad Minidock display port shows the
screen with visible flickering.

In this case xrandr shows:

DP-3 connected 1920x1080+1920+0 (normal left inverted right x axis y axis)
531mm x 299mm
   1920x1080i    60.00*   50.00    59.94  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08  

When disconnecting the DisplayPort cable and reconnecting it or with
disconnecting the laptop from the dock and putting it back on it, Intel DRM/KMS
eventually recognizes again that the display and cable are capable of doing
1920x1080 with 60 Hz. After switching the resolution via Plasma´s
Systemsettings or directly via xrandr this looks like:

DP-3 connected 1920x1080+1920+0 (normal left inverted right x axis y axis)
531mm x 299mm
   1920x1080     60.00 +  50.00    50.00    59.94  
   1920x1080i    60.00*   50.00    59.94  
   1680x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    60.00  
   800x600       75.00    60.32  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    60.00    59.94  
   720x400       70.08 


I am testing meanwhile with the third DisplayPort cable, which should be able
to even transfer UltraHD 4K resolutions.

Some kernel and X.org releases back this issue never happened. I did not report
it immediately as its again a "it happens sometimes" issue with no clear
pattern to reproduce it.

In the failure case I usually see nothing in dmesg. Today I saw:

[191597.165942] [drm:intel_set_pch_fifo_underrun_reporting [i915]] *ERROR*
uncleared pch fifo underrun on pch transcoder B
[191597.165952] [drm:cpt_irq_handler [i915]] *ERROR* PCH transcoder B FIFO
underrun

I don´t know whether this is related.

I attach a trimmed Xorg.0.log with what I believe is todays output.



Some hardware information:

% inxi -v1 
System:    Host: merkaba Kernel: 4.15.0-tp520-btrfstrim+ x86_64 bits: 64
Console: tty 6
           Distro: Debian GNU/Linux buster/sid
CPU:       Dual core Intel Core i5-2520M (-MT-MCP-) speed/max: 845/3200 MHz
Graphics:  Card: Intel 2nd Generation Core Integrated Graphics Controller
           Display Server: X.Org 1.19.6 driver: modesetting Resolution:
1920x1080 at 60.00hz, 1920x1080 at 60.00hz
           OpenGL: renderer: Mesa DRI Intel Sandybridge Mobile version: 3.3
Mesa 17.3.3
Drives:    HDD Total Size: 780.2GB (58.8% used)
Info:      Processes: 348 Uptime: 5 days Memory: 4809.4/15825.4MB Client: Shell
(zsh) inxi: 2.3.56

% phoronix-test-suite system-info
[…]
  GRAPHICS:           Intel Sandybridge Mobile 1536MB (1300MHz)
    OpenGL:           3.3 Mesa 17.3.3
    Display Driver:   modesetting 1.19.6
    Monitor:          P24T-7 LED
    Screen:           3840x1080
[…]

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