[Bug 110954] USB Type-C monitor flashes once when play a video file after unplug and re-plug the monitor

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110954

--- Comment #9 from Nathan Ciobanu <nathan.d.ciobanu at linux.intel.com> ---
Created attachment 145081
  --> https://bugs.freedesktop.org/attachment.cgi?id=145081&action=edit
dmesg marked with "play audio and flash"

I took another log on a Chromebook with drm-tip and drm.debug=0xe. I also
marked the spot where I start playing the video with "play audio and flash". 

You'll then see the spurious which get printed during the video playback.
[drm:skl_update_scaler] scaler_user index 0.0: staged scaling request for
1920x1080->1724x970 scaler_users = 0x1
[drm:intel_atomic_setup_scalers] Attached scaler id 0.0 to PLANE:31"

It is during the video playback time that the flash occurs.

The one interesting thing I found is that we restart probing for connectors at
this point:
[ 3980.917229] [drm:drm_helper_probe_single_connector_modes]
[CONNECTOR:86:eDP-1]
which is triggered by an ioctl call from user space. For some reason the
userspace needs to reprobe and I'm not sure what causes this. 

Another finding from my previous investigation was that if you wait for the
this reprobing to finish and then play the video the flash will not occur.

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