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[Launchpad Bug Tracker <1308105@xxxxxxxxxxxxxxxxxx>]

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[Impact]

 * When a TV is power-cycled, it is no longer detected as an available display.
 
 * The root issue is in xfce4-settings: xfsettingsd.
 
 * The related patch correctly handles the NULL mode the TV enters when powered off.

[Test Case]

 * Connect a TV to a computer running xfce4-settings 4.12.0, this can be in a single configuration or dual-monitor.
 
 * Power the TV off.
 
 * Power the TV on.
 
 * Expected: TV powers on and remains connected as an available display.
 
 * Actual: TV powers on and is not connected or detected.

[Regression Potential]

 * Regression potential is minimal: The associated patch targets this
very specific scenario and behavior, and does not interact with the rest
of the codebase.

[Original Report]
I had an HTPC with Mythbuntu 12.04 installed. Upon upgrading a new behavior that if the TV is power cycled it no longer detects a link with the HTPC.

When this happens I can find in the xorg log that there is an
accompanying log item:

[ 39829.509] (II) NVIDIA(0): Setting mode "NULL"

After debugging with NVIDIA at
https://devtalk.nvidia.com/default/topic/729955/linux/tv-stops-being-
detected/ we've deteremined it's a X client that reacts to the RANDR
events causing the mode to be set to NULL.

Working through the list in an Xfce environment, the culprit is
xfsettingsd. If xfsettingsd is running, it causes the TV to come up in a
NULL mode. If it's killed, it remains in the mode it was previously
running in.

Until this is fixed, this behavior can be worked around with a simple shell script:
==============================
#!/bin/sh
#Fix TV state when HDMI link is lost.
#By Mario Limonciello <superm1@xxxxxxxxxx>

OUTPUT="HDMI-0"
BAD_MODE="1280x720"
GOOD_MODE="1920x1080"

for MODE in $BAD_MODE $GOOD_MODE; do
 DISPLAY=:0 xrandr --output $OUTPUT --mode $MODE
 sleep 2
done
==============================

** Affects: ubuntu-translations
     Importance: Medium
         Status: Confirmed

** Affects: xfce4-settings
     Importance: Critical
         Status: Fix Released

** Affects: xfce4-settings (Ubuntu)
     Importance: Undecided
         Status: Fix Released

** Affects: xfce4-settings (Ubuntu Xenial)
     Importance: Undecided
         Status: Fix Committed

** Affects: xfce4-settings (Ubuntu Bionic)
     Importance: Undecided
         Status: Fix Released


** Tags: dist-upgrade downstream patch verification-needed verification-needed-xenial xenial
-- 
[SRU] Xfce resets TV mode to NULL when power cycled
https://bugs.launchpad.net/bugs/1308105
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