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"Broadcast RGB" property doesn't always appear

Sometimes (maybe half a dozen times per year, yeah, the worst kind of bug) when using external screen, "Broadcast RGB" xrandr property doesn't appear, and the output is stuck in 16:235 mode. Reproduction steps are unknown. dmesg doesn't have anything weird in it. Reconnecting screen, docking-undocking laptop, suspending-resuming don't seem to help. Reboot did fix the issue.

Compare xrandr --prop outputs, broken and normal (other properties are missing, too):

DP-2-2 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 531mm x 298mm
	EDID:
		00ffffffffffff0009d11e7f45540000
		2617010380351e782e9de1a654549f26
		0d5054a56b80d1c0457c617c818081bc
		953c317c0101023a801871382d40582c
		4500132a2100001e000000ff00593944
		3030353737534c300a20000000fd0038
		901ea021000a202020202020000000fc
		0042656e5120786c32343131740a0162
		02010400fe5b80a07038354030203500
		132a2100001a866f80a0703840403020
		3500132a2100001afc7e808870381240
		18203500132a2100001e000000000000
		00000000000000000000000000000000
		00000000000000000000000000000000
		00000000000000000000000000000000
		000000000000000000000000000000c7
	non-desktop: 0
		supported: 0, 1
   1920x1080     60.00*+  59.94
   1280x1024    119.96    75.02    60.02
   1440x900     119.85
   1152x864      75.00
   1024x768     119.99    75.03    60.00
   832x624       74.55
   800x600      119.97    75.00    60.32
   640x480       75.00    60.00    59.94
   720x400       70.08
DP-2-2 connected 1920x1080+1366+0 (normal left inverted right x axis y axis) 531mm x 298mm
	EDID:
		00ffffffffffff0009d11e7f45540000
		2617010380351e782e9de1a654549f26
		0d5054a56b80d1c0457c617c818081bc
		953c317c0101023a801871382d40582c
		4500132a2100001e000000ff00593944
		3030353737534c300a20000000fd0038
		901ea021000a202020202020000000fc
		0042656e5120786c32343131740a0162
		02010400fe5b80a07038354030203500
		132a2100001a866f80a0703840403020
		3500132a2100001afc7e808870381240
		18203500132a2100001e000000000000
		00000000000000000000000000000000
		00000000000000000000000000000000
		00000000000000000000000000000000
		000000000000000000000000000000c7
	max bpc: 12
		range: (6, 12)
	Broadcast RGB: Full
		supported: Automatic, Full, Limited 16:235
	audio: auto
		supported: force-dvi, off, auto, on
	link-status: Good
		supported: Good, Bad
	CONNECTOR_ID: 112
		supported: 112
	non-desktop: 0
		range: (0, 1)
   1920x1080     60.00*+  59.94
   1280x1024    119.96    75.02    60.02
   1440x900     119.85
   1152x864      75.00
   1024x768     119.99    75.03    60.00
   832x624       74.55
   800x600      119.97    75.00    60.32
   640x480       75.00    60.00    59.94
   720x400       70.08

I would debug it the next time it happens if you could give me some clues where to look.

  • x86_64
  • Linux 5.10.15-gentoo (Gentoo patchset is very small, so it's essentially vanilla)
  • Gentoo Linux
  • ThinkPad T440, Intel Core i3-4010U
  • DVI connector at the dock station (though I'm sure I had this with with builtin miniDP + HDMI adapter before)
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