I believe that i just found a temporary workaround.
Since the flickering seems to be caused by the automatic mode detection
on my non-connected VGA output, I used xrandr to force a mode on that
output.
I used the following commands
xrandr --newmode dummy 75.00 1280 1301 1333 1408 800 804 808 816 -hsync -vsync
xrandr --addmode VGA dummy
xrandr --output VGA --mode dummy
Those commands cause a lot of flickering but after them, flickering is gone.
The result can be verified with
$ xrandr --prop | cat -n
1 Screen 0: minimum 320 x 200, current 1280 x 800, maximum 1280 x 1280
2 VGA disconnected 1280x800+0+0 (normal left inverted right x axis y
axis) 0mm x 0mm
3 dummy 65.3*
4 LVDS connected 1280x800+0+0 (normal left inverted right x axis y axis)
261mm x 163mm
5 EDID_DATA:
6 00ffffffffffff0006af142100000000
7 010f0103801a10780a30259855548827
8 24505400000001010101010101010101
9 0101010101014c1d0080502010301520
10 440005a3100000190000000000000000
11 00000000000000000001000000fe0057
12 35333832004231323145570a000000fe
13 00fffdf3e9bb8d6f0001010a2020005f
14 PANEL_FITTING: full
15 supported: center full_aspect full
16 BACKLIGHT_CONTROL: native
17 supported: native legacy combination
kernel
18 BACKLIGHT: 0 (0x00000000) range: (0,0)
19 1280x800 65.3*+
20 1024x768 60.0
21 800x600 60.3
22 640x480 59.9
23 TV disconnected (normal left inverted right x axis y axis)
24 BOTTOM: 37 (0x00000025) range: (0,100)
25 RIGHT: 46 (0x0000002e) range: (0,100)
26 TOP: 36 (0x00000024) range: (0,100)
27 LEFT: 54 (0x00000036) range: (0,100)
28 TV_FORMAT: NTSC-M
29 supported: NTSC-M NTSC-443 NTSC-J PAL-M
30 PAL-N PAL
The interesting line is 3 which indicates that my "dummy" mode is activated for
the VGA output.
PS: I used a 1280x800 mode because this is the resolution of my laptop
panel and, somehow, using a smaller resolution caused my gnome panels to
be resized.
--
Flickering with version 2.4.0
https://bugs.launchpad.net/bugs/256142
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