[Bug 111701] PSR causes graphical glitches on Dell XPS 15 9570

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111701

--- Comment #16 from Sultan Alsawaf <sultan at kerneltoast.com> ---
> Compared your patch with mine, the result of both should be the same, did
> you spot any difference?
> I'm sure that other developers will not like this manual string comparison
> too.
It's not the same because your patch does not adhere to the EDID specification.
According to the EDID standard
(https://en.wikipedia.org/wiki/Extended_Display_Identification_Data#Display_Descriptors),
the 13 bytes of text for the display descriptor are terminated with a line feed
character when the length of the content is less than 13 bytes (it's not
terminated with a zero byte, which is what your strncmp assumes). My panel
model string is less than 13 bytes ("TK6R7"), but my EDID is malformed and the
model string is terminated with a 0x80 character. So in my patch, I made
panel_in_psr2_blacklist() interpret any !isgraph character as a terminating
character, which is what the edid-decode tool does as well.

Here's the raw dump of my EDID for you to see:
00000000: 00 ff ff ff ff ff ff 00 4d 10 9a 14 00 00 00 00  ........M.......
00000010: 04 1c 01 04 a5 22 13 78 0e de 50 a3 54 4c 99 26  .....".x..P.TL.&
00000020: 0f 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01  .PT.............
00000030: 01 01 01 01 01 01 ac 37 80 a0 70 38 3e 40 30 20  .......7..p8>@0 
00000040: 35 00 58 c2 10 00 00 18 00 00 00 00 00 00 00 00  5.X.............
00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 fe 00 54  ...............T
00000060: 4b 36 52 37 80 4c 51 31 35 36 4d 31 00 00 00 00  K6R7.LQ156M1....
00000070: 00 02 41 03 28 00 12 00 00 0a 01 0a 20 20 00 2b  ..A.(.......  .+

> Running Ubuntu 18.10 with drm-tip kernel on a Whiskey Lake reference
> platform, all GEN9 are very similar on display so I should be able to
> reproduce it if I had the exactly same panel model as you.
I'm running Ubuntu 19.10 with drm-tip. Try using that, and then change the
login screen background to make the glitch much easier to see. To change the
login screen background, run this long command:
sudo perl -i -p0e 's,(#lockDialogGroup.*?)},#lockDialogGroup {\nbackground:
#2c001e
url(file:///usr/share/backgrounds/Staniel_Cay_by_Joseph_Bylund.jpg);\nbackground-repeat:
no-repeat;\nbackground-size: cover;\nbackground-position: center;\n},s'
/usr/share/gnome-shell/theme/gdm3.css

Then keep rebooting until you see the glitch in my video, assuming your setup
is affected.

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