[Intel-gfx] Blanking out when driving QHD 2560x1440 cheap panels with the displayport

[Rubin Abdi]

Originally posted this to the Linux on Thinkpad list. A friend
recommended I try here instead.

I have an X220, I am running Debian Sid, 3.12.9. I've used this machine
to drive 27" and larger Dell displays at full resolution via displayport
to displayport and displayport to dual link DVI without issue.

A few months ago I purchased one of those $400 Apple knock off S-IPS
displays from Korea through ebay, branded as Crossover at QHD 2560x1440.
I spent the following month trying to figure out why when driving the
display through my machine's displayport, it would blank out after about
a minute or two of constant action on the screen (like playing a video).
It would go into blank/sleep mode for a second or two, bounce back, do
this a few times before the display giving up and stating there is
nothing turn on/plugged into the displayport and shut off. I tried 3
different displayport cables and assumed the issue wasn't my laptop
since I was driving a different 30" display at the office over
displayport just fine.

Talking with the person who sold me the panel, they mailed over a couple
different boards to swap out inside the display, none of which provided
any improvement. All that came to an end when I realized a month had
passed since I purchased the display and the seller stopped returning my
messages through ebay as their obligation to provide me with support
ended with my inability to leave them bad feedback.

Since then I learned I could drive the monitor through displayport to
dual link DVI (with an attached adapter that sucks in power over USB). I
don't get the show stopping screen blanking issue, but about once every
5 minutes of action on the screen (like scrolling a web page), all the
pixels on the screen vibrate together about 200px back and forth
horizontally for half a second. I decided that was tolerable and a
better option than simply trashing the $400 paper weight.

Yesterday I was thinking of purchasing a replacement display of a
similar design (hoping it wouldn't be as defective) from a retailer over
Amazon at about the same cost, and using this one sitting on my desk as
a display for movies to drive over HDMI at a lower 1080p resolution
which doesn't cause the same symptoms, and place it somewhere else in my
house.

After price searching a little bit, I decided to try a new test before
finally calling it quits and ordering this new monitor. I plugged in an
older Mac Mini I had laying around to the display and started playing a
movie at full resolution. Surprisingly after 30 minutes of driving the
thing over displayport I saw no issues. Swapped the cables, no issues
again. Pulling out an old drive containing a Windows bootable partition
for gaming, I tested out using my X220 with Windows driving the display
through displayport, and to my amazement no issues cropped up.

So why is Linux sucking at providing this display clean signal over the
displayport?

Through the suggestion of this thread...

https://bbs.archlinux.org/viewtopic.php?id=175868

...I've stuck xorg into UXA mode. That's slightly helped as it takes
slightly longer before the display craps about, but by a minute or two.
Other than that thread and attached bug I really haven't seen any other
references of folks having this problem. And it doesn't seem like events
happening to the displayport (such as a monitor blanking) don't end up
in any logs I've found, so debugging this hasn't really happened.

Any thoughts, ideas, or suggestions would be greatly appreciated. Thanks.


00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core
Processor Family Integrated Graphics Controller (rev 09) (prog-if 00
[VGA controller])
	Subsystem: Lenovo Device 21da
	Flags: bus master, fast devsel, latency 0, IRQ 52
	Memory at f0000000 (64-bit, non-prefetchable) [size=4M]
	Memory at e0000000 (64-bit, prefetchable) [size=256M]
	I/O ports at 4000 [size=64]
	Expansion ROM at <unassigned> [disabled]
	Capabilities: <access denied>
	Kernel driver in use: i915


Running stock Debian kernel, no magic kernel options. Running
laptop-mode-tools but it's disabled since I'm plugging in at my desk
with power.

-- 
Rubin
rubin at starset.net

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