[Bug 91393] [bdw edp] Screen Flickering

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91393

--- Comment #44 from flux242 <flux242 at gmail.com> ---
(In reply to flux242 from comment #43)
> hi, I'm also experiencing bad flickering of my laptop screen.
> I have installed xubuntu 15.10 on Acer C740:
> 
> a at chrome:~$ sudo lshw -c video
>   *-display               
>        description: VGA compatible controller
>        product: Broadwell-U Integrated Graphics
>        vendor: Intel Corporation
>        physical id: 2
>        bus info: pci at 0000:00:02.0
>        version: 08
>        width: 64 bits
>        clock: 33MHz
>        capabilities: msi pm vga_controller bus_master cap_list rom
>        configuration: driver=i915 latency=0
>        resources: irq:43 memory:e0000000-e0ffffff memory:d0000000-dfffffff
> ioport:1800(size=64)
> 
> a at chrome:~$ uname -a
> Linux chrome 4.2.0-19-generic #23-Ubuntu SMP Wed Nov 11 11:39:30 UTC 2015
> x86_64 x86_64 x86_64 GNU/Linux
> 
> But today display was blanked after 15 minutes of inactivity and when I
> woken it up I saw no more flickering and this kernel message:
> Dec  5 10:16:48 chrome kernel: [ 3708.390613] [drm:intel_dp_start_link_train
> [i915]] *ERROR* failed to enable link training
> 
> please suggest a way (usingn a kernel parameter) to disable link training
> until a bugfix is backported

I need to add some additional info. Ive managed to reproduce the case when
after screen blanking there's no flickering anymore. I start the 'xset dpms
force off' command to blank the screen and after a pause I press a button to
wake it up. Below is a pastebin when flickering persist after waking up:
http://pastebin.com/fuY57tMH

And here is a pastebin when the flickering is gone after waking up:
http://pastebin.com/4gGMTycL

It was really difficult to reproduce the case when the flicker is gone

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