It seems to have no adverse effect, that I have noticed anyway. Reproduces reliably. [drm:intel_dp_start_link_train] *ERROR* failed to enable link training [drm:intel_dp_complete_link_train] *ERROR* failed to start channel equalization [drm:ivybridge_set_fifo_underrun_reporting] *ERROR* uncleared fifo underrun on pipe A [drm:ivb_err_int_handler] *ERROR* Pipe A FIFO underrun This is with an Intel NUC (Haswell) on Ubuntu.
Please boot with "drm.debug=0xe" as a Kernel parameter (you can pass it from Grub), reproduce the bug, then run "dmesg > dmesg.txt" and attach the file here.
Created attachment 107832 [details] dmesg
Created attachment 107833 [details] xorg
I have debugged the problem a bit further. It turns out a certain order of events is necessary to trigger the bug (or at least that's the most reliable way to reproduce). First, suspend. Next my monitor goes into standby, and after a few minutes turns itself off. Now, wake from suspend. Turn on monitor. If the last two events are reversed, the error does not appear.
What kernel version was that? please boot next time with buf_log_len=8M so we have full dmesg. Could you please try to reproduce with latest drm-intel-nightly from cgit.freedesktop.org/drm-intel. Well since you use Ubuntu one good alternative is ppa's drm-intel-nightly kernel: http://kernel.ubuntu.com/~kernel-ppa/mainline/drm-intel-nightly/current/
That's the complete log with 3.16, just with drm grepped. I tried drm-intel-nightly, the fifo underrun error is missing. Just this. [ 195.451488] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to enable link training [ 195.454207] [drm:intel_dp_complete_link_train [i915]] *ERROR* failed to start channel equalization
*** This bug has been marked as a duplicate of bug 86478 ***
Closing as duplicate of closed+fixed.
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