when not using an external display, I only get a single overrun:

 [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun

This issue only seems to manifest when using modesetting+glamor, when using the intel-driver with SNA I don't get any of these.

Please add drm.debug=0xe to the kernel command line and attach the resulting dmesg.

Created attachment 131815 [details]
syslog with drm.debug=0xe

Still 4.10 based kernel? The dmesg was cut off so I can't tell.

Can you try 4.12 or drm-tip? I'm thinking this may be have been fixed by

commit a5509abda48ecfc133fac6268e83fc1a93dba039
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Fri Feb 17 17:01:59 2017 +0200

    drm/i915: Fix legacy cursor vs. watermarks for ILK-BDW

(In reply to Clemens Eisserer from comment #4)
> Created attachment 131815 [details]
> syslog with drm.debug=0xe
Hello Clemens,
Any update on this case with the kernel suggested by Ville? Could you share please? 
Thank you.

Hi Elisabeth,

I'll give 4.12 a try as soon as it will be rolled out for Fedora 25 (which should be any day now).

I suspect I see the same bug on a Thinkpad T570, newest firmware 1.23..

The glitches are pretty rate, at most a few time a day if at all. Today I noticed [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe A FIFO underrun. I guess I haven't checked dmesg earlier.

On AC power and with a second display, the bug appears basically never. I think I observed it once but I cannot tell for sure whether it was on AC, second display or once. 

I'll try adding drm.debug=0xe.

Forgot to mention that the bug appears significantly more often when using the integrated UMTS modem. I have no clue why this is related. Until now I suspected that the problem is related to power.

Created attachment 133473 [details]
dmesg | grep drm

Log with drm.debug=0xe. 
This underrun happened without UMTS, on AC power but without an external monitor.

This is on kernel 4.12.4.

Thanks for updating.
If more information is needed it will be requested in the comment section below. 
Also changing priority since it's a sporadic issue.

Just experienced:

[ 1222.200551] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun
[ 1222.200626] [drm:intel_pch_fifo_underrun_irq_handler [i915]] *ERROR* PCH transcoder B FIFO underrun


on linux 4.12.8 with 2 monitors active (1x DisplayPort, 1x VGA, internal display disabled).

First of all. Sorry about spam.
This is mass update for our bugs. 

Sorry if you feel this annoying but with this trying to understand if bug still valid or not.
If bug investigation still in progress, please ignore this and I apologize!

If you think this is not anymore valid, please comment to the bug that can be closed.
If you haven't tested with our latest pre-upstream tree(drm-tip), can you do that also to see if issue is valid there still and if you cannot see issue there, please comment to the bug.

Yes, this continues to be a problem.  I tried both the drm-tip and the backported kernel in the Ubuntu 18.04 daily.   Both kernels still show the bug.

OK, thanks for confirming.

Reporter, do you still have the issue?
Please try to reproduce the issue using drm-tip (https://cgit.freedesktop.org/drm-tip) and kernel parameters drm.debug=0x1e log_buf_len=4M, and if the problem persists attach the full dmesg from boot.

Paulo, testing with latest drm-tip will help the situation?

Clemens, Do you still have the issue?
If so, can you attach dmesg from latest drm-tip for investigation. 
No feedback from few months, reducing the priority to medium.

I still experience the issue with 4.18.16. I don't have the time to install the latest drm-tip but I'll try to provide a log at least. Unfortunately I don't see the bug very often.

No feedback from more than few months. Closing this issue WORKSFORME.
We need feedback from the drmtip. With no logs from drmtip it's not possible to investigate this issue further. 

Please reopen the issue if it occurs on drmtip.