[Bug 97264] [BDW] Screen blanking (DP link reset?) when working in terminals

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97264

--- Comment #7 from Timo Kalliomäki <timoka10 at gmail.com> ---
Hi,

I seem to be having the same problem with the i7-5600U Dell E7450 (BIOS A13,
MST firmware 3.10.1) and Dell P2175Q rev. A03 display (MST off, DDC/CI off).
For me, the reproduction steps are:

1. Output picture to both internal monitor and external DP-linked one
(everything is OK if only the external or only the internal one is in use)
2. Set external monitor to a large resolution, eg. 3840x2160 at 60Hz,
3840x2160 at 30Hz, 2560x1440 (1920x1080 seems to not exhibit this behavior but I
did not test for an extended period)
3. Bring mouse cursor to external screen and position it over a window
(everything is OK as long as cursor is kept on internal monitor)
4. Give focus to the window from step 3 (this seems to vary by program; Firefox
being the program getting focus does not cause problems, but eg. Konsole or
Kate does)
5. Press a key on the keyboard (even Ctrl alone will do)
=> maybe half the time, the key press causes the external monitor losing signal
for a second or so. Signal loss confirmed via observing the monitor OSD.

The problem was present both in the 4.8 kernels of Kubuntu 16.10, as well as
4.9.2 and 4.9.6 of Debian Stretch.

The drm_atomic messages always show up in dmesg on step 5, but they seem
similar to me for both problematic and unproblematic cases.

No signal loss:
[  588.715676] [drm:drm_atomic_state_init [drm]] Allocated atomic state
ffffa0692aab3800
[  588.715701] [drm:drm_atomic_get_plane_state [drm]] Added [PLANE:29:cursor B]
ffffa06a09f02180 state to ffffa0692aab3800
[  588.715719] [drm:drm_atomic_get_crtc_state [drm]] Added [CRTC:30:pipe B]
ffffa06a0bbae800 state to ffffa0692aab3800
[  588.715733] [drm:drm_atomic_set_crtc_for_plane [drm]] Link plane state
ffffa06a09f02180 to [NOCRTC]
[  588.715744] [drm:__drm_atomic_helper_disable_plane [drm_kms_helper]] Set
[NOFB] for plane state ffffa06a09f02180
[  588.715758] [drm:drm_atomic_check_only [drm]] checking ffffa0692aab3800
[  588.715801] [drm:intel_plane_atomic_calc_changes [i915]] [CRTC:30:pipe B]
has [PLANE:29:cursor B] with fb -1
[  588.715832] [drm:intel_plane_atomic_calc_changes [i915]] [PLANE:29:cursor B]
visible 1 -> 0, off 1, on 0, ms 0
[  588.715853] [drm:drm_atomic_commit [drm]] commiting ffffa0692aab3800
[  588.715896] [drm:drm_atomic_state_default_clear [drm]] Clearing atomic state
ffffa0692aab3800
[  588.715915] [drm:drm_atomic_state_free [drm]] Freeing atomic state
ffffa0692aab3800
[  588.723720] [drm:drm_mode_addfb2 [drm]] [FB:87]
[  588.747072] [drm:drm_mode_addfb2 [drm]] [FB:90]

Signal loss:
[  609.115830] [drm:drm_atomic_state_init [drm]] Allocated atomic state
ffffa06a065a1000
[  609.115864] [drm:drm_atomic_get_plane_state [drm]] Added [PLANE:29:cursor B]
ffffa069d18d9840 state to ffffa06a065a1000
[  609.115891] [drm:drm_atomic_get_crtc_state [drm]] Added [CRTC:30:pipe B]
ffffa06a08582000 state to ffffa06a065a1000
[  609.115911] [drm:drm_atomic_set_crtc_for_plane [drm]] Link plane state
ffffa069d18d9840 to [NOCRTC]
[  609.115928] [drm:__drm_atomic_helper_disable_plane [drm_kms_helper]] Set
[NOFB] for plane state ffffa069d18d9840
[  609.115953] [drm:drm_atomic_check_only [drm]] checking ffffa06a065a1000
[  609.116016] [drm:intel_plane_atomic_calc_changes [i915]] [CRTC:30:pipe B]
has [PLANE:29:cursor B] with fb -1
[  609.116062] [drm:intel_plane_atomic_calc_changes [i915]] [PLANE:29:cursor B]
visible 1 -> 0, off 1, on 0, ms 0
[  609.116095] [drm:drm_atomic_commit [drm]] commiting ffffa06a065a1000
[  609.116154] [drm:drm_atomic_state_default_clear [drm]] Clearing atomic state
ffffa06a065a1000
[  609.116177] [drm:drm_atomic_state_free [drm]] Freeing atomic state
ffffa06a065a1000
[  609.124994] [drm:drm_mode_addfb2 [drm]] [FB:87]
[  609.148166] [drm:drm_mode_addfb2 [drm]] [FB:90]

Also, on boot I get the message
kernel: [drm:gen8_irq_handler [i915]] *ERROR* CPU pipe B FIFO underrun

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