Noticed while reviewing Matt's atomic wm revert patch that we have fifo underruns pre-existing on this platform. Somehow only happens on this testcase. For context the long-term view: http://benchsrv.fi.intel.com/archive/results/CI_IGT_test/ilk-hp8440p.html
I suppose I missed some other ilk/ibx corner case when trying to fix it all. Sigh.
Got it on basic-flip-vs-modeset also
Also shows intermittently in hang-read-crc-pipe-a and read-crc-pipe-b. c.f. also https://bugs.freedesktop.org/show_bug.cgi?id=93640
Also seen in read-crc-pipe-a-frame-sequence. In fact I think it can happen in pretty much any of the kms_* tests.
Raising priority due to BAT. Another instance: http://benchsrv.fi.intel.com//archive/results/CI_IGT_test/Patchwork_1664/ilk-hp8440p/html/ilk-hp8440p@Patchwork_1664@1/igt@kms_flip@basic-flip-vs-dpms.html
Hopefully fixed now commit 1204d5baa8781a1bf968244bd2b0f15ed861e573 Author: Ville Syrjälä <ville.syrjala@linux.intel.com> Date: Fri Apr 1 21:53:18 2016 +0300 drm/i915: Make sure LP1+ watermarks levels are preserved when going from 1 to 2 pipes
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