[Bug 102035] [BAT][BXT] kernel BUG at drivers/gpu/drm/i915/intel_lrc.c:604!

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=102035

--- Comment #2 from Chris Wilson <chris at chris-wilson.co.uk> ---
Hitting the same assertion on bxt/gem_concurrent_blit, always has a trail of
breadcrumbs like:

[   61.964007] bcs0(3): 0+ rq.seqno=2275 [ctx=91], count=1
[   61.964050] bcs0(1): [3/3] status=1
[   61.964096] bcs0(1): 0+ rq.seqno=2276 [ctx=91], count=2
[   61.964180] bcs0(1): [4/4] status=8002
[   61.964189] bcs0(1): - rq.seqno=2276 [ctx=91], status=8002, count=2
[   61.977615] bcs0(1): [5/5] status=18
[   61.977640] bcs0(1): - rq.seqno=2276 [ctx=91], status=18, count=1
[   61.995341] bcs0(2): 0+ rq.seqno=2277 [ctx=9b], count=1
[   61.995427] bcs0(2): 0+ rq.seqno=2278 [ctx=9b], count=2
[   61.995623] bcs0(1): [0/1] status=1
[   61.995786] bcs0(1): [1/1] status=8002
[   61.995802] bcs0(1): - rq.seqno=2278 [ctx=9b], status=8002, count=2
[   62.008366] bcs0(1): [2/2] status=18
[   62.008391] bcs0(1): - rq.seqno=2278 [ctx=9b], status=18, count=1
[   62.020052] bcs0(0): 0+ rq.seqno=2279 [ctx=8c], count=1
[   62.020142] bcs0(0): 0+ rq.seqno=2280 [ctx=8c], count=2
[   62.020207] bcs0(1): [3/4] status=12
[   62.020219] bcs0(1): - rq.seqno=2280 [ctx=8c], status=12, count=2

^ This is the bogus event. 0x12 == COMPLETE | PREEMPTED, but it is following
the ACTIVE->IDLE notification, where we always expect the IDLE->ACTIVE
(status=1) afterwards (see examples above). Following the bogus 0x12 wakeup,
the context-switch notification never "catches up", i.e. we never see the final
context-switch of ELEMENT_SWITCH or IDLE. At that point only a reset seems to
cure it.

[   62.020228] bcs0(1): [4/4] status=8002
[   62.020235] bcs0(1): - rq.seqno=2280 [ctx=8c], status=8002, count=1
[   62.024699] bcs0(3): 1+ rq.seqno=2281 [ctx=96], count=1
[   62.024724] bcs0(3): 0+ rq.seqno=2280 [ctx=8c], count=2
[   62.024753] bcs0(1): [5/5] status=8002
[   62.024774] bcs0(1): - rq.seqno=2280 [ctx=8c], status=8002, count=2


Now, answers on a postcard what we are meant to do to this prevent heading into
this cul-de-sac.

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