[Intel-gfx] [PATCH] drm/i915/execlists: Unshadow MI_USER_INTERRUPT

[Chris Wilson]

Quoting Chris Wilson (2019-05-02 10:41:19)
> Given an immediate preemption event on re-enabling arbitration
> (MI_ARB_ON_OFF | MI_ARB_ENABLE) it appears that the HW may forget about
> the ongoing MI_USER_INTERRUPT, losing the interrupt in the process. If
> we happen to be waiting on that interrupt at the time, the system may
> then grind to a halt.
> 
> My presumption is that there is an effective shadow inside the CS as it
> parses and buffers the commands, and if we push the MI_USER_INTERRUPT
> out of the immediate parse buffer it is not lost by the arbitration
> check.
> 
> Testcase: igt/gem_concurrent_blit
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
> Plausible? I need a few hours to confirm my hunch.

Sadly, it got stuck again.
-Chris