[Bug 193500] Interrupt storm after loading i915kms module on Gen4 Intel GPU

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193500

--- Comment #16 from Jan Kokemüller <jan.kokemueller at gmail.com> ---
Created attachment 147363
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=147363&action=edit
ktrdump while loading i915kms (debug.ktr.mask=4)

(In reply to Konstantin Belousov from comment #15)

> So can you describe what the problem is and why your patch help ?

My best guess is that it's some kind of initialization problem regarding the
interrupts, because the behavior stops after a suspend/resume cycle. The
problem started with (or was uncovered by) the opregion code changes. If I stub
out intel_enable_asle the problem goes away. The patch makes it so that
intel_enable_asle gets first called only after I disable/enable the interrupts
of the card. Then there is no interrupt storm anymore. I'll try to debug this
further.

> To see what kind of interrupt causes the storm, compile kernel with KTR_DRM
> and enable ktr(4) tracing for it.

I compiled the kernel with KTR, and enabled KTR_DRM by setting "sysctl
debug.ktr.mask=4". Then I loaded an unpatched i915kms module. I've attached the
log (interesting events are from 34 to 48). It seems only the interrupts on
irq260 are accounted for. Any way I can trace the interrupts on irq16?

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