Quoting Ville Syrjälä (2018-02-02 17:44:58)
> On Fri, Feb 02, 2018 at 05:31:57PM +0000, Chris Wilson wrote:
> > I think we're okay with just using the master IIR for IRQ_NONE /
> > IRQ_HANDLED as that is the interrupt generator aiui. If the child
> > sources disagree that's another issue, but as far as the kernel is
> > concerned i915 did generate and handle an interrupt.
> 
> I think that might be the usual way it goes. I guess the IIR clearing is
> racing with the MASTER_IRQ read as AFAIK the MASTER_IRQ status bits aren't
> latched or anything (since we don't have to clear them). So I believe this
> still leaves open a small window where even the MASTER_IRQ has cleared
> itself by the time the irq handler gets around to reading it. So that
> would look like a genuine spurious interrupt even though the GPU did
> raise it for a reason.

I've committed ourselves (for the time being at least) to always
returning IRQ_HANDLED if the master IIR reports an interrupt. Hopefully
I won't regret it :)

Thanks,
-Chris
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