[Intel-gfx] [PATCH] drm/i915/gen4: Fix interrupt setup ordering

[Adam Jackson]

On Thu, 2010-05-27 at 17:26 -0400, Adam Jackson wrote:
> Unmask, then enable interrupts, then enable interrupt sources; matches
> PCH ordering.  The old way (sources, enable, unmask) gives a window
> during which interrupt conditions would appear in ISR but would never
> reach IIR and thus never raise an IRQ.  Since interrupts only trigger
> on rising edges in ISR, this would lead to conditions where (for
> example) output hotplugging would never fire an interrupt because it
> was already stuck on in ISR.
> 
> Also, since we know IIR and PIPExSTAT have been cleared during
> irq_preinstall, don't clear them again during irq_postinstall, nothing
> good can come of that.
> 
> Signed-off-by: Adam Jackson <ajax at redhat.com>

Just to follow up, I've tested this (combined with the already-merged
VGA paranoia patch) on GM45.  Output hotplug still works and I'm no
longer seeing stuck bits in ISR.

- ajax
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