[Intel-gfx] [PATCH 1/4] drm/i915/gen8: Disable master intr before reading

[Chris Wilson]

Quoting Mika Kuoppala (2018-10-02 15:05:49)
> Disable master interrupt before reading level indications.
> This will close a race where we get a level indication between
> reading and disabling, generating an extra interrupt where we
> could have avoided one.
> 
> Further, as the reading acts also as a post, replace the
> write/post on the irq reset with the helper. On enabling side,
> posting doesn't serve any purpose so it can also be replaced
> with helper.
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>

Proof is in the eating and your experiments have shown that MASTER_IRQ
is not cleared until the sublevels are acked. If it were the opposite
then we would quickly see missed interrupts.

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

Though I would run it through CI a few times before merging just in
case.
-Chris