Re: [PATCH] drm/i915/gen8+: Init/reset display interrupts only if i915 IRQs are enabled

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On Thu, Sep 28, 2017 at 01:01:34PM +0100, Chris Wilson wrote:
> Quoting Imre Deak (2017-09-28 12:59:16)
> > On Thu, Sep 28, 2017 at 11:18:27AM +0100, Chris Wilson wrote:
> > > Quoting Imre Deak (2017-09-28 11:06:24)
> > > > Only init / reset the display interrupts during power well enabling /
> > > > disabling if the i915 interrupts are enabled. So far we did the
> > > > init / reset during driver loading / resuming too, where
> > > > initialization / enabling of the i915 interrupts happens only at a later
> > > > point. This didn't cause a problem due to GEN8_MASTER_IRQ_CONTROL being
> > > > cleared, but triggered gen3_assert_iir_is_zero() in GEN8_IRQ_INIT_NDX().
> > > > 
> > > > References: https://bugs.freedesktop.org/show_bug.cgi?id=102988
> > > > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx>
> > > 
> > > Patch makes sense, so
> > > Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > 
> > Thanks.
> > 
> > > 
> > > There's an irq powerwell! When is it taken? We don't take it for GT as
> > > far as I am aware (we should for execlists plus whenever we enable the
> > > user interrupt). Should we?
> > 
> > Only the display interrupt registers have a power well that we toggle
> > from the driver (display power well/power well 2). The rest of interrupt
> > regs including the GT ones are backed by a power well that the HW/DMC FW
> > toggles automatically (always-on power well/power well 0). So no need to
> > take it explicitly; there is the slow-down problem where the context
> > restore during such enabling by DMC adds overhead, which will be solved
> > by Tvrtko's WA.
> 
> For that w/a can we make the powerwell request more explicit? Instead of
> POWERWLL_MODESET maybe POWERWELL_GT_IRQ?

Yes, sounds good to have a power domain for this purpose.

--Imre

> -Chris
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