[Intel-gfx] [PATCH] drm/i915/icl: Use hw engine class, instance to find irq handler

[Chris Wilson]

Quoting Daniele Ceraolo Spurio (2018-03-12 15:09:31)
> 
> 
> On 12/03/18 07:52, Chris Wilson wrote:
> > Quoting Mika Kuoppala (2018-03-12 14:41:31)
> >> Interrupt identity register we already read from hardware
> >> contains engine class and instance fields. Leverage
> >> these fields to find correct engine to handle the interrupt.
> >>
> >> add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-160 (-160)
> >> Function                                     old     new   delta
> >> gen11_irq_handler                            764     604    -160
> >> Total: Before=1506953, After=1506793, chg -0.01%
> >>
> >> v2: handle class/instance overflow correctly (Mika)
> >>
> >> Suggested-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >> Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
> >> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> >> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> >> Signed-off-by: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> >> ---
> >>   static void
> >> @@ -2825,12 +2787,28 @@ gen11_gt_irq_handler(struct drm_i915_private * const i915,
> >>                  }
> >>   
> >>                  for_each_set_bit(bit, &intr_dw, 32) {
> >> -                       const u16 iir = gen11_gt_engine_intr(i915, bank, bit);
> >> +                       const u32 ident = gen11_gt_engine_identity(i915,
> >> +                                                                  bank, bit);
> >> +                       const u16 iir = ident & GEN11_INTR_ENGINE_MASK;
> >> +                       u8 class, instance;
> >> +                       struct intel_engine_cs *engine;
> >>   
> >>                          if (unlikely(!iir))
> >>                                  continue;
> > 
> > Now if (!ident) or actually just use u32 iir as we can pass it straight
> > through to cs_irq_handler.
> 
> Can't use (!ident) here because bit 31 (iir valid) or the class/instance 
> bits might be set when the iir is empty (because we had a buffered irq 
> that we actually already handled).

If there's a valid bit, surely that's the one we want to be testing?

If the low iir bits are 0, that's fine. The question is whether it's
common enough to worry about; and I note it's marked as unlikely() so
it seems like we can just let it fallthrough and do nothing.
-Chris