Re: [PATCH 12/15] drm/i915: Interrupt routing for GuC submission

Daniel Vetter
2015-06-17T12:38:48Z

On Wed, Jun 17, 2015 at 02:22:19PM +0200, Daniel Vetter wrote:
> On Wed, Jun 17, 2015 at 09:20:44AM +0100, Dave Gordon wrote:
> > On 16/06/15 10:24, Chris Wilson wrote:
> > > On Mon, Jun 15, 2015 at 07:36:30PM +0100, Dave Gordon wrote:
> > >> +static void direct_interrupts_to_guc(struct drm_i915_private *dev_priv)
> > >> +{
> > >> + struct intel_engine_cs *ring;
> > >> + int i, irqs;
> > >> +
> > >> + /* tell all command streamers to forward interrupts and vblank to GuC */
> > >> + irqs = _MASKED_FIELD(GFX_FORWARD_VBLANK_MASK, GFX_FORWARD_VBLANK_ALWAYS);
> > >> + irqs |= _MASKED_BIT_ENABLE(GFX_INTERRUPT_STEERING);
> > >> + for_each_ring(ring, dev_priv, i)
> > >> + I915_WRITE(RING_MODE_GEN7(ring), irqs);
> > >> +
> > >> + /* tell DE to send (all) flip_done to GuC */
> > >> + irqs = DERRMR_PIPEA_PRI_FLIP_DONE | DERRMR_PIPEA_SPR_FLIP_DONE |
> > >> + DERRMR_PIPEB_PRI_FLIP_DONE | DERRMR_PIPEB_SPR_FLIP_DONE |
> > >> + DERRMR_PIPEC_PRI_FLIP_DONE | DERRMR_PIPEC_SPR_FLIP_DONE;
> > >> + /* Unmasked bits will cause GuC response message to be sent */
> > >> + I915_WRITE(DE_GUCRMR, ~irqs);
> > >
> > > That's scary since userspace depends on a few more DERRMR events
> > > (wait-for-scanline). Where will they end up?
> > > -Chris
> >
> > This doesn't change any bits in DE_RRMR, or set the VBLANK or SCANLINE
> > bits in the DE_GUCRMR, so those events should be unaffected. The GuC
> > isn't interested in those, only in flip done.
>
> Why does the guc care about flip_done? With atomic it'll get exactly none
> of those, ever ...

Well I forgot that mmio writes also generate interrupts. Still strange
that GuC is interested in this. Would be really interesting to know what
GuC is up to here.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation