On Wed, Mar 12, 2014 at 07:21:45PM -0700, Ben Widawsky wrote:
> On Thu, Mar 13, 2014 at 01:40:28AM +0000, Damien Lespiau wrote:
> > While wandering in the spec, I noticed that BDW removes those 2 bits
> > from INSTPM. I couldn't find any direct way to invalidate the TLB (ie
> > without the ring working already). Maybe someone will be more lucky.
> >
> > At least, we now know we may be a problem.
> >
> > Signed-off-by: Damien Lespiau <damien.lespiau@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/intel_ringbuffer.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > index c50388a..4eb3e06 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> > @@ -981,8 +981,14 @@ void intel_ring_setup_status_page(struct intel_ring_buffer *ring)
> > I915_WRITE(mmio, (u32)ring->status_page.gfx_addr);
> > POSTING_READ(mmio);
> >
> > - /* Flush the TLB for this page */
> > - if (INTEL_INFO(dev)->gen >= 6) {
> > + /*
> > + * Flush the TLB for this page
> > + *
> > + * FIXME: These two bits have disappeared on gen8, so a question
> > + * arises: do we still need this and if so how should we go about
> > + * invalidating the TLB?
> > + */
> > + if (INTEL_INFO(dev)->gen >= 6 && INTEL_INFO(dev)->gen < 8) {
> > u32 reg = RING_INSTPM(ring->mmio_base);
> >
> > /* ring should be idle before issuing a sync flush*/
>
> I'm missing something on the original patch,
> 884020bf3d2a3787a1cc6df902e98e0eec60330b. How were we emitting
> breadcrumbs without flushing the TLB? All bathcbuffers should be
> bookended by a TLB invalidate already, so I'm not sure the logic holds.
> Chris could explain that one a bit further?
>
> The only reason I bring this up is I'd like to rip this out completely
> and have Thiago retest, or at least change the comment/commit message to
> be to reflect whatever light Chris sheds on the matter.
>
> Anyway, the bits are definitely gone, and I also can't find a non-ring
> based replacement.
> Reviewed-by: Ben Widawsky <ben@xxxxxxxxxxxx>
Queued for -next, thanks for the patch.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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