Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes: > Ensure that the writes into the context image are completed prior to the > register mmio to trigger execution. Although previously we were assured > by the SDM that all writes are flushed before an uncached memory > transaction (our mmio write to submit the context to HW for execution), > we have empirical evidence to believe that this is not actually the > case. > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108656 I would have marked this also as References. > References: https://bugs.freedesktop.org/show_bug.cgi?id=108315 > References: https://bugs.freedesktop.org/show_bug.cgi?id=106887 > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_lrc.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c > index 22b57b8926fc..f7892ddb3f13 100644 > --- a/drivers/gpu/drm/i915/intel_lrc.c > +++ b/drivers/gpu/drm/i915/intel_lrc.c > @@ -380,7 +380,8 @@ static u64 execlists_update_context(struct i915_request *rq) > > reg_state[CTX_RING_TAIL+1] = intel_ring_set_tail(rq->ring, rq->tail); > > - /* True 32b PPGTT with dynamic page allocation: update PDP > + /* > + * True 32b PPGTT with dynamic page allocation: update PDP > * registers and point the unallocated PDPs to scratch page. > * PML4 is allocated during ppgtt init, so this is not needed > * in 48-bit mode. > @@ -388,6 +389,17 @@ static u64 execlists_update_context(struct i915_request *rq) > if (!i915_vm_is_48bit(&ppgtt->vm)) > execlists_update_context_pdps(ppgtt, reg_state); > > + /* > + * Make sure the context image is complete before we submit it to HW. > + * > + * Ostensibly, writes (including the WCB) should be flushed prior to > + * an uncached write such as our mmio register access, the empirical > + * evidence (esp. on Braswell) suggests that the WC write into memory > + * may not be visible to the HW prior to the completion of the UC > + * register write and that we may begin execution from the context > + * before its image is complete leading to invalid PD chasing. > + */ > + wmb(); Let's put it into use and gather more evidence. Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx> > return ce->lrc_desc; > } > > -- > 2.19.1 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
