From 0a823e8fd4fd67726697854578f3584ee3a49b1d Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Thu, 8 Nov 2018 08:17:38 +0000 Subject: [PATCH] drm/i915/execlists: Force write serialisation into context image vs execution 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 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 Cc: Mika Kuoppala Cc: Tvrtko Ursulin Acked-by: Mika Kuoppala Link: https://patchwork.freedesktop.org/patch/msgid/20181108081740.25615-1-chris@chris-wilson.co.uk Cc: stable@vger.kernel.org (cherry picked from commit 987abd5c62f92ee4970b45aa077f47949974e615) Signed-off-by: Joonas Lahtinen --- 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 43957bb37a42..37c94a54efcb 100644 --- a/drivers/gpu/drm/i915/intel_lrc.c +++ b/drivers/gpu/drm/i915/intel_lrc.c @@ -424,7 +424,8 @@ 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. @@ -432,6 +433,17 @@ static u64 execlists_update_context(struct i915_request *rq) if (ppgtt && !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(); return ce->lrc_desc; } -- 2.30.2