From ed4596ea992db45a27bfc3a0e401fb95ef2d5f23 Mon Sep 17 00:00:00 2001 From: Akash Goel Date: Tue, 25 Oct 2016 22:05:23 +0530 Subject: [PATCH] drm/i915/guc: WA to address the Ringbuffer coherency issue Driver accesses the ringbuffer pages, via GMADR BAR, if the pages are pinned in mappable aperture portion of GGTT and for ringbuffer pages allocated from Stolen memory, access can only be done through GMADR BAR. In case of GuC based submission, updates done in ringbuffer via GMADR may not get committed to memory by the time the Command streamer starts reading them, resulting in fetching of stale data. For Host based submission, such problem is not there as the write to Ring Tail or ELSP register happens from the Host side prior to submission. Access to any GFX register from CPU side goes to GTTMMADR BAR and Hw already enforces the ordering between outstanding GMADR writes & new GTTMADR access. MMIO writes from GuC side do not go to GTTMMADR BAR as GuC communication to registers within GT is contained within GT, so ordering is not enforced resulting in a race, which can manifest in form of a hang. To ensure the flush of in-flight GMADR writes, a POSTING READ is done to GuC register prior to doorbell ring. There is already a similar WA in i915_gem_object_flush_gtt_write_domain(), which takes care of GMADR writes from User space to GEM buffers, but not the ringbuffer writes from KMD. This WA is needed on all recent HW. v2: - Use POSTING_READ_FW instead of POSTING_READ as GuC register do not lie in any forcewake domain range and so the overhead of spinlock & search in the forcewake table is avoidable. (Chris) Cc: Chris Wilson Signed-off-by: Sagar Arun Kamble Signed-off-by: Akash Goel Reviewed-by: Chris Wilson Signed-off-by: Chris Wilson Link: http://patchwork.freedesktop.org/patch/msgid/1477413323-1880-1-git-send-email-akash.goel@intel.com --- drivers/gpu/drm/i915/i915_guc_submission.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c index bf65ffa7e4ce..74235ea3950f 100644 --- a/drivers/gpu/drm/i915/i915_guc_submission.c +++ b/drivers/gpu/drm/i915/i915_guc_submission.c @@ -634,6 +634,7 @@ static int guc_ring_doorbell(struct i915_guc_client *gc) */ static void i915_guc_submit(struct drm_i915_gem_request *rq) { + struct drm_i915_private *dev_priv = rq->i915; unsigned int engine_id = rq->engine->id; struct intel_guc *guc = &rq->i915->guc; struct i915_guc_client *client = guc->execbuf_client; @@ -641,6 +642,11 @@ static void i915_guc_submit(struct drm_i915_gem_request *rq) spin_lock(&client->wq_lock); guc_wq_item_append(client, rq); + + /* WA to flush out the pending GMADR writes to ring buffer. */ + if (i915_vma_is_map_and_fenceable(rq->ring->vma)) + POSTING_READ_FW(GUC_STATUS); + b_ret = guc_ring_doorbell(client); client->submissions[engine_id] += 1; -- 2.20.1