[PATCH] drm/i915: Unconditionally flush any chipset buffers before execbuf

[Chris Wilson <chris@chris-wilson.co.uk>]

If userspace is asynchronously streaming into the batch or other
execobjects, we may not flush those writes along with a change in cache
domain (as there is no change). Therefore those writes may end up in
internal chipset buffers and not visible to the GPU upon execution. We
must issue a flush command or otherwise we encounter incoherency in the
batchbuffers and the GPU executing invalid commands (i.e. hanging) quite
regularly.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=90841
Fixes: 1816f9236303 ("drm/i915: Support creation of unbound wc user...")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Akash Goel <akash.goel@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Tested-by: Matti Hämäläinen <ccr@tnsp.org>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 699315304748..75957aef6219 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -1016,7 +1016,6 @@ i915_gem_execbuffer_move_to_gpu(struct drm_i915_gem_request *req,
 	const unsigned int other_rings = eb_other_engines(req);
 	struct i915_vma *vma;
 	uint32_t flush_domains = 0;
-	bool flush_chipset = false;
 	int ret;
 
 	list_for_each_entry(vma, vmas, exec_list) {
@@ -1029,16 +1028,13 @@ i915_gem_execbuffer_move_to_gpu(struct drm_i915_gem_request *req,
 		}
 
 		if (obj->base.write_domain & I915_GEM_DOMAIN_CPU)
-			flush_chipset |= i915_gem_clflush_object(obj, false);
+			i915_gem_clflush_object(obj, false);
 
 		flush_domains |= obj->base.write_domain;
 	}
 
-	if (flush_chipset)
-		i915_gem_chipset_flush(req->engine->i915);
-
-	if (flush_domains & I915_GEM_DOMAIN_GTT)
-		wmb();
+	/* Unconditionally flush any chipset caches (for streaming writes). */
+	i915_gem_chipset_flush(req->engine->i915);
 
 	/* Unconditionally invalidate GPU caches and TLBs. */
 	return req->engine->emit_flush(req, EMIT_INVALIDATE);
-- 
2.8.1