drm/i915: Push EMIT_INVALIDATE at request start to backends

Move the common engine->emit_flush(EMIT_INVALIDATE) back to the backends
(where it was once previously) as we seek to specialise it in future
patches.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181207090213.14352-1-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 3a47a47..a9084a5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1276,17 +1276,20 @@ static int execlists_request_alloc(struct i915_request *request)
 
 	GEM_BUG_ON(!request->hw_context->pin_count);
 
-	/* Flush enough space to reduce the likelihood of waiting after
+	/*
+	 * Flush enough space to reduce the likelihood of waiting after
 	 * we start building the request - in which case we will just
 	 * have to repeat work.
 	 */
 	request->reserved_space += EXECLISTS_REQUEST_SIZE;
 
-	ret = intel_ring_wait_for_space(request->ring, request->reserved_space);
+	/* Unconditionally invalidate GPU caches and TLBs. */
+	ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
 	if (ret)
 		return ret;
 
-	/* Note that after this point, we have committed to using
+	/*
+	 * Note that after this point, we have committed to using
 	 * this request as it is being used to both track the
 	 * state of engine initialisation and liveness of the
 	 * golden renderstate above. Think twice before you try