drm/i915/ringbuffer: EMIT_INVALIDATE after switch context

The recommend procedure was to switch contexts (and mm) then invalidate
the TLBs. Make it so.
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/20181207090213.14352-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1827,12 +1827,12 @@ static int ring_request_alloc(struct i915_request *request)
 	 */
 	request->reserved_space += LEGACY_REQUEST_SIZE;
 
-	/* Unconditionally invalidate GPU caches and TLBs. */
-	ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
+	ret = switch_context(request);
 	if (ret)
 		return ret;
 
-	ret = switch_context(request);
+	/* Unconditionally invalidate GPU caches and TLBs. */
+	ret = request->engine->emit_flush(request, EMIT_INVALIDATE);
 	if (ret)
 		return ret;