drm/i915: Don't emit mbox updates without semaphores

Aside from the fact that it leaves confusing dumps on error capture, it
is entirely unnecessary, and potentially harmful in cases like BDW,
where the instruction has changed.

In reality (seemingly), this will have no behavioral impact.

Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e05a0216cd9b..b106984c722a 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -663,14 +663,15 @@ gen6_add_request(struct intel_ring_buffer *ring)
         struct drm_device *dev = ring->dev;
         struct drm_i915_private *dev_priv = dev->dev_private;
         struct intel_ring_buffer *useless;
-        int i, ret;
+        int i, ret, num_dwords = 4;
 
-        ret = intel_ring_begin(ring, ((I915_NUM_RINGS-1) *
-                                      MBOX_UPDATE_DWORDS) +
-                                      4);
+        if (i915_semaphore_is_enabled(dev))
+                num_dwords += ((I915_NUM_RINGS-1) * MBOX_UPDATE_DWORDS);
+#undef MBOX_UPDATE_DWORDS
+
+        ret = intel_ring_begin(ring, num_dwords);
         if (ret)
                 return ret;
-#undef MBOX_UPDATE_DWORDS
 
         for_each_ring(useless, dev_priv, i) {
                 u32 mbox_reg = ring->signal_mbox[i];