diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e0c7bf2..7aedc0c 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -666,24 +666,19 @@ static void render_ring_cleanup(struct intel_ring_buffer *ring)
 static int gen6_signal(struct intel_ring_buffer *signaller,
 		       unsigned int num_dwords)
 {
+#define MBOX_UPDATE_DWORDS 3
 	struct drm_device *dev = signaller->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_ring_buffer *useless;
-	int i, ret;
+	int i, ret, num_rings;
 
-	/* NB: In order to be able to do semaphore MBOX updates for varying
-	 * number of rings, it's easiest if we round up each individual update
-	 * to a multiple of 2 (since ring updates must always be a multiple of
-	 * 2) even though the actual update only requires 3 dwords.
-	 */
-#define MBOX_UPDATE_DWORDS 4
-	if (i915_semaphore_is_enabled(dev))
-		num_dwords += ((I915_NUM_RINGS-1) * MBOX_UPDATE_DWORDS);
+	num_rings = hweight32(INTEL_INFO(dev)->ring_mask);
+	num_dwords += round_up((num_rings-1) * MBOX_UPDATE_DWORDS, 2);
+#undef MBOX_UPDATE_DWORDS
 
 	ret = intel_ring_begin(signaller, num_dwords);
 	if (ret)
 		return ret;
-#undef MBOX_UPDATE_DWORDS
 
 	for_each_ring(useless, dev_priv, i) {
 		u32 mbox_reg = signaller->semaphore.mbox.signal[i];
@@ -691,15 +686,13 @@ static int gen6_signal(struct intel_ring_buffer *signaller,
 			intel_ring_emit(signaller, MI_LOAD_REGISTER_IMM(1));
 			intel_ring_emit(signaller, mbox_reg);
 			intel_ring_emit(signaller, signaller->outstanding_lazy_seqno);
-			intel_ring_emit(signaller, MI_NOOP);
-		} else {
-			intel_ring_emit(signaller, MI_NOOP);
-			intel_ring_emit(signaller, MI_NOOP);
-			intel_ring_emit(signaller, MI_NOOP);
-			intel_ring_emit(signaller, MI_NOOP);
 		}
 	}
 
+	/* If num_dwords was rounded, make sure the tail pointer is correct */
+	if (num_rings % 2 == 0)
+		intel_ring_emit(signaller, MI_NOOP);
+
 	return 0;
 }
 
@@ -717,7 +710,11 @@ gen6_add_request(struct intel_ring_buffer *ring)
 {
 	int ret;
 
-	ret = ring->semaphore.signal(ring, 4);
+	if (ring->semaphore.signal)
+		ret = ring->semaphore.signal(ring, 4);
+	else
+		ret = intel_ring_begin(ring, 4);
+
 	if (ret)
 		return ret;
 
@@ -1928,24 +1925,27 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
 		ring->get_seqno = gen6_ring_get_seqno;
 		ring->set_seqno = ring_set_seqno;
-		ring->semaphore.sync_to = gen6_ring_sync;
-		ring->semaphore.signal = gen6_signal;
-		/*
-		 * The current semaphore is only applied on pre-gen8 platform.
-		 * And there is no VCS2 ring on the pre-gen8 platform. So the
-		 * semaphore between RCS and VCS2 is initialized as INVALID.
-		 * Gen8 will initialize the sema between VCS2 and RCS later.
-		 */
-		ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_INVALID;
-		ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_RV;
-		ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_RB;
-		ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_RVE;
-		ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
-		ring->semaphore.mbox.signal[RCS] = GEN6_NOSYNC;
-		ring->semaphore.mbox.signal[VCS] = GEN6_VRSYNC;
-		ring->semaphore.mbox.signal[BCS] = GEN6_BRSYNC;
-		ring->semaphore.mbox.signal[VECS] = GEN6_VERSYNC;
-		ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+		if (i915_semaphore_is_enabled(dev)) {
+			ring->semaphore.sync_to = gen6_ring_sync;
+			ring->semaphore.signal = gen6_signal;
+			/*
+			 * The current semaphore is only applied on pre-gen8
+			 * platform.  And there is no VCS2 ring on the pre-gen8
+			 * platform. So the semaphore between RCS and VCS2 is
+			 * initialized as INVALID.  Gen8 will initialize the
+			 * sema between VCS2 and RCS later.
+			 */
+			ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_INVALID;
+			ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_RV;
+			ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_RB;
+			ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_RVE;
+			ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
+			ring->semaphore.mbox.signal[RCS] = GEN6_NOSYNC;
+			ring->semaphore.mbox.signal[VCS] = GEN6_VRSYNC;
+			ring->semaphore.mbox.signal[BCS] = GEN6_BRSYNC;
+			ring->semaphore.mbox.signal[VECS] = GEN6_VERSYNC;
+			ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+		}
 	} else if (IS_GEN5(dev)) {
 		ring->add_request = pc_render_add_request;
 		ring->flush = gen4_render_ring_flush;
@@ -2113,24 +2113,27 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 			ring->dispatch_execbuffer =
 				gen6_ring_dispatch_execbuffer;
 		}
-		ring->semaphore.sync_to = gen6_ring_sync;
-		ring->semaphore.signal = gen6_signal;
-		/*
-		 * The current semaphore is only applied on pre-gen8 platform.
-		 * And there is no VCS2 ring on the pre-gen8 platform. So the
-		 * semaphore between VCS and VCS2 is initialized as INVALID.
-		 * Gen8 will initialize the sema between VCS2 and VCS later.
-		 */
-		ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_VR;
-		ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_INVALID;
-		ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_VB;
-		ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_VVE;
-		ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
-		ring->semaphore.mbox.signal[RCS] = GEN6_RVSYNC;
-		ring->semaphore.mbox.signal[VCS] = GEN6_NOSYNC;
-		ring->semaphore.mbox.signal[BCS] = GEN6_BVSYNC;
-		ring->semaphore.mbox.signal[VECS] = GEN6_VEVSYNC;
-		ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+		if (i915_semaphore_is_enabled(dev)) {
+			ring->semaphore.sync_to = gen6_ring_sync;
+			ring->semaphore.signal = gen6_signal;
+			/*
+			 * The current semaphore is only applied on pre-gen8
+			 * platform.  And there is no VCS2 ring on the pre-gen8
+			 * platform. So the semaphore between VCS and VCS2 is
+			 * initialized as INVALID.  Gen8 will initialize the
+			 * sema between VCS2 and VCS later.
+			 */
+			ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_VR;
+			ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_INVALID;
+			ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_VB;
+			ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_VVE;
+			ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
+			ring->semaphore.mbox.signal[RCS] = GEN6_RVSYNC;
+			ring->semaphore.mbox.signal[VCS] = GEN6_NOSYNC;
+			ring->semaphore.mbox.signal[BCS] = GEN6_BVSYNC;
+			ring->semaphore.mbox.signal[VECS] = GEN6_VEVSYNC;
+			ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+		}
 	} else {
 		ring->mmio_base = BSD_RING_BASE;
 		ring->flush = bsd_ring_flush;
@@ -2231,24 +2234,26 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
 		ring->irq_put = gen6_ring_put_irq;
 		ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
 	}
-	ring->semaphore.sync_to = gen6_ring_sync;
-	ring->semaphore.signal = gen6_signal;
-	/*
-	 * The current semaphore is only applied on pre-gen8 platform. And
-	 * there is no VCS2 ring on the pre-gen8 platform. So the semaphore
-	 * between BCS and VCS2 is initialized as INVALID.
-	 * Gen8 will initialize the sema between BCS and VCS2 later.
-	 */
-	ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_BR;
-	ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_BV;
-	ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_INVALID;
-	ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_BVE;
-	ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
-	ring->semaphore.mbox.signal[RCS] = GEN6_RBSYNC;
-	ring->semaphore.mbox.signal[VCS] = GEN6_VBSYNC;
-	ring->semaphore.mbox.signal[BCS] = GEN6_NOSYNC;
-	ring->semaphore.mbox.signal[VECS] = GEN6_VEBSYNC;
-	ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+	if (i915_semaphore_is_enabled(dev)) {
+		ring->semaphore.signal = gen6_signal;
+		ring->semaphore.sync_to = gen6_ring_sync;
+		/*
+		 * The current semaphore is only applied on pre-gen8 platform.
+		 * And there is no VCS2 ring on the pre-gen8 platform. So the
+		 * semaphore between BCS and VCS2 is initialized as INVALID.
+		 * Gen8 will initialize the sema between BCS and VCS2 later.
+		 */
+		ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_BR;
+		ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_BV;
+		ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_INVALID;
+		ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_BVE;
+		ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
+		ring->semaphore.mbox.signal[RCS] = GEN6_RBSYNC;
+		ring->semaphore.mbox.signal[VCS] = GEN6_VBSYNC;
+		ring->semaphore.mbox.signal[BCS] = GEN6_NOSYNC;
+		ring->semaphore.mbox.signal[VECS] = GEN6_VEBSYNC;
+		ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+	}
 	ring->init = init_ring_common;
 
 	return intel_init_ring_buffer(dev, ring);
@@ -2281,18 +2286,20 @@ int intel_init_vebox_ring_buffer(struct drm_device *dev)
 		ring->irq_put = hsw_vebox_put_irq;
 		ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
 	}
-	ring->semaphore.sync_to = gen6_ring_sync;
-	ring->semaphore.signal = gen6_signal;
-	ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_VER;
-	ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_VEV;
-	ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_VEB;
-	ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_INVALID;
-	ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
-	ring->semaphore.mbox.signal[RCS] = GEN6_RVESYNC;
-	ring->semaphore.mbox.signal[VCS] = GEN6_VVESYNC;
-	ring->semaphore.mbox.signal[BCS] = GEN6_BVESYNC;
-	ring->semaphore.mbox.signal[VECS] = GEN6_NOSYNC;
-	ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+	if (i915_semaphore_is_enabled(dev)) {
+		ring->semaphore.sync_to = gen6_ring_sync;
+		ring->semaphore.signal = gen6_signal;
+		ring->semaphore.mbox.wait[RCS] = MI_SEMAPHORE_SYNC_VER;
+		ring->semaphore.mbox.wait[VCS] = MI_SEMAPHORE_SYNC_VEV;
+		ring->semaphore.mbox.wait[BCS] = MI_SEMAPHORE_SYNC_VEB;
+		ring->semaphore.mbox.wait[VECS] = MI_SEMAPHORE_SYNC_INVALID;
+		ring->semaphore.mbox.wait[VCS2] = MI_SEMAPHORE_SYNC_INVALID;
+		ring->semaphore.mbox.signal[RCS] = GEN6_RVESYNC;
+		ring->semaphore.mbox.signal[VCS] = GEN6_VVESYNC;
+		ring->semaphore.mbox.signal[BCS] = GEN6_BVESYNC;
+		ring->semaphore.mbox.signal[VECS] = GEN6_NOSYNC;
+		ring->semaphore.mbox.signal[VCS2] = GEN6_NOSYNC;
+	}
 	ring->init = init_ring_common;
 
 	return intel_init_ring_buffer(dev, ring);
