drm/i915: Mask USER interrupts on gen6 (until required)

Otherwise we may consume 20% of the CPU just handling IRQs whilst
rendering. Ouch.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 5969c2e..634f6f8 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -28,6 +28,8 @@
 #define I915_READ_CTL(ring) I915_RING_READ(RING_CTL(ring->mmio_base))
 #define I915_WRITE_CTL(ring, val) I915_WRITE(RING_CTL(ring->mmio_base), val)
 
+#define I915_WRITE_IMR(ring, val) I915_WRITE(RING_IMR(ring->mmio_base), val)
+
 #define I915_READ_NOPID(ring) I915_RING_READ(RING_NOPID(ring->mmio_base))
 #define I915_READ_SYNC_0(ring) I915_RING_READ(RING_SYNC_0(ring->mmio_base))
 #define I915_READ_SYNC_1(ring) I915_RING_READ(RING_SYNC_1(ring->mmio_base))
@@ -52,6 +54,7 @@
 	int		effective_size;
 	struct intel_hw_status_page status_page;
 
+	u32		irq_mask;
 	u32		irq_seqno;		/* last seq seem at irq time */
 	u32		waiting_seqno;
 	u32		sync_seqno[I915_NUM_RINGS-1];