drm: i915: Add ioctl for scheduling buffer swaps at vertical blanks.

This uses the core facility to schedule a driver callback that will be called
ASAP after the given vertical blank interrupt with the HW lock held.

Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/char/drm/i915_dma.c b/drivers/char/drm/i915_dma.c
index fb7913f..9354ce3 100644
--- a/drivers/char/drm/i915_dma.c
+++ b/drivers/char/drm/i915_dma.c
@@ -162,6 +162,7 @@
 
 	dev_priv->ring.virtual_start = dev_priv->ring.map.handle;
 
+	dev_priv->cpp = init->cpp;
 	dev_priv->back_offset = init->back_offset;
 	dev_priv->front_offset = init->front_offset;
 	dev_priv->current_page = 0;
@@ -782,6 +783,7 @@
 	[DRM_IOCTL_NR(DRM_I915_DESTROY_HEAP)] = { i915_mem_destroy_heap, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY },
 	[DRM_IOCTL_NR(DRM_I915_SET_VBLANK_PIPE)] = { i915_vblank_pipe_set, DRM_AUTH|DRM_MASTER|DRM_ROOT_ONLY },
 	[DRM_IOCTL_NR(DRM_I915_GET_VBLANK_PIPE)] = { i915_vblank_pipe_get, DRM_AUTH },
+	[DRM_IOCTL_NR(DRM_I915_VBLANK_SWAP)] = {i915_vblank_swap, DRM_AUTH},
 };
 
 int i915_max_ioctl = DRM_ARRAY_SIZE(i915_ioctls);