drm/i915: Add new GET_PIPE_FROM_CRTC_ID ioctl.

This allows userlevel code to discover the pipe number corresponding
to a given CRTC ID. This is necessary for doing pipe-specific
operations such as waiting for vblank on a given CRTC.  Failure to use
the right pipe mapping can result in GPU hangs, or at least failure
to actually sync to vblank.

Signed-off-by: Carl Worth <cworth@cworth.org>
[anholt: Style touchups from review]
Signed-off-by: Eric Anholt <eric@anholt.net>
diff --git a/include/drm/i915_drm.h b/include/drm/i915_drm.h
index 95962fa..8e1e925 100644
--- a/include/drm/i915_drm.h
+++ b/include/drm/i915_drm.h
@@ -184,6 +184,7 @@
 #define DRM_I915_GEM_GET_TILING	0x22
 #define DRM_I915_GEM_GET_APERTURE 0x23
 #define DRM_I915_GEM_MMAP_GTT	0x24
+#define DRM_I915_GET_PIPE_FROM_CRTC_ID	0x25
 
 #define DRM_IOCTL_I915_INIT		DRM_IOW( DRM_COMMAND_BASE + DRM_I915_INIT, drm_i915_init_t)
 #define DRM_IOCTL_I915_FLUSH		DRM_IO ( DRM_COMMAND_BASE + DRM_I915_FLUSH)
@@ -219,6 +220,7 @@
 #define DRM_IOCTL_I915_GEM_SET_TILING	DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_SET_TILING, struct drm_i915_gem_set_tiling)
 #define DRM_IOCTL_I915_GEM_GET_TILING	DRM_IOWR (DRM_COMMAND_BASE + DRM_I915_GEM_GET_TILING, struct drm_i915_gem_get_tiling)
 #define DRM_IOCTL_I915_GEM_GET_APERTURE	DRM_IOR  (DRM_COMMAND_BASE + DRM_I915_GEM_GET_APERTURE, struct drm_i915_gem_get_aperture)
+#define DRM_IOCTL_I915_GET_PIPE_FROM_CRTC_ID DRM_IOWR(DRM_COMMAND_BASE + DRM_I915_GET_PIPE_FROM_CRTC_ID, struct drm_intel_get_pipe_from_crtc_id)
 
 /* Allow drivers to submit batchbuffers directly to hardware, relying
  * on the security mechanisms provided by hardware.
@@ -657,4 +659,12 @@
 	__u64 aper_available_size;
 };
 
+struct drm_i915_get_pipe_from_crtc_id {
+	/** ID of CRTC being requested **/
+	__u32 crtc_id;
+
+	/** pipe of requested CRTC **/
+	__u32 pipe;
+};
+
 #endif				/* _I915_DRM_H_ */