diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 04bdc7a91d53..7e51dd40bf6e 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -457,6 +457,19 @@ Userspace API Structures
 .. kernel-doc:: include/uapi/drm/drm_mode.h
    :doc: overview
 
+.. _crtc_index:
+
+CRTC index
+----------
+
+CRTC's have both an object ID and an index, and they are not the same thing.
+The index is used in cases where a densely packed identifier for a CRTC is
+needed, for instance a bitmask of CRTC's. The member possible_crtcs of struct
+drm_mode_get_plane is an example.
+
+DRM_IOCTL_MODE_GETRESOURCES populates a structure with an array of CRTC ID's,
+and the CRTC index is its position in this array.
+
 .. kernel-doc:: include/uapi/drm/drm.h
    :internal:
 
diff --git a/drivers/gpu/drm/drm_debugfs_crc.c b/drivers/gpu/drm/drm_debugfs_crc.c
index 3dd70d813f69..bbc3bc4ba844 100644
--- a/drivers/gpu/drm/drm_debugfs_crc.c
+++ b/drivers/gpu/drm/drm_debugfs_crc.c
@@ -46,10 +46,10 @@
  * it reached a given hardware component (a CRC sampling "source").
  *
  * Userspace can control generation of CRCs in a given CRTC by writing to the
- * file dri/0/crtc-N/crc/control in debugfs, with N being the index of the CRTC.
- * Accepted values are source names (which are driver-specific) and the "auto"
- * keyword, which will let the driver select a default source of frame CRCs
- * for this CRTC.
+ * file dri/0/crtc-N/crc/control in debugfs, with N being the :ref:`index of
+ * the CRTC<crtc_index>`. Accepted values are source names (which are
+ * driver-specific) and the "auto" keyword, which will let the driver select a
+ * default source of frame CRCs for this CRTC.
  *
  * Once frame CRC generation is enabled, userspace can capture them by reading
  * the dri/0/crtc-N/crc/data file. Each line in that file contains the frame
diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index d043752a74cf..e1f49dd241f7 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -635,8 +635,8 @@ struct drm_gem_open {
 /**
  * DRM_CAP_VBLANK_HIGH_CRTC
  *
- * If set to 1, the kernel supports specifying a CRTC index in the high bits of
- * &drm_wait_vblank_request.type.
+ * If set to 1, the kernel supports specifying a :ref:`CRTC index<crtc_index>`
+ * in the high bits of &drm_wait_vblank_request.type.
  *
  * Starting kernel version 2.6.39, this capability is always set to 1.
  */