diff --git a/include/hardware/hwcomposer.h b/include/hardware/hwcomposer.h
index 27b9197..a6358e4 100644
--- a/include/hardware/hwcomposer.h
+++ b/include/hardware/hwcomposer.h
@@ -342,8 +342,16 @@
      * handles have been updated. Typically this happens (but is not limited to)
      * when a window is added, removed, resized or moved.
      *
-     * The numDisplays parameter will always be greater than zero, displays
-     * will be non-NULL, and the array entries will be non-NULL.
+     * For HWC 1.0, numDisplays will always be one, and displays[0] will be
+     * non-NULL.
+     *
+     * For HWC 1.1, numDisplays will always be HWC_NUM_DISPLAY_TYPES. Entries
+     * for unsupported or disabled/disconnected display types will be NULL.
+     *
+     * For HWC 1.2 and later, numDisplays will be HWC_NUM_DISPLAY_TYPES or more.
+     * The extra entries correspond to enabled virtual displays, and will be
+     * non-NULL. In HWC 1.2, support for one virtual display is required, and
+     * no more than one will be used. Future HWC versions might require more.
      *
      * returns: 0 on success. An negative error code on error. If an error is
      * returned, SurfaceFlinger will assume that none of the layer will be
@@ -368,8 +376,16 @@
      * been handled by SurfaceFlinger with OpenGL ES. In this case, (*set)()
      * behaves just like eglSwapBuffers().
      *
-     * The numDisplays parameter will always be greater than zero, displays
-     * will be non-NULL, and the array entries will be non-NULL.
+     * For HWC 1.0, numDisplays will always be one, and displays[0] will be
+     * non-NULL.
+     *
+     * For HWC 1.1, numDisplays will always be HWC_NUM_DISPLAY_TYPES. Entries
+     * for unsupported or disabled/disconnected display types will be NULL.
+     *
+     * For HWC 1.2 and later, numDisplays will be HWC_NUM_DISPLAY_TYPES or more.
+     * The extra entries correspond to enabled virtual displays, and will be
+     * non-NULL. In HWC 1.2, support for one virtual display is required, and
+     * no more than one will be used. Future HWC versions might require more.
      *
      * IMPORTANT NOTE: there is an implicit layer containing opaque black
      * pixels behind all the layers in the list. It is the responsibility of
diff --git a/include/hardware/hwcomposer_defs.h b/include/hardware/hwcomposer_defs.h
index a5df8f0..f0f97fc 100644
--- a/include/hardware/hwcomposer_defs.h
+++ b/include/hardware/hwcomposer_defs.h
@@ -139,6 +139,12 @@
      * returns the vsync period in nanosecond
      */
     HWC_VSYNC_PERIOD                    = 1,
+
+    /*
+     * availability: HWC_DEVICE_API_VERSION_1_1
+     * returns a mask of supported display types
+     */
+    HWC_DISPLAY_TYPES_SUPPORTED         = 2,
 };
 
 /* Allowed events for hwc_methods::eventControl() */
@@ -146,6 +152,18 @@
     HWC_EVENT_VSYNC     = 0
 };
 
+/* Display types and associated mask bits. */
+enum {
+    HWC_DISPLAY_PRIMARY     = 0,
+    HWC_DISPLAY_EXTERNAL    = 1,    // HDMI, DP, etc.
+    HWC_NUM_DISPLAY_TYPES
+};
+
+enum {
+    HWC_DISPLAY_PRIMARY_BIT     = 1 << HWC_DISPLAY_PRIMARY,
+    HWC_DISPLAY_EXTERNAL_BIT    = 1 << HWC_DISPLAY_EXTERNAL,
+};
+
 /*****************************************************************************/
 
 __END_DECLS