diff --git a/include/hardware/gralloc.h b/include/hardware/gralloc.h
index dba6fda..d88591f 100644
--- a/include/hardware/gralloc.h
+++ b/include/hardware/gralloc.h
@@ -244,8 +244,22 @@
             int interval);
 
     /*
-     * sets a rectangle evaluated during (*post)() specifying which area
-     * of the buffer passed in (*post)() needs to be posted.
+     * This hook is OPTIONAL.
+     * 
+     * It is non NULL If the framebuffer driver supports "update-on-demand" 
+     * and the given rectangle is the area of the screen that gets 
+     * updated during (*post)().
+     * 
+     * This is useful on devices that are able to DMA only a portion of
+     * the screen to the display panel, upon demand -- as opposed to
+     * constantly refreshing the panel 60 times per second, for instance.
+     * 
+     * Only the area defined by this rectangle is guranteed to be valid, that
+     * is, the driver is not allowed to post anything outside of this
+     * rectangle. 
+     * 
+     * The rectangle evaluated during (*post)() and specifies which area
+     * of the buffer passed in (*post)() shall to be posted.
      * 
      * return -EINVAL if width or height <=0, or if left or top < 0 
      */
diff --git a/modules/gralloc/framebuffer.cpp b/modules/gralloc/framebuffer.cpp
index 5077a0d..d885ae8 100644
--- a/modules/gralloc/framebuffer.cpp
+++ b/modules/gralloc/framebuffer.cpp
@@ -38,6 +38,9 @@
 
 /*****************************************************************************/
 
+// should be a build option
+#define SUPPORTS_UPDATE_ON_DEMAND   1
+
 #define NUM_BUFFERS 2
 
 
@@ -340,7 +343,9 @@
         dev->device.common.module = const_cast<hw_module_t*>(module);
         dev->device.common.close = fb_close;
         dev->device.setSwapInterval = fb_setSwapInterval;
+#if SUPPORTS_UPDATE_ON_DEMAND
         dev->device.setUpdateRect   = fb_setUpdateRect;
+#endif
         dev->device.post            = fb_post;
 
         private_module_t* m = (private_module_t*)module;