@@ -1161,6 +1161,12 @@ int max_width, max_height;</synopsis>
any new rendering to the frame buffer until the page flip completes.
</para>
<para>
+ If a page flip can be successfully scheduled the driver must set the
+ <code>drm_crtc-<fb</code> field to the new framebuffer pointed to
+ by <code>fb</code>. This is important so that the reference counting
+ on framebuffers stays balanced.
+ </para>
+ <para>
If a page flip is already pending, the
<methodname>page_flip</methodname> operation must return
-<errorname>EBUSY</errorname>.
@@ -3792,6 +3792,13 @@ int drm_mode_page_flip_ioctl(struct drm_device *dev,
/* Keep the old fb, don't unref it. */
old_fb = NULL;
} else {
+ /*
+ * Warn if the driver hasn't properly updated the crtc->fb
+ * field to reflect that the new framebuffer is now used.
+ * Failing to do so will screw with the reference counting
+ * on framebuffers.
+ */
+ WARN_ON(crtc->fb != fb);
/* Unref only the old framebuffer. */
fb = NULL;
}