1 files changed, 5 insertions, 0 deletions

diff --git a/Documentation/fb/udlfb.txt b/Documentation/fb/udlfb.txt
index 7fdde2a02a27..473ceed9e4eb 100644
--- a/Documentation/fb/udlfb.txt
+++ b/Documentation/fb/udlfb.txt
@@ -105,6 +105,11 @@ console		Allow fbcon to attach to udlfb provided framebuffers. This
                 the first framebuffer it finds, which isn't usually what the
                 user wants in the case of USB displays.
 
+shadow          Allocate a 2nd framebuffer to shadow what's currently across
+                the USB bus in device memory. If any pixels are unchanged,
+                do not transmit. Spends host memory to save USB transfers.
+                Enabled by default. Only disable on very low memory systems.
+
 Sysfs Attributes
 ================