1 files changed, 48 insertions, 0 deletions

diff --git a/Documentation/fb/viafb.txt b/Documentation/fb/viafb.txt
index f3e046a6a987..1a2e8aa3fbb1 100644
--- a/Documentation/fb/viafb.txt
+++ b/Documentation/fb/viafb.txt
@@ -197,6 +197,54 @@ Notes:
        example,
            # fbset -depth 16
 
+
+[Configure viafb via /proc]
+---------------------------
+    The following files exist in /proc/viafb
+
+    supported_output_devices
+
+        This read-only file contains a full ',' seperated list containing all
+        output devices that could be available on your platform. It is likely
+        that not all of those have a connector on your hardware but it should
+        provide a good starting point to figure out which of those names match
+        a real connector.
+        Example:
+        # cat /proc/viafb/supported_output_devices
+
+    iga1/output_devices
+    iga2/output_devices
+
+        These two files are readable and writable. iga1 and iga2 are the two
+        independent units that produce the screen image. Those images can be
+        forwarded to one or more output devices. Reading those files is a way
+        to query which output devices are currently used by an iga.
+        Example:
+        # cat /proc/viafb/iga1/output_devices
+        If there are no output devices printed the output of this iga is lost.
+        This can happen for example if only one (the other) iga is used.
+        Writing to these files allows adjusting the output devices during
+        runtime. One can add new devices, remove existing ones or switch
+        between igas. Essentially you can write a ',' seperated list of device
+        names (or a single one) in the same format as the output to those
+        files. You can add a '+' or '-' as a prefix allowing simple addition
+        and removal of devices. So a prefix '+' adds the devices from your list
+        to the already existing ones, '-' removes the listed devices from the
+        existing ones and if no prefix is given it replaces all existing ones
+        with the listed ones. If you remove devices they are expected to turn
+        off. If you add devices that are already part of the other iga they are
+        removed there and added to the new one.
+        Examples:
+        Add CRT as output device to iga1
+        # echo +CRT > /proc/viafb/iga1/output_devices
+
+        Remove (turn off) DVP1 and LVDS1 as output devices of iga2
+        # echo -DVP1,LVDS1 > /proc/viafb/iga2/output_devices
+
+        Replace all iga1 output devices by CRT
+        # echo CRT > /proc/viafb/iga1/output_devices
+
+
 [Bootup with viafb]:
 --------------------
     Add the following line to your grub.conf: