A lot of devices do not need and do not document port or endpoint
numbering at all, e.g. in case where there's just a single port and a
single endpoint. Whereas this is just common sense, document it to make it
explicit.

Signed-off-by: Sakari Ailus <sakari.ai...@linux.intel.com>
---
 Documentation/devicetree/bindings/media/video-interfaces.txt | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt 
b/Documentation/devicetree/bindings/media/video-interfaces.txt
index 852041a..4e0527d 100644
--- a/Documentation/devicetree/bindings/media/video-interfaces.txt
+++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
@@ -55,6 +55,18 @@ divided into two separate ITU-R BT.656 8-bit busses.  In 
such case bus-width
 and data-shift properties can be used to assign physical data lines to each
 endpoint node (logical bus).
 
+Port and endpoint numbering
+---------------------------
+
+While the port and endpoint numbers are ultimately specific to a device,
+most devices have more limited scope than what the interface allows. They
+may, for instance, only support a single endpoint on a port. Or there may
+be only a single port on a device.
+
+Therefore, if ports are not explicitly documented for a device, only port
+number zero shall be used. The same applies to endpoints: if endpoint
+numbers are not explicitly documented, only endpoint number zero shall be
+used.
 
 Required properties
 -------------------
-- 
2.7.4

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