How to report DVI/HDMI support to Xrandr?

Endejan, Edward eendejan at
Fri Mar 7 09:03:18 PST 2008

The driver I'm working on is now able to distinguish between an attached
display with HDMI support versus one with only DVI support (no audio) by
reading and parsing the second 128 bytes of the display's EDID
(Extension Block 1). My question is how to best report this information
through Xrandr.

I've searched quite a bit through the archives and have found some
discussion about Output Properties being used to describe CONNECTOR_TYPE
= { ... HDMI, DVI-A, DVI-D, ...} or SIGNALLING_LEVEL = {... TMDS, LVDS,
...} but I don't think either of these work for this use case. Either
HDMI or DVI connector types can be converted to the other type through
an adapter or cable, so it seems that just describing the physical
connector type which is present is not enough. Both HDMI and DVI use
TMDS signaling, but HDMI can interleave audio data along with the video
data. I still think that an Output Property would be a good method to
report this information though, so I'm proposing to create a new Output
Property called HDMI_AUDIO which would be set to TRUE when that
functionality is supported. Are there any objections to this approach?
Is there a better way or has this already been implemented in a
different way?

A separate issue is that some output properties (e.g EDID) that I
believe have been set by the driver do not seem to be getting through to
the other side and are not displayed when I use the --properties or
--verbose options on the command line with xrandr. Is it possible that I
do not have all the necessary supporting libraries for this pathway to
be functional? I know that libXrandr-1.2.2, libX11-1.1.3, libXext-1.0.2,
and libxcb-1.0 are available. Are there others that I need as well?

Any thoughts or suggestions would be appreciated.


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