How to report DVI/HDMI support to Xrandr?

Matthias Hopf mhopf at
Mon Mar 10 06:20:55 PDT 2008

On Mar 07, 08 12:03:18 -0500, Endejan, Edward wrote:
> 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

I started this discussion, and I'm glad that finally someone is
commenting on it :)
Though I think it would work. In my notion RANDR_SIGNAL_FORMAT would be
non-static, so the driver could change this to TMDS-DVI or TMDS-HDMI
accordingly. AFAICS there *are* some differences in the signal, like
Audio being present, or maximum link bandwidth (TMDS-HDMI-13: 340MHz),
and 10/12/16 bit xvYCC video.

Do you think this would suffice?

> 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?

Hm. Sounds reasonable.

> 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

It does work for the radeonhd driver in my environment, so in principle
the mechanisms work.


Matthias Hopf <mhopf at>      __        __   __
Maxfeldstr. 5 / 90409 Nuernberg   (_   | |  (_   |__          mat at
Phone +49-911-74053-715           __)  |_|  __)  |__  R & D

More information about the xorg mailing list