[Openchrome-devel] [Bug 95059] DVI port failure with external TMDS transimitter for T510/T5555/C90LE thin clients

bugzilla-daemon at freedesktop.org bugzilla-daemon at freedesktop.org
Sat May 28 08:31:06 UTC 2016


--- Comment #8 from Kevin Brace <kevinbrace at gmx.com> ---
(In reply to frank from comment #6)

Hi Frank,

> Created attachment 124119 [details]
> Xorg.0.log of V90LE with UMS 0.4.0
> hi,I tried ums0.4.0 in V90LE with DVI port,it can't work,from the
> Xorg.0.log,it seems dvi port can't get the edid data correctly,and I found
> that in the source code of ddx,the dvi init function has been commented
> out(ViaOutputsDetect function in via_outputs.c),so I tried to uncomment
> it,then the edid can be read as in the attachments,but the display still
> can't work,so my question is that why comment out the via_dvi_init
> function,and this function seems just point at vt1632a transmiter,so if the
> board has no vt1632,how to init the dvi port?
> hope to get the answer.

Okay, here is the promised technical explanation of what is going on.
Previously, the OpenChrome developers used a thing called "known device table"
to decide which display output devices (i.e., VGA, DVI, TV, LVDS flat panel,
etc.) to initialize and activate during initialization.
As far as I am concerned, this is not the right way to do things anymore, and I
completely removed this table for Version 0.4.0.
The development resources are now directed towards automatic detection of
display output devices, and I have been doing some research on how to
accomplish this.
VIA IGPs do have a thing called pin strappings that can provide "hints" to the
graphics device driver regarding what kind of a transmitter / encoder is
connected to the IGP.
Furthermore, VIA IGPs do have some hardware level display presence detection
hardware integrated with the IGP to help perform display output device presence
    It sounds like an excuse, but I have been hampered by the lack of hardware
availability of devices with VT1632A TMDS transmitter.
I do own 2 function devices with VT1632A, but they are both thin client type
devices that are hard to do development work on them.
    If you can run the latest OpenChrome from the Git repository, that will be
helpful since I did add a functionality to read off the pin strapping recently.
This will help me figure out whether or not VT1632A is connected to DVP0
(sometimes called GDVP0) or DVP1.
DVP (Digital Video Port) is a connection to an external transmitter / encoder,
and depending on the configuration of the device, it can be a TV encoder or
TMDS transmitter.
I have written some lines of code to activate VT1632A on VX800, VX855, and
VX900 chipsets (code has not been committed to the Git repository yet), but
when I tested it with VX855 recently, DVI did not work.
I plan to revisit the code in the next few weeks when I "feel" like working on
this again.

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