[Openchrome-devel] [Bug 91966] No signal to monitor with X and openchrome using VX855 chipset graphics

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91966

--- Comment #202 from Kevin Brace <kevinbrace at gmx.com> ---
(In reply to HuangRan from comment #201)

Hi Frank,

> Hi Guys,
> 
>    Returning from my holiday and looking at this thread from the start to
> the end takes me several hours to do so although I have to skip some content
> for your chat becuase it is so long.
>    As I replied the mail to Kevin, I prefer to put my more time on
> OpenChrome and has several guys invovled on this project. So I hope I can
> provide some useful informaiton on this bug too.
>    So is this bug fixed or not? Does I2C 2 probe EDID information from DVI
> interface?
> 
> Thanks,
> Frank

The way the code works right now with the patch is that I2C bus 1 and 2 are
used for VGA related monitor detection.
xserver's API returns a structure that tells the caller if the monitor type is
analog or digital.
I use this information to see if I2C bus 1 or 2 is connected to an analog
monitor (i.e., VGA monitor).
I read the Intel DDX UMS code, and they apparently do this.
As for DVI, I2C bus 2 or 3 are used for communicating with the monitor and an
external TMDS transmitter chip.
In other words, I2C bus 2 can be used for VGA, DVI, or even a TV encoder chip.
The code that handles an external TMDS transmitter for DVI (i.e., VT1632A chip)
is still relatively unproven.
It was donated in early 2015, but there was a bug in it, and I help fix it with
the person who reported it (Bug 93675).
I do own about 10 or so VIA Technologies IGP based mainboards / computers at my
place, but I do not really have a functional mainboard / computer with DVI
coming out of it at this point that is not a thin client.

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