[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 #113 from Kevin Brace <kevinbrace at gmx.com> ---
(In reply to Christopher from comment #112)

Hi Christopher,

> I'm looking forward to what you come up with :)
> 
> May I ask what happens at the beginning of February? Just curious. Promise :)

Yeah, I have been doing some experiments on how the current code base of
OpenChrome can wean off using a predefined table for display outputs (i.e., the
two patches Xavier uploaded for you to test).
After several days of frustrating debugging work, at least for my own VIA
Technologies silicon-based laptop (Epic 1314 laptop - MSI VR321 laptop
equivalent), I can now boot Lubuntu 12.04 without the use of a display output
predefined table.
OpenChrome correctly detects an LVDS-based DFP (i.e., laptop LCD screen) and an
external VGA monitor, and automatically configure them.
Basically, I had to struggle for several days on this issue because a large
patch written by Christian Jung had a likely bug that will cause a segmentation
fault when ran on devices "without" VT1632A TMDS transmitter (This external
small chip is to provide DVI functionality for devices without an integrated
TMDS transmitter like VN896 chipset.).

http://cgit.freedesktop.org/openchrome/xf86-video-openchrome/commit/?id=a8c2f04e2ef21e64f2e91dd6f3e237f80e8c80c6

Please note that I am not blaming anyone for the likely bug.
This large patch was accepted in early January 2015 (almost 1 year ago), but
due to the way it was written, it only ran if P4M800 Pro or closely related
chipset (i.e., CN700 chipset) was running OpenChrome.
The reality is, VT1632A can be hooked up to devices other than P4M800 Pro
chipset, and in fact, I do own a dead VN896 chipset industrial computer with
VT1632A attached to it for DVI output (I had to write this one off since it
died so quickly after I purchased off ebay.)
Again, I am trying to make the code more robust by basically doing automatic
detection for pretty much all known VIA Technologies external transmitter /
encoder devices.
I hate to say this, but I think this will likely break some people's
Linux-based computers with VIA Technologies integrated graphics since the
predefined table probably prevents some computers from freezing during boot
time.
My view is that this is not nice, but I feel like this project has to cross
this bridge of relying less and less on a predefined table at some point, and I
feel like this is a good time to go over the hump.
This will mean that people who still own VIA Technologies-based computers
hopefully can do testing of the newer OpenChrome code base, and let the
developers know (I guess I am practically the only one left at this point.) the
results.
For the next few weeks, I only have access to this laptop I am writing this
message.
I will like to see the stability of OpenChrome code improve substantially to
Intel SandyBridge or later integrated graphics level device driver someday, but
I suppose this will take many, many years to get there.
    So why is what I am working on currently relevant to your situation?
It is relevant because I strongly suspect that the issue you are facing is
related to display output detection, based on the error messages I have
analyzed.
In your case, you have VX855 chipset, so in some ways, the situation is better.
VX855 chipset has an integrated TMDS transmitter for DVI output, and hardware
programming documentation is readily available unlike other chipsets like VN896
chipset.
I have soon look into how the integrated DFP (Digital Flat Panel) transmitters
(i.e., LVDS and TMDS) are handled in OpenChrome for CX700, VX800, VX855, and
VX900 chipsets, and see if I can come up with something for you to try.
Of course, I will get a patch ready at that point.
I cannot promise when this will be ready, so hopefully I will have something to
show for in the next few weeks.

Regards,

Kevin Brace

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