setting up xorg.conf

Daniel Stone daniel at
Tue Apr 12 19:08:40 CDT 2005

On Tue, Apr 12, 2005 at 12:47:40PM -0500, Carl Karsten wrote:
> xorg guys have some interest in something that I thought I had seen here 
> but I can't find it.  Also, anyone leaning on ddcprobe may be interested 
> in what I found.
> google ddcprobe:

This is the source our ddcprobe is based off, yes.

> "ddcprobe 
> claims to do a "Videocard DDC probe". However, in the course of 
> troubleshooting bug 108681, I learned from Mike Harris that there is no 
> such thing.  I think it would be less misleading if it was called 
> something like a "Videocard VBE probe". Even if that's not the best 
> phrase either, it's much better and much closer to the truth than 
> "Videocard DDC probe".

'VBE probe' is rather meaningless -- what it should really say is 'VBE
DDC probe', but hopefully that won't be true for too long.  As that bug
says, DDC is a generic name for describing the sort of probe that gets
done.  VBE is one way to do it.  Doing it by setting up I2C channels and
poking them in specific ways is another way to do it.  We do the former.

> CarlK: it seems a common problem is getting the valid resolutions in 
> xorg.conf
> CarlK: valid = ones that will work with my hardware (video card, video 
> memory and monitor)
> ajax: if we had a way to probe DDC on a card without running all of X, 
			   he means via I2C channels
> we could do that pretty reliably
> ajax: linux might give you enough info through sysfs to make that possible
> CarlK: ever heard of ddcprobe?
> libv: CarlK: that most likely uses VESA

It sure does.

> CarlK:  /usr/sbin/ddcprobe - can't figure out where it comes from - no 
> man or info

Comes from the xresprobe package.

> libv: which makes it a BIOS dependant function, which only makes it 
> possible on the primary graphics card

Yeah, which sucks.

> ajax: probably the easy solution is to bump the default resolution to 
> 800x600,

No thanks.

> use DDC by default

Um, we already do.

> and cache the results of the DDC probe from the last server startup
> ajax: that last bit being important, so the monitor still works even if 
> you start X with it powered down.

Yeah, I've been meaning to get to that for a while.  Bug#5917.

> JakubS_: so there should be no problem with only primary card - from 
> what i have seen there is bios image for video card in /sys
> JakubS_: it would probably have to be run on emulator, like x server does

On i386, it runs natively.  On powerpc, it's exposed via /proc.  On
amd64, ia64, hppa and sparc, it doesn't run at all.  But eventually, it
will be run on an emulator (x86emu) like X does - Bug#1421.

> If someone can give me the subject(s) of the ubuntu threads (pretty sure 
> it was here) I'll forward it to xorg at

Which Ubuntu threads?
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