Dual link on X1250 radeonhd git head fails

Adam J. Richter adam at yggdrasil.com
Wed Mar 26 22:46:40 PDT 2008

On Thu, Mar 20, 2008 at 10:05:39AM -0400, Alex Deucher wrote:
> On Thu, Mar 20, 2008 at 2:51 AM, Adam J. Richter <adam at yggdrasil.com> wrote:
> > On Mon, Mar 17, 2008 at 02:42:40PM +0100, Matthias Hopf wrote:
> >  > Current git of radeonhd should support dual link DVI as well, though
> >  > this is untested ATM.
> >
> >         I just tried the radeonhd git head (pulled minutes ago) on a
> >  30 inch 2560x1600 HP lp3065 monitor, and the screen is black with the
> >  green LED flashing.  This same screen displays BIOS messages, lilo
> >  text and the character mode linux console fine, as I think there is
> >  some built in video stretching done in character mode (for example, in
> >  character mode, my 1920x1200 monitor always claims to be receiving a
> >  1920x1200 signal rather than 640x480 or something similar that one
> >  would normally associate with character mode).  xrandr, correctly
> >  describes the video modes for my 1920x1200 monitor on the VGA cable
> >  and the 2560x1600 monitor on VGA, and indicates that 2560x1600 is
> >  selected, and the virtual screen size is expanded to 2560x1600.  So, I
> >  think this is a mode setting issue and not some misconfiguration on my
> >  part.
> >
> >         My new lp3065 can select between three dual-link DVI input
> >  cables, so I should be able to plug it into an nvidia card for now to
> >  use it immediately while still being available to test new changes
> >  through a cable connect to my AMD motherboard.  So, if anyone wants me
> >  to try a patch and report results, I am happy to do so when I have time.
> >
> >         Also, if anyone would like to point me to the relevant page
> >  numbers of the recently released X docs for the rs690 in
> >  http://www.x.org/docs/AMD/ for enabling dual link, I may be able to
> >  try to work on this myself during the weekend.  I had previously
> >  skimmed AMD's recently released documents but didn't immediately find
> >  a bit to set to activate dual link.
> Have you tried radeon?

	Yes.  With either radeon or radeonhd drivers, xrandr correctly
notes that 2560x1600 video mode is available, and that mode can be
selected with xrandr, but the video does not display correctly.  The
way the video is incorrect differs between radeonhd and radeon.  With
radeonhd, the screen displays a slowly changing rectangular pattern.
With radeon, the LED in the corner of the monitor changes from green
to orange and the screen is black.

	The above statements are true for the git versions of radeon
and readeonhd both as of a couple of days ago and as of git pulls from
about an hour ago.

>Also, your board may not support dual-link.

	It is possible that the DVI connector built into my Gigabyte
ma69gm-s2h motherboard is not dual link, although the am690g chipset
that this board uses is supposed to support dual link (the chipset
include the ATI X1250).  I have not yet found an example on the net of
anyone actually using this motherboard to drive a 2560x1600 monitor,
although a possibly mistaken review at
mentions in passing that the motherboard include "a dual-link DVI
port, which supports resolutions up to 2,560x1,600".

	Before answering your email, I attempted to install Microsoft
Windows Vista Professional, but another disk with this motherboard,
but, so far, I have been unable to get Windows Vista to driver this
video output with anything other than the "standard VGA" device
driver, even though I run Windows install program from the motherboard
manufacturer's driver page for this board.

	At least I can confirm for you that all three video inputs of
the monitor and both video cables that I use with this monitor work in
dual link, because I am able to run it at 2560x1600 with an EVGA
nVidia GeForce 8500 with the free xf86-video-nv-2.1.8 driver by
commenting out the lines in xf86-video-nv-2.1.8/src/g80_sor.c near the
remark "Disable dual-link modes until I can find a way to make them
work."  I have also made the the card and monitor work at 2560x1600
under MS-Windows Vista Pro.

	I am still looking into your question about whether this
motherboard might actually lack dual-link support, and plan to forward
the information to this list once I can confirm it one way or the
other, both for the benefit of driver devlopment and anyone
considering buying this model of motherboard.

	Thanks for your advice on this.

Adam Richter

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