[xmonad] How to manage three monitors on two graphics cards?

Mike Meyer mwm at mired.org
Sun Jan 8 02:44:12 CET 2012

On Fri, 6 Jan 2012 23:18:50 -0500
Wolfram Kahl <kahl at cas.mcmaster.ca> wrote:

> On Fri, Jan 06, 2012 at 08:10:48AM -0800, Mike Meyer wrote:
> > On Thu, 5 Jan 2012 20:31:59 -0500
> > Wolfram Kahl <kahl at cas.mcmaster.ca> wrote:
> > > On Thu, Jan 05, 2012 at 05:08:29PM -0800, Mike Meyer wrote:
> > > > Xrandr is the preferred solution. Xinerama has missing functionality
> > > > and vague specs.
> > > 
> > > However:
> > > 
> > >  * With Xinerama on, xrandr is not available.
> > 
> > That doesn't seem right.  Both systems I have available have both the
> > xrandr and xinerama extensions working in the X server. At least, I
> > can query the screen info using either extension. What makes you say
> > this?
> The fact that while I am running an X server with Xinerama On,
> when I issue the command ``xrandr'', I only get the error message:
> RandR extension missing

That may be a sign that something else is wonky. Like:

> On Thu, Jan 05, 2012 at 11:20:40PM -0400, Norbert Zeh wrote:
> Unfortunately, my current impression is that the radeon driver might be
> the source of at least the differences, and probably even of the problems...

I did find one note about that - seemed to indicated that xrandr
wouldn't support multiple cards, and the current radeon driver
expected you to use xrandr and didn't support xinerama properly. It
was a couple of years old (using the beta xrandr 1.3 code), though.

> > # 1) Specify the relative screen positioning in the ServerLayout section
> (absolute)
> > # 2) Have one Device section per monitor.  That is, the card with two monitors
> > # has two corresponding Device sections with different Screen numbers.
> > # According to man xorg.conf, this is as it should be, and it certainly is the
> > # only way I ever got xinerama to work on any of my setups.
> I had not noticed that previously, but had only seen somewhere
> the version with the two DVI-* outputs specified to two monitors
> in a single device section.
> man xorg.conf is indeed quite unambiguous about that,
> but my radeon driver seems to not like those Screen lines at all:
>  (EE) RADEON(1):  reusing fd for second head
> I tried setting Screen 2 on AsusV1, but that gives:
>  (EE) Screen 2 deleted because of no matching config section.
> Re-inserting the
>   Option "Monitor-DVI-*" XYZ
> lines AND removing the Screen lines was the only way
> I got to a point where a terminal would start.
> On Fri, Jan 06, 2012 at 08:10:48AM -0800, Mike Meyer also wrote:
> > > I wanted to say, more precisely, that I consider the output of
> > > Graphics.X11.Xinerama.getScreenInfo to be either wrong,
> > > or inappropriate for xmonad to base its screen subdivisions on.
> > 
> > Ah, right. yeah, the ghc output is wrong.
> > 
> > The solution seems to be to list the two outputs on the one card as
> > different devices, at least according to this:
> > 
> > https://bbs.archlinux.org/viewtopic.php?id=115596
> That essentially just gave me the additional hint to try ZaphodHeads:
> The only difference is that it starts with a wide Viewport on Apple1 and Samsung1,
> with Samsung1 still fixed in the upper left corner and Apple1 still panning,
> and the mouse still doesn't reach AsusV1.
>   http://sqrl.mcmaster.ca/~kahl/Xorg.0.log_H
>   http://sqrl.mcmaster.ca/~kahl/xorg.conf_H

I'm getting a "webpage not accessible" error trying to read these.

But you've got Xinerama on, multiple Device sections, using
ZaphodHeads to select the output on the card with two monitors? That
seems to be the key to this guys setup.

Just out of curiosity, have you tried a different window manager? Say
the default one, to see if you get the screens sorted properly? Or did
I already ask that (I know I meant to)?

Mike Meyer <mwm at mired.org>		http://www.mired.org/
Independent Software developer/SCM consultant, email for more information.

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