Multiseat with VGAArbiter on 2 Radeon cards - found KMS

Steven J Newbury steve at
Tue Dec 22 14:00:13 PST 2009

On Tue, 2009-12-22 at 17:49 +0000, Steffen Schaumburg wrote:
> Ok I just realised that KMS has to be activated in staging. So I tried
> that now, but without success :(
> So I tried 3 kernel configs now.
> In common they have:
> Kernel 2.6.32 (gentoo-sources)
> xorg-server 1.7.3
> using the xorg radeon/ati driver
> identical xorg.conf and kdmrc (attached)
> Both boot in text mode fine
> The differences (all configs are attached):
> 1) had KMS and DRM off
> 2) DRM on
> 3) DRM and KMS on
> Now the results vary quite a bit.
> All of them start booting in textmode on the monitor connected to the
> primary graphics card.
> 1 and 2 continue to boot and allow me to do a text login. However with
> KMS on by default the monitor suddenly goes black (but not into standby)
> during boot, I think when it starts loading the modules but I'm not
> quite sure, it's hard to tell because the messages come so fast at that
> point. However I can still login blindly. If I try to start KDM nothing
> changes on the screens.
> As said 1 and 2 let me login normally so here's what happens from then:
> With the kernel without DRM I can start KDM and it displays on the
> screen connected to the secondary card (note: this is the first entry in
> kdmrc). I can then login and work on that monitor just fine, in fact I'm
> writing this email from it.
> With the kernel with DRM it's not so good. The second monitor turns on
> but both just go blank and stay blank.
> Note that in all of the scenarios I can always cause an orderly shutdown
> by pressing the power button.
> Any ideas?
> Thanks, Steffen
> > Okay I tried turning off arbiter by just editing .config
> > ("CONFIG_VGA_ARB=n") but when I type my usual "make && make
> > modules_install" it changes it back automatically. I tried rebooting
> > into this new kernel anyways but it continues to load arbiter as
> > evidenced in the boot messages and as expected it still doesn't work. I
> > haven't been able to turn off arbiter in make menuconfig as its
> > automatically turned on by other options so it doesn't even show up in
> > there.
You don't want to turn it off.  It is needed to cleanly boot with two
VGA cards.

> >
> > Does anyone have any ideas what I'm doing? Or is anyone out here running
> > a multiseat setup with radeon cards? I'd be very very grateful if you
> > could send me your xorg.conf, ?dm config (e.g.
> > /usr/share/config/kdm/kdmrc), the version numbers of your xorg-server,
> > type&version of driver (at this stage I'd even try the proprietary
> > drivers) and what you use to launch X as well as its version.
> >
> > So any tips, no matter how unlikely you think they are to work, would be
> > greatly appreciated.
Given how you've mentioned DRM failing, have you checked it's
successfully loading the microcode for both cards?  DRM should be
working with multiple cards.

I have a dual Radeon system RV280 (PCI) + R420 (AGP), I too was having
some problems bringing it up successfully.  What I found is I had to go
with what the DRM driver determines to be the card order (PCI as
primary), not what the BIOS has set (AGP as primary).  It is apparently
essential to have the cards initialised in this order.

Until you get it working, you probably want to use -retro so you can
tell you've got the server running properly.

I haven't yet tried multi-seat, but have it working with multi-screen, I
had hoped to find some way of binding input devices to a single screen,
but the code isn't yet in place, so I'll be trying multi-seat again. (I
previously had it working with the old UMS drivers.)

I've attached the drm log from my boot with two working Radeons + KMS.

I won't be about for a couple of weeks so I won't be able to help
further until then.
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