Help debugging kernel together with X

[Glen Barber]

Hi, Fernando

2009/5/26 Fernando Herrero Carrón <fhcarron at terra.es>:
> Hi list,
>
> I would like to ask for some help debugging the kernel.
>
> Here is the problem:
>
> I have a computer about five years old with an on-board graphics card
> (SiS 661). I am trying to install an ATI Radeon 128 on the AGP port.
> FreeBSD (FreeBSD 7.2-STABLE #10: Tue May 26 15:08:39 CEST 2009) is able
> to start DRM and AGP without trouble. However, whenever I start X (X.Org
> X Server 1.6.1; Release Date: 2009-4-14; Build Date: 11 May 2009
> 12:03:27PM) the system freezes with a blank screen with some apparent
> noisy green dots on it (reproducible, however). It does not panic, nor
> reboot.
>
> Now I suspect there is some problem on the AGP bridge driver since linux
> can run X without trouble (i.e. hardware and BIOS are ok). I have found
> someone reporting problems with this bridge long time ago with no
> answers (http://www.nabble.com/agp-on-sis-661-td1446998.html).
>
> So here I am trying to figure out where the system freezes. I have
> recompiled my kernel adding the following options:
>
> options         KDB
> options         DDB
> options         MP_WATCHDOG
> options         SW_WATCHDOG
>
> I am able to enter the debugger with ctrl+alt+esc from a console. So
> what I am trying to do is to have watchdogd time out and the debugger
> make a dump:
>
> ddb script kern.enter.watchdog=call doadump; reboot
>
> However, when I start X no timeout occurs, and the system stays freezed.
> Am I missing something on the workings of watchdogd?
>

What you're describing does not appear to be a kernel problem; it
sounds like the typical 'Xorg update from hell' problem most
experienced a while back.

Have a look at /usr/ports/UPDATING, and search for 'AllowEmptyInput'.

Adding the following to xorg.conf should correct the problem:

Section "ServerFlags"
  option "AllowEmptyInput" "off"
  option "AutoAddDevices" "off"
EndSection

HTH

-- 
Glen Barber