modular Xorg on hp 6172sf (switchable graphics)

[rakakabe super <rakakabe%live.fr@localhost>]

Hi everyone,
 
I have some trouble running modular Xorg 1.6.5 on a recent laptop, 
and I suspect the famous 'switchable graphics'.
 
Even if 'pcictl /dev/pci0 list' recognizes the 2 cards:
 
000:02:0: Intel product 0x0116 (VGA display, revision 0x09)
001:00:0: ATI Technologies product 0x6740 (VGA display)
 
they share the same display output as 'dmesg' reports (my interpretation):
 
acpivga0 at acpi0 (PEGP): ACPI Display Adapter
acpiout0 at acpivga0 (DD01, 0x0100): ACPI Display Output Device
acpiout1 at acpivga0 (DD02, 0x0410): ACPI Display Output Device
acpivga0: connected output devices:
acpivga0: 0x0400: Unknown Output Device, head 0
acpivga1 at acpi0 (GFX0): ACPI Display Adapter
acpiout8 at acpivga1 (DD01, 0x0100): ACPI Display Output Device
acpiout9 at acpivga1 (DD02, 0x0410): ACPI Display Output Device
acpivga1: connected output devices:
acpivga1: 0x0400: Unknown Output Device, head 0
 
but modular Xorg 1.6.5 can't decide which one to use, as shown in Xorg.0.log:
 
(!!) More than one possible primary device found
(--) PCI: (0:0:2:0) 8086:0116:103c:3388 rev 9, Mem @ 0xc0000000/4194304, 
0xb0000000/268435456, I/O @ 0x00006000/64
(--) PCI: (1:1:0:0) 1002:6740:103c:3388 rev 0, Mem @ 0xa0000000/268435456, 
0xc6500000/131072, I/O @ 0x00005000/256, BIOS @ 0x????????/131072
 
As a result, I've only got a blank screen and Crtl+Alt+Backspace didn't work 
(I can't go back to my console). 
On top of that, the only option I've got in the BIOS about the switchable 
graphics
mode is dynamic (seamlessly switch to internal or external graphics adapter) or
fixed mode (graphics adapter switch is based on AC/DC transition or user 
selectable
option under OS - BIOS description).
 
Any hint on how to disable one of the graphic cards, or the only way is a 
similar 
stuff described in http://linux-hybrid-graphics.blogspot.com/ ? 

My config: HP Pavilion dv6-6172sf + NetBSD 5.99.55 (GENERIC) +
pkgsrc 2010Q2 + modular Xorg 1.6.5.