On Oct 29, 2004, at 7:18 AM, Riccardo Mottola wrote:

> ah, to whom was concerned about the two PCI bridges. OF didn't see it !
> dev / ls showed only one pci. I cleaned pram, reset the OF parameters
> and now I see it both from OF as from the kernel. But at the next
> reboot... it seems to be gone again. I really suspect that OF disables
> unused PCI things ?

I see the same thing on my PowerMac 7300 (only one PCI bus), where the 
mesh is scsibus2.  scsibus0 is a (now finally working again) Adaptec 
2940UW.
sd0 at scsibus0 target 0 lun 0: <IBM, DCHS04U, 6464> disk fixed
sd0: 4303 MB, 6077 cyl, 9 head, 161 sec, 512 bytes/sect x 8813870 
sectors
sd0: sync (100.00ns offset 8), 16-bit (20.000MB/s) transfers, tagged 
queueing
sd1 at scsibus2 target 1 lun 0: <IBM, DCAS-32160, S65A> disk fixed
sd1: drive offline

Note, that this drive still works fine, even if it's the root drive.  
It just takes a little longer for the kernel to try the different 
filesystem types after renegotiating with the drive.  Also, this drive 
had no sync problems with 1.6.2:
scsibus0: waiting 2 seconds for devices to settle...
sd0 at scsibus0 target 0 lun 0: <IBM, DCHS04U, 6464> SCSI2 0/direct 
fixed
sd0: 4303 MB, 6077 cyl, 9 head, 161 sec, 512 bytes/sect x 8813870 
sectors
sd0: sync (100.0ns offset 8), 16-bit (20.000MB/s) transfers, tagged 
queueing
scsibus1: waiting 2 seconds for devices to settle...
scsibus2: waiting 2 seconds for devices to settle...
sd1 at scsibus2 target 1 lun 0: <IBM, DCAS-32160, S65A> SCSI2 0/direct 
fixed
sd1: 2063 MB, 8188 cyl, 3 head, 172 sec, 512 bytes/sect x 4226725 
sectors

HTH,
   -- MW