Re: Quad Pentium Pro dual PCI buses, cat /proc/pci misses one bus

Gabriel Paubert (paubert@iram.es)
Fri, 26 Dec 1997 20:04:28 +0100 (MET)


On Thu, 25 Dec 1997, Brynn Rogers wrote:

>
> I have a Quad PPro (I think the motherboard is a ALR/DataGeneral product)
> that doesn't show devices on the second pci bus in /proc/pci.
> But they obviously work, because the 2940uw works fine and shows up
> in /proc/scsi/aic7xxx/0 and is completly missing from /proc/pci.
>
> The Motherboard has the 450GX chipset (Orion), and I suspect that
> one of the devices that /proc/pci does see is really a pci-pci bridge
> that isn't recognized.
>

Nope, the Orion chipset has a mode of operation in which there are two
processor to PCI bridges. There is no no need for a PCI to PCI bridge
to have two PCI buses in this case and that's why it is not detected.
(The 450GX chipset allows up to 2 PCI bridges, 2 memory controllers and 4
processors, this makes at least 8 loads on the bus and that's probably
why Intel does not want to push bus frequencies above 66 MHz.)

That's why you see two host bridges in your cat /proc/pci. But listing
what is behind the second bridge would require special casing in the pci
code to handle this case. The bus number corresponding to the second
bridge (device 26) is located in register at offset 0x4a in its
configuration space.

It seems at least that your PCI BIOS works properly and the device is found
when scanning the bus by BIOS calls :-)

> I am now running 2.1.74 in this box, and I also ran 2.0.30.
> /proc/pci gives this:
> PCI devices found:
> Bus 0, device 26, function 0:
> Host bridge: Intel Orion P6 (rev 4).
> Medium devsel. Master Capable. Latency=72.
> Bus 0, device 25, function 0:
> Host bridge: Intel Orion P6 (rev 4).
> Medium devsel. Master Capable. Latency=72.
> Bus 0, device 20, function 0:
> RAM memory: Intel 82450GX Orion P6 (rev 4).
> Fast devsel. Fast back-to-back capable.
> Bus 0, device 13, function 0:
> VGA compatible controller: ATI 210888GX (rev 3).
> Medium devsel. IRQ 40.
> Non-prefetchable 32 bit memory at 0xfd000000 [0xfd000000].
> Bus 0, device 3, function 0:
> IDE controller: OPTi 82C621 (rev 0).
> Medium devsel. Fast back-to-back capable.
> Bus 0, device 2, function 0:
> Non-VGA device: Intel 82375EB (rev 21).
> Medium devsel. Master Capable. Latency=248.
>
> Any point in getting /proc/pci to work right?
>
> P.S. The CPU's are PPRO 166/512K, and for giggles I tried 200 and 233 MHZ
> out, both of which worked perfectly. I run it at 166 because I don't
> want ANY problems.
>
> P.P.S. any possibility of mounting the DGUX filesystem? (DataGeneral)
>
> Brynn Rogers
> http://www.winternet.com/~brynn to see my triplets!
>
>