Date: Tue, 12 Aug 1997 00:16:04 +0200 From: Stefan Esser <se@FreeBSD.ORG> To: "John W. DeBoskey" <jwd@unx.sas.com> Cc: freebsd-current@FreeBSD.ORG, Stefan Esser <se@FreeBSD.ORG> Subject: Re: Number of pci busses probed at boot time Message-ID: <19970812001604.36707@mi.uni-koeln.de> In-Reply-To: <199708111850.AA02267@iluvatar.unx.sas.com>; from John W. DeBoskey on Mon, Aug 11, 1997 at 02:50:15PM -0400 References: <199708111850.AA02267@iluvatar.unx.sas.com>
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On Aug 11, "John W. DeBoskey" <jwd@unx.sas.com> wrote:
> Hi,
>
> When I boot my system, the pci init code scans 255 pci busses
> looking for devices (which are found on bus 0 & 1). So, I thought
> I might reduce the number of pci busses probed...
Which version of FreeBSD do you use ?
> My confusion? Well, in pci.c, we have:
>
> static int
> pci_bushigh(void)
> {
> if (pic_cfgopen() == 0)
> return (-1);
> return (0);
> }
Ahhh, this appears to be -current ...
> and the return value is used in:
>
> int
> pci_probe(pciattach *parent)
> int bushigh;
> int bus = 0;
>
> bushigh = pci_bushigh();
> while (bus <= bushigh) {
> ...
>
>
> So, how is the system finding ANY pci busses? The code above
> seems to only return 0 or -1. Could someone enlighten me please?
Sure! There are two ways to find the number of PCI
buses:
1) Call the PCI BIOS.
2) Just check whether there is PCI to PCI bridge
and which bus numbers are behind it.
For various reasons I prefer method 2), although
there is now BIOS32 support in FreeBSD, which does
allow to use 1) as well ...
Seems you got the number 255 as that of the highest
bus behind some PCI to PCI bridge in a chip-set
register, and the probe code obeys this value and
scans all buses in between. I have thought about
stopping the scan, if no single device was found
on some PCI bus, but decided that this was bad,
since a PCI extender box with no cards in it would
have exactly that effect.
Do you by chance have a PPro system with two PCI
buses directly attached to the CPU ?
If yes, then check out the code in pcisupport.c,
functions fixbushigh_orion and fixbushigh_i1225.
Can you please check what:
# pciconf -r pci0:xx:0 0x48
returns on your system, if you replace xx with the
PCI slot number of your host to PCI bridge(s) ?
(On an Orion system, there are typically two host
to PCI bridge chips.)
Regards, STefan
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