cvs commit: src/sys/dev/pci pci.c
jhb at freebsd.org
Mon Feb 4 15:00:37 PST 2008
On Monday 04 February 2008 10:34:09 am Scott Long wrote:
> John Baldwin wrote:
> > On Friday 01 February 2008 09:18:38 pm Scott Long wrote:
> >> John Baldwin wrote:
> >>> jhb 2008-02-01 20:31:09 UTC
> >>> FreeBSD src repository
> >>> Modified files:
> >>> sys/dev/pci pci.c
> >>> Log:
> >>> Relax the check for a PCI-express chipset by assuming the system is a
> >>> PCI-express chipset (and thus has functional MSI) if there are any
> >>> PCI-express devices in the system, not requiring a root port device.
> >>> With PCI-X the chipset detection has to be very conservative because
> >>> are known systems with PCI-X devices that do not appear to have PCI-X
> >>> chipsets. However, with PCI-express I'm not sure it is possible to
> >>> a PCI-express device in a system with a non-PCI-express chipset. If
> >>> assume that is the case then this change is valid. It is also
> >>> for at least some PCI-express systems that don't have any devices with
> >>> a root port capability (some ICH9 systems).
> >>> MFC after: 1 week
> >>> Reported by: jfv
> >>> Revision Changes Path
> >>> 1.357 +2 -5 src/sys/dev/pci/pci.c
> >> It's certainly possible for a PCI-X device to be plugged into a PCI-only
> >> system; PCI-X is backwards compatible at an electrical an protocol level
> >> with 3.3V PCI. So yes, you will see PCI-X extcaps on PCI-X cards even
> >> if there is no PCI-X bridge.
> >> I'm sure there are fun, interesting, and highly obtuse ways to get a
> >> PCI-E device onto a system with no PCI-E root complex. I do agree with
> >> your implicit statement to not worry about such an edge case, at least
> >> not until such an edge case becomes a demonstrated reality. What does
> >> worry me is that Intel would release PCI-E chipsets without an
> >> advertised root complex. That would seem to blatantly violate the spec.
> >> Does Jack have confirmation that this is really the case? If so, what
> >> else is being played fast-and-loose with that we should know about?
> > It's not that it isn't advertising a root complex but isn't advertising a
> > root _port_ unless there is a PCI-e expansion card plugged in. I guess
> > internal PCI-e devices aren't connected via a port? It does seem
> > inconsistent as my laptop with no external PCI-e slots has root ports
> > capabilities on PCI-PCI bridges off of bus 0 that service internal
> Ok, funky. So there are onboard PCIe devices, but it only advertises a
> port if there are external devices. I'm not clear on the technical
> distinction there either.
Correct, I find it quite odd myself and had assumed that you would always have
root ports. I was quite surprised to learn otherwise. :-/
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