cvs commit: src/sys/dev/pci pci.c

Scott Long scottl at
Mon Feb 4 07:34:16 PST 2008

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 there
>>>   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 have
>>>   a PCI-express device in a system with a non-PCI-express chipset.  If we
>>>   assume that is the case then this change is valid.  It is also required
>>>   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 devices.

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.


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