The PCI Utilities package contains a library for portable access to
PCI bus configuration registers and several utilities based on this
library.

Currently, pciutils work on all versions of Linux and they also have
somewhat experimental support for OpenBSD, FreeBSD, NetBSD, AIX, GNU
Hurd and Solaris/x86.  It should be very easy to add support for other
systems as well (volunteers wanted; if you want to try that, I'll be
very glad to see the patches and include them in the next version).

The utilities include:  (See manual pages for more details)

  - lspci: displays detailed information about all PCI buses and
    devices.

  - setpci: allows to read from and write to PCI device configuration
    registers. For example, you can adjust the latency timers with it.
    CAUTION: There is a couple of dangerous points and caveats, please
    read the manual page first!

  - update-pciids: download the current version of the pci.ids file.

On FabBSD you need to set sysctl machdep.allowaperture=2 in
/etc/sysctl.conf, and run lspci and setpci as root.