lspci is capable of showing you information about your PCI-bus, which you can use to determine the supported version. But it requires additional steps.
lspci and look for entries that contain something like
PCI bridge:. In those line(s) look for a number after a vendor name. That number is most likely the descriptor of your PCI bridge chipset, which you can look up with the searchengine of your choice with the added keyword "datasheet" to find - for example - a pdf from the manufacturer that lists its capabilities. This includes the supported pci version.
When I run
% lspci | grep "PCI bridge"
on my machine, that gives me two lines:
00:01.0 PCI bridge: Intel Corporation 82855PM Processor to AGP Controller (rev 03)
00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev 81)
the second one there looks like our chip because the description does not contain AGP ;-)
Now I search for the number after the vendorname:
That gives me a .pdf download from the intel website. In that PDF I search for
specification and find
Supports PCI Rev 2.2 Specification
Tadaa thats the supported version for all ports that depend on that buscontroller
dmidecode is useful whenever you need information about such things as voltages or additional non-standard capabilities like SMBus support.