Where is this kernel flag (pcie_aspm) documented? I'm sure it does something, and I just turned it off to get wired Ethernet driver (e1000e) working.
So, the first hit on Google for "pcie_aspm" is:
and that documentation is in the current kernel
Documentation/kernel-parameters.txt, where it says:
pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power Management. off Disable ASPM. force Enable ASPM even on devices that claim not to support it. WARNING: Forcing ASPM on may cause system lockups.
And in turn, google for "pcie active state power management" leads to PCI Express* Architecture Power Management document, which explans that ASPM does pretty much what the name implies.