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
And in turn, google for "pcie active state power management" leads to http://www.intel.com/technology/pciexpress/devnet/docs/PCIExpress1ArchPowerMgmt.pdf, which explans that ASPM does pretty much what the name implies.