I couldn't imagine that silently ignoring the request to disable ASPM
would be the right thing, but I spent a long time experimenting with
Windows on qemu, and I think you're right.  Windows 7 also seems to
ignore the "PciASPMOptOut" directive when we don't have permission
to manage ASPM.  All the gory details are at
https://bugzilla.kernel.org/show_bug.cgi?id=57331

The current behavior is definitely confusing.  I hate to rename or change
pci_disable_link_state() because it's exported and we'd have to maintain
the old interface for a while anyway.  And I don't really want to return
failure to drivers, because I think that would encourage people to fiddle
with the Link Control register directly in the driver, which doesn't seem
like a good idea.

And you're also right that (as far as I know) there's not an actual
problem with the current behavior other than the confusion it causes.

So, how about something like the following patch, which just prints a
warning when we can't do what the driver requested?  I suppose this may
also be a nuisance, because users will be worried, but they can't actually
*do* anything about it.  Maybe it should be dev_info() instead.

Good for me - now I would be notified that something wrong happened.