Protocol probe results caching

Per Bjørn's email in the MM mailing list.

How about caching protocol probe results and skipping the full probe if a match is found?

Keying the cached data and knowing when to ignore the cache is probably the hard part. But I believe there is a lot to gain for normal use cases. Most people don't use lots of modems. Many systems will have the same modem connected to the same port for extended periods. Some system designs cause the MM probing to run very often, "always" returning the same result. Looking at my laptop for example: It turns off power to the internal wwan slot on suspend. So MM must probe the modem on every resume, causing a significant delay from the system appears to be up until the network is up again.

The protocol probes are obviously a waste of time in this case. Unless I am messing with drivers or descriptors :-) But that's easy to detect. You could just ignore the protocol cache if any of the udev data changed. It would still be a large win for most cases.