The ath9k_htc driver has been included in the mainline Linux kernel since version 2.6.35 so having a new enough kernel really isn't the issue.
The real issue is finding a kernel that hasn't blacklisted loading the firmware, since it used to be proprietary. Which will do that? Well, none of mine do. Also, none of the Trisquel ones will either -- once they're updated. The other issue is getting the firmware into your machine, in /lib/firmware. The actual kernel version's not so important.
