I have some experience with this from a few years ago when I tried to set up a media server. Back then, you used "dvb://" for anything digital, including ATSC and ISDB (since its mostly Europeans working on it, it kind of makes sense). One problem is that (almost?) all devices require a channel scan before they start working; there are dedicated V4L2 tools for this, as I recall--though I can't recall the names of those tools. :\
More recently, I remember reading that the analog and digital parts have been merged so you now only need the "dvb://" to access anything, but the part about scanning channels first is part of the hardware (or at least its firmware) itself, and still needs to be done.
I hope this helps, although this info is probably outdated a bit.
P.S. What device do you have? Are you sure its supported?
P.P.S. Main TV software page: http://linuxtv.org/wiki/index.php/TV_Related_Software