How do drummers earn the title of composer?

I was just wondering how a drummer earns a composer credit, since I don't really know how it works. I'll use two of my favorite bands as examples: When he was in Mars Volta, Jon Theodore didn't earn a composer credit, yet I'm sure he was the one who invented the drum parts. Yet Chad Smith of the Chili Peppers has a composer credit, but I couldn't see him writing anything more than just the drum part. Any distinction?