I did not realize this, but MMC/SD cards are not supported in the default DragonFly kernel. Or at least, they weren’t until now. (also committed to 2.12)
Update: PCI-based MMC/SD readers, specifically. USB ones were already recognized as umass devices.
It is one of the things I like so much about DragonflyBSD compared with the other BSD’s,
GENERIC is not full of junk and yet contains things that you actually need.
FreeBSD’s is a total mess!