Wow, it’s been a long time since I’ve written anything, but I figure this is a good enough reason to do so. The SD specification has been available for quite a while now, but up until now, the MMC specification has had a $5000 price tag stuck to it. This has kept it out of most people’s hands, although Nokia were kind enough to buy a copy for Pierre. However, they have now made the latest version (4.3) available without charge. I believe this change of heart stems from the standardisation of eMMC through JEDEC (They still charge for their other specs). Despite the focus on eMMC, it is the full specification (minus the section on using MMC over SPI which they have declared obsolete; this isn’t a big deal as there’s enough documentation around explaining how MMC over SPI works).
What does this mean? Not that much in terms of Linux kernel support for MMC; Pierre already used his copy of the 4.2 spec to fix any problems and 4.3 doesn’t really add anything new that affects us. eMMC (Embedded MMC) is mostly just a new form-factor and doesn’t appear differently from a regular card. The one substantive new feature is the introduction of a special ‘boot partition’ which are accessed in a simplified way – presumably this was added to make it easy for a bootloader to load an OS off an eMMC. I don’t really see much demand emerging for this, so we have no immediate plans to support it (and good luck finding a card with a boot partition!) but if the need arose, we’d be able to do it.
So, nothing’s changed in practical terms, but it’s still helpful for us that the spec is now freely available; however, it probably won’t do much to help MMC against the SD juggernaut. Anyone seen a high capacity MMC card despite them being ‘available’ for over two years now? Thought so.