The secondary MMC cannot be detected under Intel Fast Boot firmware on the FRI2. Tested the behavior with autobuilder03.jf.intel.com/pub/nightly-meta-intel/20120731-2/machines/fri2/core-image-sato-fri2.hddimg dmesg does not return any message when inserting the MMC. Also, EFI shell does not recognize the secondary MMC. Internal MMC does not present the described behavior.
Discussing with the firmware team. Will report back.
From the fastboot release notes: The connect command (with the -r option) forces the shell to connect all available device support drivers to all devices in the system. The process may take a few seconds (depending upon the nature of the external devices attached to the system). When complete, this command will allow the user access to all connected devices which the BIOS can support. Can you try running "connect -r" from the shell? Does the secondary mmc device appear in this case?
Being worked on by the fastboot team.
This is resolved in the 1018 build.
Behavior is still encountered with http://autobuilder03.jf.intel.com/pub/nightly-meta-intel/20121102-2/machines/fri2/ core-image-sato-sdk image.
.
Alex, note this is a firmware issue, not a Linux issue. As it is beyond the scope of what the Yocto Project developers can address, I'm closing as "INVALID" for lack of a better resolution.