Some MMC4.x cards might not be recognized correctly due to non-compliant response to CMD8 (SD_SEND_IF_COND/MMC_SEND_EXTCSD)

Swissbit MMC card is refused by initialization routine due to invalid response on CMD8.

The MMC driver utilize CMD8 to detect the card type (MMC/SD/SDHC/SDXC). This detection may fail for MMC 4.x cards, due to differences in handling of CMD8.
Since MMC 4.x specification, CMD8 is handled differently than in the SD 2.0 specification: In the SD protocol CMD8 is used to identify high capacity cards and it is send at the beginning of the initialization process. When CMD8 is getting a response it means that it is identified as a High Capacity card.
While SD1.xx and not-MMC4.x cards don't know CMD8, MMC4.x cards utilize CMD8 to retrieve the extended CSD register of the card.

As the Swissbit MMC4.x card response to CMD8 with bullshit data (0xFF pattern), initialization is refused by the driver. This might be a non-compliant behaviour, as some sources claim, that CMD8 is not allowed in idle state!

NOTE from http://guruce.com/blogpost/sdmmcandwindowsce:
CMD8 must be send after a CMD7 command which will place the card into "Tran" state. Since the SD bus driver doesn't do that the CMD8 will time out.