6 Limitations

The driver has below limitations on supporting MMC over SPI bus interface.

• Clock configuration: The SAMA5D27 SOM1 reference platform restricts the maximum clock speed to 25MHz. For a throughput-centric evaluation the SAMA5D4 Xplained pro reference platform is recommended.

• MMC-SPI Card-Detection: The MMC-SPI does not support hotplug (insert/remove) functionality.

  Troubleshooting: SPI drivers reload after sideloading.

  Since hot-plug is not support for the ‘mmc-spi’ bus interface, it is recommended that the host software reloads the ‘mmc-spi’ and ‘wilc-sdio’ kernel modules after performing a firmware sideload operation.

  $ rmmod wilc-sdio
  $ rmmod mmc-spi
  $ modprobe wilc-sdio
  $ modprobe mmc-spi

• WILCS02 MMC-SPI can conflicts with SDCard (rootFS): To avoid the MMC conflict, it is recommended to keep WILCS02 Add-on boad connected to the Host MPU board before powering on the board.
• SPI-DMA: The DMA doesn't work over the MMC-SPI on the refernce board. It is required to disable the DMA initialization sequence in the mmc_spi_probe() API of mmc-spi.c host file.

  	/* status = mmc_spi_dma_alloc(host);
  	if (status)
  		goto fail_dma; */