AVR32: Mizar32: SD card support for RT-Thread

[ramangopalan]

Dear RT-Thread community, Greetings!

I trust you're all doing so well. While I have some time today, I was
thinking of implementing support for the SD card interface for the
Mizar32 platform. I haven't started writing anything yet. I am just
exploring the codebase for now.

The Mizar32 platform supports SD card access over SPI. Do I have to
necessarily implement a drv_spi.c for Mizar32 for this? I have seen
code from bsp/lm3s8962 here [1]. May I implement something similar for
Mizar32? I am not sure if DFS works on the RT-Thread SPI device
drivers.

Second: Is is alright to enable RT_USING_DFS by default for Mizar32?

Good day!

References:
[1]: https://github.com/RT-Thread/rt-thread/blob/master/bsp/lm3s8962/drivers/sdcard.c