[eerimoq]

The goal is to not configure the MMC at all in Linux, but just rely on the bootloader has already configured it.

Btw, where can I find the spec? And where in the spec can I read about this? Is this true even if we know the MMC supports 52 MHz?

[OnACoffeeBreak]

https://www.jedec.org/sites/default/files/docs/JESD84-B451.p...

You can use http://bugmenot.com/view/jedec.org to get free-to-use credentials.

The section in point is "A.6.1Bus initialization".

I'd say that if your MMC works fine going full-speed out of the gate and the IC on the board supports this speed, then you unlikely to encounter any issues.

[eerimoq]

Thank you very much. Very helpful answer. I'll continue to use 52 MHz until I encounter problems (if any).

[dmitrygr]

Spec says initialization shall be done at 400KHz or less. You can Google for sd spec

[eerimoq]

Will fix it at some point =)