Don't delete this

or this

I think it might be cleaner to come in "over the top" and avoid adding the extra enum value. A direct getter/setter to the state variable would work, so your call from diskio.c would look like:

MXC_SDHC_Lib_Write(sector, (void *)buff, count, MXC_SDHC_Get_DataWidth())

Usually you're not gonna change your data width more than once at run-time, so a mechanism for setting the default value might be better implemented as a build-time option. Users can use the setter API you've exposed on initialization.

This would let us avoid these modifications to sdhc_lib.c, since the data width is already an arg to the SDHC functions

That is what is set as in diskio.c. The point of doing this extra step was to not break the API if someone uses it directly. Since Get/Set default data width doesn't really do more than allow us to get it at the higher level. It is a little Awkard that you set it and then have to pass it anyway. I am fine deleting those modifications though.