On Mon, May 22, 2017 at 12:44:14PM +0000, Avri Altman wrote:

Those debugfs entries are there for ages, and there are some user-space utilities,
 e.g. for benchmarking etc. that count on it being there, 
 as the key identification criteria if a mmc device is present.

debugfs is an optional feature not present on many systems, and
explicitly not considered a kernel ABI.