[...]

quoted

quoted

quoted

Could this be implemented by regulator API? From patch set 3/3, the
pxa1928
voltage_switch hook is to operate the IO pad registers, this seems not
belong
to the SDHC IP core.

Not quite sure whether regulator would be right fit for this.

 From the patche[3/3], this can be achieved by abstracting the IO PAD as
regulators
then, we may not need to touch the core sdhci.c. But I'm not sure whether
this
is the good solution or not.

Exactly...

quoted

sdhci Maintainers and experts may have better
suggestions.

Thats is the reason I stamped it as a RFC :)

[...]

From an mmc core perspective it would be preferred if you implement

this as a regulator (vqmmc).

Especially since we will soon have an API for how to set the I/O
voltages - and the intelligence within that API is not something we
would like to implement for each and every host driver.
https://lkml.org/lkml/2015/8/31/367

Kind regards
Uffe