On Tue, Dec 01, 2020 at 01:41:33PM +0800, Shane Chien wrote:

However, if the device is not given a comaptible, of_node of struct device is null. I cannot use devm_iio_channel_get such iio interface to get auxadc value from iio channel. Because during using devm_iio_channel_get, of_node of mt6359-sound is a input parameter of of_iio_channel_get_by_name. If the of_node is null, devm_iio_channel_get will eventually return ENODEV error.

I would expect the IIO channel to be requestable using the top level device for the MFD - part of the deal here is that the function drivers for the MFD know they're part of the MFD so can look at their parent device for some things (eg, this is how regmaps are normally obtained).