> I think you are right that the controller does not seem to support
> additional I2C features in addition to SMBUS.
> 
> However, my concern of switching to the smbus_xfer API is:
> 
> 1) Some customers might have used I2C_RDWR based API from i2cdev. Changing
> from master_xfer to smbus_xfer may break the existing applications that are
> already developed.

Well, given that you add new quirks in the original patch here, you are
kind of breaking it already. Most transfers which are not SMBus-alike
transfers would now be rejected. For SMBus-alike transfers which are
sent via I2C_RDWR (which is ugly), I have to think about it.

> 2) The sound subsystem I2C regmap based implementation seems to be using
> i2c_ based API instead of smbus_ based API. Does this mean this will also
> break most of the audio codec drivers with I2C regmap API based usage?

I don't think so. If you check regmap_get_i2c_bus() then it checks the
adapter functionality and chooses the best transfer option then. I may
be missing something but I would wonder if the sound system does
something special and different.