> > I think it doesn't make sense to print a dev_err and return ENODEV which
> > is treated by the driver core as a non-error. It means "not present, but
> > OK". You probably want other error codes here.
> 
> How about -EINVAL for these -ENODEV error codes? Do you have any suggestion?

-EINVAL will do, I would go for -ENOENT, probably. But it doesn't matter
much.