> BTW I think the DTS additions don't look too bad? It is a grey area,
> though...
> 
>  &i2c3  {
>         pinctrl-0 = <&i2c3_pins>;
>         pinctrl-names = "i2c-pwr";
> +
> +       enable-host-notify;

I got another idea. What about a boolean binding "smbus"?

This describes the bus as SMBus (and not I2C bus), so the additional
SMBus restrictions/requirements apply. HostNotify is required for SMBus,
so address 0x08 can't be used. Alert is optional, but still it uses a
reserved address. SMBus timeouts maybe can be handled through this as
well (there is the HWMON specific "smbus-timeout-disable" so far).

So, we have one simple binding for HostNotify and Alert which really
describes the HW.