Re: [PATCH 2/2] iio: dac: add support for Microchip MCP48FEB02

Ariana.Lazar
2026-04-24T13:31:08Z

Hi Jonathan,

>
> The statement above about it not being possible to use the internal
> band gap
> if a vref is wired leaves me with more questions about this.
>
> I'm a bit concerned about cases like:
>
> Vref is wired and eeprom is set for internal reference.   Should we
> be very careful to not enable vref until that situation is resolved?
> It might be on anyway but we can at least make sure we are reponsible
> for turning it on.
>
> Maybe the chip has sufficient protective elements to cope with that
> though obviously it won't give sensible output whilst this is true.
>
> If all those are fine, dev_info() makes sense to me.
> I wonder if we should return -EBUSY for attempts to read the voltage
> back whilst in this state as well?  Might provide some additional
> indication something is mismatched and we don't expect the device to
> work
> correctly.
>

There are 2 possible ways to handle this:

- Keep the current approach, since restoring a mismatching
configuration at power-up should not damage the device.
- As you suggested, only read the external regulator voltage at probe
to compute the related scale and enable the regulator when user space
first selects that scale.

In both cases, if you agree, I can return -EBUSY for RAW access until
the correct scale is written from user space.

I will also improve the current messages in order to ensure the user
sets the correct configuration before attempting to read voltage.

Best regards,
Ariana