Re: [PATCH v3 2/2] iio: adc: Add Intel Dollar Cove TI PMIC ADC driver

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Tue, 29 Jul 2025 12:50:36 -0500
David Lechner <dlechner@baylibre.com> wrote:

> On 7/27/25 4:06 PM, Hans de Goede wrote:
> 
> ...
> 
> > +static const struct iio_chan_spec dc_ti_adc_channels[] = {
> > +	{
> > +		.indexed = 1,
> > +		.type = IIO_VOLTAGE,
> > +		.channel = DC_TI_ADC_VBAT,
> > +		.address = DC_TI_ADC_DATA_REG_CH(0),
> > +		.datasheet_name = "CH0",
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> > +				      BIT(IIO_CHAN_INFO_SCALE) |
> > +				      BIT(IIO_CHAN_INFO_PROCESSED),
> > +	}, {
> > +		.indexed = 1,
> > +		.type = IIO_TEMP,
> > +		.channel = DC_TI_ADC_PMICTEMP,
> > +		.address = DC_TI_ADC_DATA_REG_CH(1),
> > +		.datasheet_name = "CH1",
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +	}, {
> > +		.indexed = 1,
> > +		.type = IIO_TEMP,
> > +		.channel = DC_TI_ADC_BATTEMP,
> > +		.address = DC_TI_ADC_DATA_REG_CH(2),
> > +		.datasheet_name = "CH2",
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +	}, {
> > +		.indexed = 1,
> > +		.type = IIO_TEMP,
> > +		.channel = DC_TI_ADC_SYSTEMP0,
> > +		.address = DC_TI_ADC_DATA_REG_CH(3),
> > +		.datasheet_name = "CH3",
> > +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> > +	}
> > +};  
> 
> Question for Jonathan: If we don't know the scale on these
> temperature channels, should we implement IIO_CHAN_INFO_SCALE
> and just always return an error? My understanding is that
> by not implementing it, the scale is assumed to be 1, which
> likely isn't correct in in this case.

Good question.   We have quite a bit of precedence of just
not providing scale in these cases.  The docs for the main block of _scale
do say

"If known for a device, scale to be applied to <type>Y[_name]_raw
 post addition of <type>[Y][_name]_offset in order to obtain the
 measured value in <type> units as specified in
 <type>[Y][_name]_raw documentation. "

Rather than trying to fix all those, shall we tweak the docs
to say that scale is assumed to be 1 if offset is provided?

If neither is there, the channel can be _PROCESSED anyway.

Your suggestion of returning an error would have been somewhat neat
long ago, but now I think it will just be too confusing for userspace.

Jonathan

> 
>