Re: [PATCH v7 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

TL;DR: Will switch to voltageY-voltageZ ABI.

On 07/18, Jonathan Cameron wrote:
> On Fri, 17 Jul 2026 13:38:07 -0300
> Marcelo Schmitt <marcelo.schmitt1@gmail.com> wrote:
> 
> > On 07/16, sashiko-bot@kernel.org wrote:
> > > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> > > - [Medium] The `LTC2378_DIFF_CHANNEL` macro defines an IIO channel that is intended to be differential but lacks the `.differential = 1`, `.indexed = 1`, `.channel = 0`, and `.channel2 = 1` attributes.
> > > --
> > > 
> > > --- Patch [2]: [PATCH v7 2/4] iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs ---
> > > commit 5710d5f25b45906977e2522567c1964b1d3219f8
> > > Author: Marcelo Schmitt <marcelo.schmitt@analog.com>
> > > 
> > > iio: adc: ltc2378: Add support for LTC2378-20 and similar ADCs
> > > 
> > > This commit adds a new driver for the Analog Devices LTC2378-20 and
> > > similar analog-to-digital converters.
> > >   
> > > > diff --git a/drivers/iio/adc/ltc2378.c b/drivers/iio/adc/ltc2378.c
> > > > new file mode 100644
> > > > index 0000000000000..5600c820c7f45
> > > > --- /dev/null
> > > > +++ b/drivers/iio/adc/ltc2378.c
> > > > @@ -0,0 +1,416 @@  
> > > [ ... ]  
> > > > +#define LTC2378_DIFF_CHANNEL(_sign, _real_bits, _storage_bits)			\
> > > > +{										\
> > > > +	.type = IIO_VOLTAGE,							\
> > > > +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |				\
> > > > +			      BIT(IIO_CHAN_INFO_SCALE),				\
> > > > +	.scan_index = 0,							\  
> > > 
> > > [Severity: Medium]
> > > Does this macro need to set .differential = 1, .indexed = 1, .channel = 0,
> > > and .channel2 = 1? The name suggests these are differential channels, but
> > > without these attributes, the IIO ABI will expose them as single-ended
> > > (e.g., in_voltage_raw instead of in_voltage0-voltage1_raw).  
> > 
> > For parts with multiple inputs and configurable differential channels (e.g.
> > AD4130-8, MCP3561/2/4R, NAFE13388 [1, 2, 3]), the voltageY-voltageZ ABI helps
> > clarifying what physical inputs make up a channel. For differential only parts,
> > the ABI seems to be flexible by only requiring a 'consistent labeling' (either
> > voltageY or voltageY-voltageZ IIUC). Will set the channel with the differential
> > ABI if maintainers believe that's the best way to have it. Might slightly tweak
> > the channel macros to keep .differential = 0 for pseudo-differential chips
> > (e.g.LTC2369-18).
> 
> Whilst I get your point on differential only cases not really requiring the
> specification of two inputs, I think that does provide a simple indication
> to users that they are differential channel.
Agree. The first ADCs I've worked with were single-ended so having to provide
the negative input when working with differential ones was something noticeable
to me. Though, one applications engineer once called me out for the
voltageY-voltageZ naming arguing that a differential channel provided only one
input to his application and thus it should be labeled only 'voltageY' or even
just 'voltage'. Despite understanding that argument, I share the opinion 
that an indication of differential channel is helpful. Anyways, besides the
possibility for application to display channel names differently in user space,
I see we now have .read_label so the whole discussion seems pointless.

> 
> I would prefer that we make them 'look' like differential channels so make up
> a suitable number for the negative side.

Would it make sense to adjust the ABI doc to encourage the dual numbering for
differential channels? So I don't fall the temptation of single index in the
future :)

Thanks,
Marcelo