Re: [PATCH v2 7/7] iio: temperature: ltc2983: Add support for ADT7604

[Liviu Stan <liviu.stan@analog.com>]

On Sat, 16 May 2026 18:12:50 +0100 Jonathan Cameron <jic23@kernel.org> wrote:
> > 
> >  drivers/iio/temperature/ltc2983.c | 401 ++++++++++++++++++++++++++++--
> >  1 file changed, 386 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/iio/temperature/ltc2983.c b/drivers/iio/temperature/ltc2983.c
> > index bf435e965c6d..acd043ed62f5 100644
> > --- a/drivers/iio/temperature/ltc2983.c
> > +++ b/drivers/iio/temperature/ltc2983.c
> > @@ -28,6 +28,8 @@
> >  #define LTC2983_STATUS_REG			0x0000
> >  #define LTC2983_TEMP_RES_START_REG		0x0010
> >  #define LTC2983_TEMP_RES_END_REG		0x005F
> > +#define ADT7604_RES_RES_START_REG		0x0060
> > +#define ADT7604_RES_RES_END_REG			0x00AF
> >  #define LTC2983_EEPROM_KEY_REG			0x00B0
> >  #define LTC2983_EEPROM_READ_STATUS_REG		0x00D0
> >  #define LTC2983_GLOBAL_CONFIG_REG		0x00F0
> > @@ -186,17 +188,43 @@ enum {
> >  	LTC2983_SENSOR_SENSE_RESISTOR = 29,
> >  	LTC2983_SENSOR_DIRECT_ADC = 30,
> >  	LTC2983_SENSOR_ACTIVE_TEMP = 31,
> > +	/* Sensor types for some parts only; map to RTD_CUSTOM/THERMISTOR_CUSTOM in HW */
> > +	LTC2983_SENSOR_COPPER_TRACE = 32,
> > +	LTC2983_SENSOR_LEAK_DETECTOR = 33,
> Given you care about being in range of this I'd add
> 	LTC2983_SENSOR_NUM
> >  };
> 
> > @@ -1329,7 +1649,7 @@ static int ltc2983_parse_fw(struct ltc2983_data *st)
> >  	if (!st->sensors)
> >  		return -ENOMEM;
> >  
> > -	st->iio_channels = st->num_channels;
> > +	st->iio_channels = 0;
> >  	device_for_each_child_node_scoped(dev, child) {
> >  		struct ltc2983_sensor sensor;
> >  
> > @@ -1357,7 +1677,13 @@ static int ltc2983_parse_fw(struct ltc2983_data *st)
> >  			return dev_err_probe(dev, ret,
> >  				"adi,sensor-type property must given for child nodes\n");
> >  
> > -		dev_dbg(dev, "Create new sensor, type %u, chann %u",
> > +		if (sensor.type > LTC2983_SENSOR_LEAK_DETECTOR ||
> 
> To make it easier to extend in future, perhaps add the NUM entry I mention
> above then >= to it here.
> 

This makes sense. I will change in v3. Thanks!

> > +		    !(st->info->supported_sensors & BIT_ULL(sensor.type)))
> > +			return dev_err_probe(dev, -EINVAL,
> > +					     "sensor type %d not supported on %s\n",
> > +					     sensor.type, st->info->name);
> > +
> > +		dev_dbg(dev, "Create new sensor, type %u, channel %u",
> >  			sensor.type, sensor.chan);
> >  
> 
> > @@ -1445,8 +1782,9 @@ static int ltc2983_eeprom_cmd(struct ltc2983_data *st, unsigned int cmd,
> >  
> >  static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
> >  {
> > -	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status;
> >  	struct device *dev = &st->spi->dev;
> > +	u32 iio_chan_t = 0, iio_chan_v = 0, iio_chan_r = 0, iio_chan_c = 0;
> > +	u32 chan, iio_idx = 0, status;
> >  	int ret;
> >  
> >  	/* make sure the device is up: start bit (7) is 0 and done bit (6) is 1 */
> > @@ -1493,8 +1831,26 @@ static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
> >  		    !assign_iio)
> >  			continue;
> >  
> > +		/*
> > +		 * Copper trace and leak detector sensors without a custom table
> > +		 * produce only a resistance result; the chip does not populate
> > +		 * the temperature result register. Emit only an IIO_RESISTANCE
> > +		 * channel in this case.
> 
> Do we care?  That is are they useful without the table? We could just make it
> required in the binding.
> 

The datasheet specifies the table is optional. But more practically, in order to
be able to add accurate values to the custom table, the users first need to measure
the sensor's resistance at multiple known conditions, so I think the resistance-only
output is useful during that characterization phase, before the table exists. Making
it required would force users to provide placeholder values just to get the driver
to probe.

Thanks,
Liviu