Re: [PATCH v3 8/8] iio: temperature: ltc2983: Add support for ADT7604

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 21 May 2026 19:43:01 +0300
Liviu Stan <liviu.stan@analog.com> wrote:

> The ADT7604 shares the same die as the LTC2984. It repurposes the
> custom RTD sensor type (18) as a copper trace resistance sensor
> and the custom thermistor type (27) as a leak detector, and
> removes thermocouple, diode and direct ADC sensor types.
> 
> Two new software sensor type values are introduced
> (LTC2983_SENSOR_COPPER_TRACE = 32, LTC2983_SENSOR_LEAK_DETECTOR = 33)
> that map to the hardware register values 18 and 27 respectively.
> Dedicated structs (ltc2983_copper_trace, ltc2983_leak_detector) and
> parser functions are added rather than extending the existing RTD and
> thermistor paths, as the hardware configuration bits are fully
> hardcoded and several RTD/thermistor properties would need to be
> explicitly forbidden or ignored.
> 
> Custom RTD (type 18) becomes the copper trace sensor. Sensor
> configuration bits are hardcoded to 0b1001 per the datasheet.
> Two variants are supported via the adi,copper-trace-sub-ohm DT
> property: sub-ohm traces (< 1 ohm) have bits 17:0 cleared with no
> excitation current or custom table; standard traces (> 1 ohm) have
> a required resistance-to-temperature table.
> 
> Custom thermistor (type 27) becomes the leak detector. Sensor
> configuration bits are hardcoded to 0b001. The custom table uses
> a resolution of 16 instead of 64, and is specified via the
> required adi,custom-leak-detector DT property.
> 
> Both sensor types expose an IIO_RESISTANCE channel reading from
> the resistance result register bank (0x0060-0x00AF). Added a
> "base" parameter to the LTC2983_RESULT_ADDR macro and a "base_reg"
> parameter to the ltc2983_chan_read function so we can read from
> both result register banks. The resistance register encodes the
> measured resistance with 10 fractional bits, so dividing by 1024
> gives ohms. Since the sense resistor is specified in ohms, the
> output is in ohms for both sensor types and a single 1/1024
> scale applies to both. For > 1 ohm copper traces and for leak
> detectors, a secondary channel also appears: IIO_TEMP
> (millidegrees Celsius) for copper trace and IIO_COVERAGE (percent)
> for leak detector.
> 
> The ltc2983_chip_info struct is extended with a u64 supported_sensors
> bitmask using BIT_ULL() to safely represent the new sensor type bits
> 32 and 33 on 32-bit builds. A LTC2983_SENSOR_NUM sentinel is added
> to the enum so that the bounds check uses >= LTC2983_SENSOR_NUM
> rather than hardcoding the last sensor type.
> 
> Tested on EVAL-ADT7604-AZ connected to Raspberry Pi 5 via SPI.
> 
> Signed-off-by: Liviu Stan <liviu.stan@analog.com>

The sashiko comment about the completion race looks real to me.
Can you take a look at that. Might be some odd reason why we can't
reinit_completion() before triggering the capture but that would
be very unusual.

Otherwise just two really small things I missed in earlier reviews.
If everything else was ready to go I'd have tweaked these whilst
applying but seems you'll be doing a v4 so over to you!

Jonathan

>  drivers/iio/temperature/ltc2983.c | 413 ++++++++++++++++++++++++++++--
>  1 file changed, 394 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/iio/temperature/ltc2983.c b/drivers/iio/temperature/ltc2983.c
> index 326f843f4271..e2ffeee026ee 100644
> --- a/drivers/iio/temperature/ltc2983.c
> +++ b/drivers/iio/temperature/ltc2983.c

> @@ -186,17 +188,44 @@ 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,
> +	LTC2983_SENSOR_NUM,

That's a terminating entry so no trailing comma.  It always has to be last.

>  };

>  static const struct spi_device_id ltc2983_id_table[] = {
> @@ -1707,6 +2080,7 @@ static const struct spi_device_id ltc2983_id_table[] = {
>  	{ "ltc2984", (kernel_ulong_t)&ltc2984_chip_info_data },
>  	{ "ltc2986", (kernel_ulong_t)&ltc2986_chip_info_data },
>  	{ "ltm2985", (kernel_ulong_t)&ltm2985_chip_info_data },
> +	{ "adt7604", (kernel_ulong_t)&adt7604_chip_info_data },

As below.

>  	{ }
>  };
>  MODULE_DEVICE_TABLE(spi, ltc2983_id_table);
> @@ -1716,6 +2090,7 @@ static const struct of_device_id ltc2983_of_match[] = {
>  	{ .compatible = "adi,ltc2984", .data = &ltc2984_chip_info_data },
>  	{ .compatible = "adi,ltc2986", .data = &ltc2986_chip_info_data },
>  	{ .compatible = "adi,ltm2985", .data = &ltm2985_chip_info_data },
> +	{ .compatible = "adi,adt7604", .data = &adt7604_chip_info_data },

Oops I missed this before. Alphabetical order. 

Jonathan

>  	{ }