linux-kernel - Re: [PATCH v3 2/2] thermal: thermal-generic-adc: add temperature sensor channel

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Message-ID: <3bc7c5a5-8fe7-4c4b-a80e-23522922debb@arm.com>
Date: Wed, 5 Mar 2025 09:52:15 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Svyatoslav Ryhel <clamor95@...il.com>
Cc: linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
 Laxman Dewangan <ldewangan@...dia.com>, Conor Dooley <conor+dt@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH v3 2/2] thermal: thermal-generic-adc: add temperature
 sensor channel



On 3/3/25 12:21, Svyatoslav Ryhel wrote:
> To avoid duplicating sensor functionality and conversion tables, this design
> allows converting an ADC IIO channel's output directly into a temperature IIO
> channel. This is particularly useful for devices where hwmon isn't suitable
> or where temperature data must be accessible through IIO.
> 
> One such device is, for example, the MAX17040 fuel gauge.
> 
> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> ---
>   drivers/thermal/thermal-generic-adc.c | 54 ++++++++++++++++++++++++++-
>   1 file changed, 53 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
> index ee3d0aa31406..a8f3b965b39b 100644
> --- a/drivers/thermal/thermal-generic-adc.c
> +++ b/drivers/thermal/thermal-generic-adc.c
> @@ -7,6 +7,7 @@
>    * Author: Laxman Dewangan <ldewangan@...dia.com>
>    */
>   #include <linux/iio/consumer.h>
> +#include <linux/iio/iio.h>
>   #include <linux/kernel.h>
>   #include <linux/module.h>
>   #include <linux/platform_device.h>
> @@ -73,6 +74,57 @@ static const struct thermal_zone_device_ops gadc_thermal_ops = {
>   	.get_temp = gadc_thermal_get_temp,
>   };
>   
> +static const struct iio_chan_spec gadc_thermal_iio_channel[] = {
> +	{
> +		.type = IIO_TEMP,
> +		.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),

I would add the IIO_CHAN_INFO_SCALE and say it's in milli-degrees.

> +	}
> +};
> +
> +static int gadc_thermal_read_raw(struct iio_dev *indio_dev,
> +				 struct iio_chan_spec const *chan,
> +				 int *temp, int *val2, long mask)
> +{
> +	struct gadc_thermal_info *gtinfo = iio_priv(indio_dev);
> +	int ret;
> +
> +	if (mask != IIO_CHAN_INFO_PROCESSED)
> +		return -EINVAL;

Therefore, here it would need to handle such case as well, when
a client is asking about scale.

> +
> +	ret = gadc_thermal_get_temp(gtinfo->tz_dev, temp);
> +	if (ret < 0)
> +		return ret;
> +
> +	*temp /= 1000;

IMO we shouldn't cut the precision if it's provided.
The user of this would know what to do with the value (when
the proper information about scale is also available).

> +
> +	return IIO_VAL_INT;
> +}
> +
> +static const struct iio_info gadc_thermal_iio_info = {
> +	.read_raw = gadc_thermal_read_raw,
> +};
> +
> +static int gadc_iio_register(struct device *dev, struct gadc_thermal_info *gti)
> +{
> +	struct gadc_thermal_info *gtinfo;
> +	struct iio_dev *indio_dev;
> +
> +	indio_dev = devm_iio_device_alloc(dev, sizeof(struct gadc_thermal_info));
> +	if (!indio_dev)
> +		return -ENOMEM;
> +
> +	gtinfo = iio_priv(indio_dev);
> +	memcpy(gtinfo, gti, sizeof(struct gadc_thermal_info));
> +
> +	indio_dev->name = dev_name(dev);
> +	indio_dev->info = &gadc_thermal_iio_info;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = gadc_thermal_iio_channel;
> +	indio_dev->num_channels = ARRAY_SIZE(gadc_thermal_iio_channel);
> +
> +	return devm_iio_device_register(dev, indio_dev);
> +}
> +
>   static int gadc_thermal_read_linear_lookup_table(struct device *dev,
>   						 struct gadc_thermal_info *gti)
>   {
> @@ -153,7 +205,7 @@ static int gadc_thermal_probe(struct platform_device *pdev)
>   
>   	devm_thermal_add_hwmon_sysfs(dev, gti->tz_dev);
>   
> -	return 0;
> +	return gadc_iio_register(&pdev->dev, gti);
>   }
>   
>   static const struct of_device_id of_adc_thermal_match[] = {