linux-kernel - Re: [PATCH v2 2/2] thermal: thermal-generic-adc: add temperature sensor channel

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Message-ID: <CAPVz0n0uWEY+-evrfpci9-1c3icGyHfTHMbXi=P9Sv=Uh3AUaA@mail.gmail.com>
Date: Fri, 28 Feb 2025 15:22:00 +0200
From: Svyatoslav Ryhel <clamor95@...il.com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-pm@...r.kernel.org, Conor Dooley <conor+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org, 
	Zhang Rui <rui.zhang@...el.com>, Daniel Lezcano <daniel.lezcano@...aro.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Laxman Dewangan <ldewangan@...dia.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] thermal: thermal-generic-adc: add temperature
 sensor channel

пт, 28 лют. 2025 р. о 15:11 Lukasz Luba <lukasz.luba@....com> пише:
>
> Hi Svyatoslav,
>
> On 2/19/25 08:28, Svyatoslav Ryhel wrote:
> > Add IIO sensor channel along with existing thermal sensor cell. This
> > would benefit devices that use adc sensors to detect temperature and
> > need a custom conversion table.
> >
> > 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),
> > +     }
> > +};
> > +
> > +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;
> > +
> > +     ret = gadc_thermal_get_temp(gtinfo->tz_dev, temp);
> > +     if (ret < 0)
> > +             return ret;
> > +
> > +     *temp /= 1000;
> > +
> > +     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);
>
> I don't get the idea why we need iio device, while we already have the
> hwmon.
>

Idea behind this is to be able to convert adc iio channel into temp
iio channel without introducing a new sensor which will duplicate
behavior of existing one (by this I mean conversion table use). Not
all devices can or have to use hwmon and some may require iio channel
hooked up.

Real life example. I own a device (LG P985) which has a fuel gauge
that does not support battery thermal readings. Vendor provided a
dedicated adc sensor and one of its channels is used as thermal sensor
with device specific conversion table. Fuel gauge on the other hand
supports linking in a dedicated temp iio channel to get thermal
readings.

> Could you explain this a bit more, the cover letter also misses
> such justification and details.
>
> Regards,
> Lukasz