Re: [PATCH v4 2/2] thermal: thermal-generic-adc: add temperature sensor channel

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 5 Apr 2025 18:23:25 +0300
Svyatoslav Ryhel <clamor95@gmail.com> wrote:

> пн, 10 бер. 2025 р. о 09:57 Svyatoslav Ryhel <clamor95@gmail.com> пише:
> >
> > 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.
> >
> > The temperature data, while technically a product of conversion and thus
> > categorized as IIO_CHAN_INFO_PROCESSED, maintains its unscaled state
> > (milli-degree). To account for this, IIO_CHAN_INFO_RAW is used along with
> > IIO_CHAN_INFO_SCALE to provide different degrees of accuracy.

You've lost me in this description.  The base units of an IIO temperature channel
are milli-degrees so if the scaling is already right for that you would
be fine using a IIO_CHAN_INFO_PROCESSED channel.

A few other minor things inline.

> >
> > Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
> > ---
> >  drivers/thermal/thermal-generic-adc.c | 62 ++++++++++++++++++++++++++-
> >  1 file changed, 61 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/thermal/thermal-generic-adc.c b/drivers/thermal/thermal-generic-adc.c
> > index ee3d0aa31406..7dcc2e1168a4 100644
> > --- a/drivers/thermal/thermal-generic-adc.c
> > +++ b/drivers/thermal/thermal-generic-adc.c
> > @@ -7,6 +7,7 @@
> >   * Author: Laxman Dewangan <ldewangan@nvidia.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 +74,65 @@ 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[] = {
Even though there is only one. If it is an array use channels.

or stop it being an array and just take a pointer to a single channel
instance.

> > +       {
> > +               .type = IIO_TEMP,
> > +               .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
> > +                                     BIT(IIO_CHAN_INFO_SCALE),
> > +       }
> > +};
> > +
> > +static int gadc_thermal_read_raw(struct iio_dev *indio_dev,
> > +                                struct iio_chan_spec const *chan,
> > +                                int *val, int *val2, long mask)
> > +{
> > +       struct gadc_thermal_info *gtinfo = iio_priv(indio_dev);
> > +       int ret;
> > +
> > +       switch (mask) {
> > +       case IIO_CHAN_INFO_RAW:
> > +               ret = gadc_thermal_get_temp(gtinfo->tz_dev, val);
> > +               if (ret)
> > +                       return ret;
> > +
> > +               return IIO_VAL_INT;
> > +
> > +       case IIO_CHAN_INFO_SCALE:
> > +               /* scale to a degree centigrade */

As above.  See Documentation/ABI/testing/sysfs-bus-iio
entries from temperature. Scaling of a temperature channel is milli-degrees

This is a bit of a historical artefact. Way back at the start of IIO
when we had relatively few channel types, where possible I matched the
scaling to hwmon.  With hindsight that made things a bit inconsistent
but we are stuck with it as ABI :(

Jonathan

> > +               *val = 1;
> > +               *val2 = 1000;
> > +               return IIO_VAL_FRACTIONAL;
> > +
> > +       default:
> > +               return -EINVAL;
> > +       }
> > +}
> > +
> > +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));

sizeof(*gtinfo) probably slightly better.

> > +
> > +       indio_dev->name = dev_name(dev);

What does this end up as?  The convention in IIO is to name after
a part number.  If you have duplicates this isn't how you tell them
apart.  So I'd kind of expect thermal-generic-temp or
something like that.

> > +       indio_dev->info = &gadc_thermal_iio_info;
> > +       indio_dev->modes = INDIO_DIRECT_MODE;
> > +       indio_dev->channels = gadc_thermal_iio_channel;
As above, I'd stop that being an array and use
	indio_dev->channels = &gadc_thermal_iio_chanel;
	indio_dev->channels = 1;

Unless you think maybe we will get more channels in future, in which case
just rename it channels (which happens to have one element this time)

> > +       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 +213,7 @@ 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[] = {
> > --
> > 2.43.0
> >  
> 
> Added Jonathan Cameron and linux-iio@vger.kernel.org to list.
> 
> Jonathan, this is newer version of the thermal-generic-adc you have
> reviewed recently with channels adjusted like proposed in v3.