linux-kernel - Re: [PATCH v2 3/4] iio: adc: ltc2497: add temperature sensor support

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Message-ID: <CAHp75VfM6WzNCT=ihN=wkaY0dQwjnJ0VLSyaGVbhCw4Lg-aXAQ@mail.gmail.com>
Date: Wed, 13 Aug 2025 19:14:16 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Yusuf Alper Bilgin <y.alperbilgin@...il.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, 
	Jonathan Cameron <jic23@...nel.org>, David Lechner <dlechner@...libre.com>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Liam Beguin <liambeguin@...il.com>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/4] iio: adc: ltc2497: add temperature sensor support

On Wed, Aug 13, 2025 at 6:54 PM Yusuf Alper Bilgin
<y.alperbilgin@...il.com> wrote:
>
> Support for reading the internal temperature sensor on LTC2495 and
> LTC2499 via a standard IIO temperature channel.

...

> +#define LTC2497_KELVIN_TO_CELCIUS      273

Drop it, see below why.

...

> +               *val = -LTC2497_KELVIN_TO_CELCIUS * ddata->chip_info->temp_scale_mV;

Can you use kelvin_to_celsius(0) from units.h instead?

> +               *val2 = ret / 1000;
> +
> +               return IIO_VAL_FRACTIONAL;

...

> +#define LTC2497_T_CHAN {                                                                       \

It's better to locate { on the new line.

> +       .type = IIO_TEMP,                                                                       \
> +       .channel = 0,                                                                           \
> +       .address = (LTC2497_ENABLE_TEMPERATURE_CONV),                                           \
> +       .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),                                           \
> +       .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),       \
> +}

...

> +       LTC2497_CHANNELS,

Seems like a terminator, so add _MAX in the middle and remove the
trailing comma.

...


> +static const struct iio_chan_spec ltc2497core_channel_with_temperature[] = {
> +       LTC2497_CHANNELS,
> +       LTC2497_T_CHAN,

(Same as above may be applied to _T_CHAN, but I haven't seen the enum
to be sure)

>  };

...

>  struct ltc2497_chip_info {
> -       u32 resolution;
>         const char *name;
> +       u32 resolution;

Perhaps above deserves a separate change (with the `pahole` summary),
but I don't care as it's a little change here. Leave this to Jonathan
to decide.

> +       /*
> +        * Represents the datasheet constant from the temperature formula:
> +        * T_Kelvin = (DATAOUT * Vref) / temp_scale, where Vref is in Volts.
> +        *
> +        * To allow the driver to use Vref in millivolts for the calculation
> +        * and also to avoid floating points, this stored value represents the
> +        * datasheet constant scaled by 1000.
> +        */
> +       u32 temp_scale_mV;
> +       bool has_temp_channel;
>  };

-- 
With Best Regards,
Andy Shevchenko