linux-kernel - Re: [PATCH v2 14/29] ASoC: tas2770: expose die temp to hwmon

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Message-ID: <CAHgNfTzfK4HnYs+LDH7kcR+pZqSxT9YBZYQ=c+Mcpva4Vx=D_w@mail.gmail.com>
Date: Fri, 21 Feb 2025 21:31:08 +1000
From: James Calligeros <jcalligeros99@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, Shenghao Ding <shenghao-ding@...com>, 
	Kevin Lu <kevin-lu@...com>, Baojun Xu <baojun.xu@...com>, Dan Murphy <dmurphy@...com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Shi Fu <shifu0704@...ndersoft.com>, Jean Delvare <jdelvare@...e.com>, 
	Alyssa Rosenzweig <alyssa@...enzweig.io>, Martin Povišer <povik+lin@...ebit.org>, 
	Hector Martin <marcan@...can.st>, linux-sound@...r.kernel.org, 
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	asahi@...ts.linux.dev, linux-hwmon@...r.kernel.org
Subject: Re: [PATCH v2 14/29] ASoC: tas2770: expose die temp to hwmon

On Wed, Feb 19, 2025 at 1:20 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 2/18/25 00:35, James Calligeros wrote:
> > +static int tas2770_hwmon_read(struct device *dev,
> > +                           enum hwmon_sensor_types type,
> > +                           u32 attr, int channel, long *val)
> > +{
> > +     struct tas2770_priv *tas2770 = i2c_get_clientdata(to_i2c_client(dev));
> > +     int ret;
> > +
> > +     switch (attr) {
> > +     case hwmon_temp_input:
> > +             ret = tas2770_read_die_temp(tas2770, (int *)val);
>
> Type casting a pointer like this is never a good idea. This only works
> if sizeof(int) == sizeof(long).

I will rework this when dropping the die temp sysfs interface. This
was mostly so that
I didn't have to change any of the code there, but since we're going
to drop that
anyway it's redundant.

> > +             if (!ret)
> > +                     *val *= 1000;
>
> The calculations in the previous patch suggest that this is wrong.
>
> Either case, this is redundant. The temperature is already displayed
> as device specific sysfs attribute. Displaying it twice does not make sense.
> I would suggest to either drop the sysfs attribute in the previous patch
> or to drop this patch.

The calculation in the datasheet yields the temperature in degrees Celsius.
hwmon consumers expect temperatures in "millidegrees" Celsius as per the
sysfs interface documentation[1]. Regardless, as above I will likely rework this
when dropping the die temp sysfs interface so that things are a little
more logical.

Regards,
James

[1] https://www.kernel.org/doc/Documentation/hwmon/sysfs-interface