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

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Message-ID: <4993899.31r3eYUQgx@setsuna>
Date: Sat, 22 Feb 2025 10:16:57 +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 Saturday, 22 February 2025 1:03:38 am Australian Eastern Standard Time 
Guenter Roeck wrote:
> On 2/21/25 03:31, James Calligeros wrote:
> > 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
> Yes, I am well aware of that.
> 
> > when dropping the die temp sysfs interface so that things are a little
> > more logical.
> 
> Unless I really misread the code, tas2770_read_die_temp() doesn't return
> the temperature in degrees C.
> 
> Guenter

My mistake. We return an intermediate value that is then manipulated in
die_temp_show() to yield degrees. I will clean this up for the next submission
since we will no longer require the sysfs interface at all. Apologies for the
confusion.

Regards,
James