linux-kernel - Re: [PATCH v3] hwmon: (scpi-hwmon) shows the negative temperature properly

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Date:   Fri, 4 Jun 2021 04:09:10 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Riwen Lu <luriwen@...inos.cn>
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xin Chen <chenxin@...inos.cn>
Subject: Re: [PATCH v3] hwmon: (scpi-hwmon) shows the negative temperature
 properly

On Fri, Jun 04, 2021 at 11:09:59AM +0800, Riwen Lu wrote:
> The scpi hwmon shows the sub-zero temperature in an unsigned integer,
> which would confuse the users when the machine works in low temperature
> environment. This shows the sub-zero temperature in an signed value and
> users can get it properly from sensors.
> 
> Signed-off-by: Riwen Lu <luriwen@...inos.cn>
> Tested-by: Xin Chen <chenxin@...inos.cn>

Applied.

Thanks,
Guenter

> ---
> Changes since v1:
> - Add judgment for sensor->info.class. If it is TEMPERATURE situation,
>   return the sensor value as a signed value, otherwise return it as a
>   unsigned value.
> 
> Changes since v2:
> - Add a typecast u64 to s64 when it is a temperature value.
> - Add a comment ahead of the if statement.
> - Remove the unnecessary 'else' statement.
> ---
>  drivers/hwmon/scpi-hwmon.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/hwmon/scpi-hwmon.c b/drivers/hwmon/scpi-hwmon.c
> index 25aac40f2764..919877970ae3 100644
> --- a/drivers/hwmon/scpi-hwmon.c
> +++ b/drivers/hwmon/scpi-hwmon.c
> @@ -99,6 +99,15 @@ scpi_show_sensor(struct device *dev, struct device_attribute *attr, char *buf)
>  
>  	scpi_scale_reading(&value, sensor);
>  
> +	/*
> +	 * Temperature sensor values are treated as signed values based on
> +	 * observation even though that is not explicitly specified, and
> +	 * because an unsigned u64 temperature does not really make practical
> +	 * sense especially when the temperature is below zero degrees Celsius.
> +	 */
> +	if (sensor->info.class == TEMPERATURE)
> +		return sprintf(buf, "%lld\n", (s64)value);
> +
>  	return sprintf(buf, "%llu\n", value);
>  }
>