linux-kernel - Re: [PATCH v2 3/3] hwmon: scmi: Scale values to target desired HWMON units

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Date:   Tue, 7 May 2019 14:14:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Jean Delvare <jdelvare@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        "open list:HARDWARE MONITORING" <linux-hwmon@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 3/3] hwmon: scmi: Scale values to target desired HWMON
 units

On Tue, May 07, 2019 at 12:35:04PM -0700, Florian Fainelli wrote:
> If the SCMI firmware implementation is reporting values in a scale that
> is different from the HWMON units, we need to scale up or down the value
> according to how far appart they are.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  drivers/hwmon/scmi-hwmon.c | 30 +++++++++++++++++++++++++++++-
>  1 file changed, 29 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/scmi-hwmon.c b/drivers/hwmon/scmi-hwmon.c
> index a80183a488c5..5c244053efc8 100644
> --- a/drivers/hwmon/scmi-hwmon.c
> +++ b/drivers/hwmon/scmi-hwmon.c
> @@ -18,6 +18,34 @@ struct scmi_sensors {
>  	const struct scmi_sensor_info **info[hwmon_max];
>  };
>  
> +static u64 scmi_hwmon_scale(const struct scmi_sensor_info *sensor, u64 value)
> +{
> +	s8 scale = sensor->scale;
> +	unsigned long long f;

do_div() takes either an uint32 or an unsigned long as second parameter,
so this doesn't really help. If you want to be able to handle scales
outside the 32-bit range, you would have to use u64 and div64_u64().

Guenter

> +
> +	switch (sensor->type) {
> +	case TEMPERATURE_C:
> +	case VOLTAGE:
> +	case CURRENT:
> +		scale += 3;
> +		break;
> +	case POWER:
> +	case ENERGY:
> +		scale += 6;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	__pow10(abs(scale), f);
> +	if (scale > 0)
> +		value *= f;
> +	else
> +		do_div(value, f);
> +
> +        return value;
> +}
> +
>  static int scmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  			   u32 attr, int channel, long *val)
>  {
> @@ -30,7 +58,7 @@ static int scmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
>  	sensor = *(scmi_sensors->info[type] + channel);
>  	ret = h->sensor_ops->reading_get(h, sensor->id, false, &value);
>  	if (!ret)
> -		*val = value;
> +		*val = scmi_hwmon_scale(sensor, value);
>  
>  	return ret;
>  }
> -- 
> 2.17.1
>