linux-kernel - Re: [PATCH v3 2/2] hwmon: scmi: Scale values to target desired HWMON units

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Date:   Tue, 7 May 2019 16:41:54 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Florian Fainelli <f.fainelli@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     bcm-kernel-feedback-list@...adcom.com,
        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>
Subject: Re: [PATCH v3 2/2] hwmon: scmi: Scale values to target desired HWMON
 units

On 5/7/19 4:09 PM, 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 | 43 +++++++++++++++++++++++++++++++++++++-
>   1 file changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwmon/scmi-hwmon.c b/drivers/hwmon/scmi-hwmon.c
> index a80183a488c5..7820854e5954 100644
> --- a/drivers/hwmon/scmi-hwmon.c
> +++ b/drivers/hwmon/scmi-hwmon.c
> @@ -18,6 +18,47 @@ struct scmi_sensors {
>   	const struct scmi_sensor_info **info[hwmon_max];
>   };
>   
> +static inline u64 __pow10(u8 x)
> +{
> +	u64 r = 1;
> +
> +	if (unlikely(x > 18))
> +		return r;
> +

Strictly speaking that would be 19 (10^19=0x8AC7230489E80000),
and I am not sure if returning 1 in that case is such a good idea.
If you really want to handle over/underflow situations, it should
be in the calling code.

Thanks,
Guenter

> +	while (x--)
> +		r *= 10;
> +
> +	return r;
> +}
> +
> +static u64 scmi_hwmon_scale(const struct scmi_sensor_info *sensor, u64 value)
> +{
> +	s8 scale = sensor->scale;
> +	u64 f;
> +
> +	switch (sensor->type) {
> +	case TEMPERATURE_C:
> +	case VOLTAGE:
> +	case CURRENT:
> +		scale += 3;
> +		break;
> +	case POWER:
> +	case ENERGY:
> +		scale += 6;
> +		break;
> +	default:
> +		break;
> +	}
> +
> +	f = __pow10(abs(scale));
> +	if (scale > 0)
> +		value *= f;
> +	else
> +		value = div64_u64(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 +71,7 @@ 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;
>   }
>