[PATCH v2 2/2] hwmon: (scpi) Fix the scale of SCP sensor readings

[Punit Agrawal]

Carlo Caione <carlo at caione.org> writes:

> From: Carlo Caione <carlo at endlessm.com>
>
> The implementation details for SCPI seems to suggest that the sensor
> readings must be reported by SCP using a well defined scale
> (millidegree Celsius for temperature, millivolts for voltage,
> milliamperes for current, microwatts for power and microjoules for
> energy).
>
> This is also important for the interaction with other subsystems: for
> example both the thermal sub-system and the hwmon sysfs interface expect
> the temperature expressed in millidegree Celsius.
>
> Unfortunately since this behaviour is dependent on the firmware
> implementation there are cases where the sensor readings are reported
> using a different scale. For example in the Amlogic SoCs the
> temperature is reported in degree and not millidegree Celsius.
>
> To take into account this discrepancy and fixup the values reported by
> SCP a new DT property `scpi,sensors-scale' is introduced and used in
> this patch by the scpi-hwmon driver to convert the sensor readings to
> the expected scale.
>
> Signed-off-by: Carlo Caione <carlo at endlessm.com>
> ---
>  drivers/hwmon/scpi-hwmon.c | 34 ++++++++++++++++++++++++++++++++++
>  1 file changed, 34 insertions(+)
>
> diff --git a/drivers/hwmon/scpi-hwmon.c b/drivers/hwmon/scpi-hwmon.c
> index 094f948f99ff..b64fe7d10742 100644
> --- a/drivers/hwmon/scpi-hwmon.c
> +++ b/drivers/hwmon/scpi-hwmon.c
> @@ -23,6 +23,7 @@
>  #include <linux/thermal.h>
>  
>  struct sensor_data {
> +	unsigned int scale;
>  	struct scpi_sensor_info info;
>  	struct device_attribute dev_attr_input;
>  	struct device_attribute dev_attr_label;
> @@ -44,6 +45,22 @@ struct scpi_sensors {
>  	const struct attribute_group *groups[2];
>  };
>  
> +static const u32 scpi_scale[] = {
> +	[TEMPERATURE]	= 1000,		/* (millicelsius)	*/
> +	[VOLTAGE]	= 1000,		/* (millivolts)		*/
> +	[CURRENT]	= 1000,		/* (milliamperes)	*/
> +	[POWER]		= 1000000,	/* (microwatts)		*/
> +	[ENERGY]	= 1000000,	/* (microjoules)	*/
> +};
> +
> +void scpi_scale_reading(u64 *value, struct sensor_data *sensor)

This function is not intended for use outside this file. Please mark as
static.

> +{
> +	if (scpi_scale[sensor->info.class] != sensor->scale) {
> +		*value *= scpi_scale[sensor->info.class];
> +		do_div(*value, sensor->scale);
> +	}
> +}
> +
>  static int scpi_read_temp(void *dev, int *temp)
>  {
>  	struct scpi_thermal_zone *zone = dev;
> @@ -57,6 +74,8 @@ static int scpi_read_temp(void *dev, int *temp)
>  	if (ret)
>  		return ret;
>  
> +	scpi_scale_reading(&value, sensor);
> +
>  	*temp = value;
>  	return 0;
>  }
> @@ -77,6 +96,8 @@ scpi_show_sensor(struct device *dev, struct device_attribute *attr, char *buf)
>  	if (ret)
>  		return ret;
>  
> +	scpi_scale_reading(&value, sensor);
> +
>  	return sprintf(buf, "%llu\n", value);
>  }
>  
> @@ -97,6 +118,7 @@ static struct thermal_zone_of_device_ops scpi_sensor_ops = {
>  static int scpi_hwmon_probe(struct platform_device *pdev)
>  {
>  	u16 nr_sensors, i;
> +	u32 scale[] = { 1000, 1000, 1000, 1000000, 1000000 };
>  	int num_temp = 0, num_volt = 0, num_current = 0, num_power = 0;
>  	int num_energy = 0;
>  	struct scpi_ops *scpi_ops;
> @@ -131,6 +153,16 @@ static int scpi_hwmon_probe(struct platform_device *pdev)
>  
>  	scpi_sensors->scpi_ops = scpi_ops;
>  
> +	of_property_read_u32_array(dev->of_node, "scpi,sensors-scale",
> +				   scale, ARRAY_SIZE(scale));
> +
> +	for (i = 0; i < ARRAY_SIZE(scale); i++) {
> +		if (!scale[i]) {
> +			dev_err(dev, "%s: scale cannot be zero (%d)\n", __func__, i);
> +			return -EINVAL;
> +		}
> +	}
> +
>  	for (i = 0, idx = 0; i < nr_sensors; i++) {
>  		struct sensor_data *sensor = &scpi_sensors->data[idx];
>  
> @@ -178,6 +210,8 @@ static int scpi_hwmon_probe(struct platform_device *pdev)
>  			continue;
>  		}
>  
> +		sensor->scale = scale[sensor->info.class];
> +
>  		sensor->dev_attr_input.attr.mode = S_IRUGO;
>  		sensor->dev_attr_input.show = scpi_show_sensor;
>  		sensor->dev_attr_input.attr.name = sensor->input;

So with the function marked as static,

Acked-by: Punit Agrawal <punit.agrawal at arm.com>