[v4,2/2] hwmon: (scpi) Fix the scale of SCP sensor readings

[Guenter Roeck]

On Tue, May 30, 2017 at 11:05:07AM +0200, Carlo Caione wrote:
> 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 compatible 'amlogic,meson-gxbb-scpi-sensors' 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>
> Acked-by: Sudeep Holla <sudeep.holla at arm.com>

Applied to hwmon-next. If the dt property needs to be updated, we can do
that later.

Thanks,
Guenter

> ---
>  drivers/hwmon/scpi-hwmon.c | 54 ++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 48 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/hwmon/scpi-hwmon.c b/drivers/hwmon/scpi-hwmon.c
> index 094f948..a586480 100644
> --- a/drivers/hwmon/scpi-hwmon.c
> +++ b/drivers/hwmon/scpi-hwmon.c
> @@ -16,6 +16,7 @@
>  
>  #include <linux/hwmon.h>
>  #include <linux/module.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  #include <linux/scpi_protocol.h>
>  #include <linux/slab.h>
> @@ -23,6 +24,7 @@
>  #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 +46,30 @@ struct scpi_sensors {
>  	const struct attribute_group *groups[2];
>  };
>  
> +static const u32 gxbb_scpi_scale[] = {
> +	[TEMPERATURE]	= 1,		/* (celsius)		*/
> +	[VOLTAGE]	= 1000,		/* (millivolts)		*/
> +	[CURRENT]	= 1000,		/* (milliamperes)	*/
> +	[POWER]		= 1000000,	/* (microwatts)		*/
> +	[ENERGY]	= 1000000,	/* (microjoules)	*/
> +};
> +
> +static const u32 scpi_scale[] = {
> +	[TEMPERATURE]	= 1000,		/* (millicelsius)	*/
> +	[VOLTAGE]	= 1000,		/* (millivolts)		*/
> +	[CURRENT]	= 1000,		/* (milliamperes)	*/
> +	[POWER]		= 1000000,	/* (microwatts)		*/
> +	[ENERGY]	= 1000000,	/* (microjoules)	*/
> +};
> +
> +static void scpi_scale_reading(u64 *value, struct sensor_data *sensor)
> +{
> +	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 +83,8 @@ static int scpi_read_temp(void *dev, int *temp)
>  	if (ret)
>  		return ret;
>  
> +	scpi_scale_reading(&value, sensor);
> +
>  	*temp = value;
>  	return 0;
>  }
> @@ -77,6 +105,8 @@ 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);
>  }
>  
> @@ -94,14 +124,23 @@ static struct thermal_zone_of_device_ops scpi_sensor_ops = {
>  	.get_temp = scpi_read_temp,
>  };
>  
> +static const struct of_device_id scpi_of_match[] = {
> +	{.compatible = "arm,scpi-sensors", .data = &scpi_scale},
> +	{.compatible = "amlogic,meson-gxbb-scpi-sensors", .data = &gxbb_scpi_scale},
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, scpi_of_match);
> +
>  static int scpi_hwmon_probe(struct platform_device *pdev)
>  {
>  	u16 nr_sensors, i;
> +	const u32 *scale;
>  	int num_temp = 0, num_volt = 0, num_current = 0, num_power = 0;
>  	int num_energy = 0;
>  	struct scpi_ops *scpi_ops;
>  	struct device *hwdev, *dev = &pdev->dev;
>  	struct scpi_sensors *scpi_sensors;
> +	const struct of_device_id *of_id;
>  	int idx, ret;
>  
>  	scpi_ops = get_scpi_ops();
> @@ -131,6 +170,13 @@ static int scpi_hwmon_probe(struct platform_device *pdev)
>  
>  	scpi_sensors->scpi_ops = scpi_ops;
>  
> +	of_id = of_match_device(scpi_of_match, &pdev->dev);
> +	if (!of_id) {
> +		dev_err(&pdev->dev, "Unable to initialize scpi-hwmon data\n");
> +		return -ENODEV;
> +	}
> +	scale = of_id->data;
> +
>  	for (i = 0, idx = 0; i < nr_sensors; i++) {
>  		struct sensor_data *sensor = &scpi_sensors->data[idx];
>  
> @@ -178,6 +224,8 @@ 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;
> @@ -247,12 +295,6 @@ static int scpi_hwmon_probe(struct platform_device *pdev)
>  	return 0;
>  }
>  
> -static const struct of_device_id scpi_of_match[] = {
> -	{.compatible = "arm,scpi-sensors"},
> -	{},
> -};
> -MODULE_DEVICE_TABLE(of, scpi_of_match);
> -
>  static struct platform_driver scpi_hwmon_platdrv = {
>  	.driver = {
>  		.name	= "scpi-hwmon",