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SubjectRe: [PATCH 2/2] hwmon: scmi: Scale values to target desired HWMON units
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Hi Florian,

On 5/6/19 3:41 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@gmail.com>
> ---
> drivers/hwmon/scmi-hwmon.c | 55 +++++++++++++++++++++++++++++++-------
> 1 file changed, 46 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/hwmon/scmi-hwmon.c b/drivers/hwmon/scmi-hwmon.c
> index a80183a488c5..e9913509cb88 100644
> --- a/drivers/hwmon/scmi-hwmon.c
> +++ b/drivers/hwmon/scmi-hwmon.c
> @@ -18,6 +18,51 @@ struct scmi_sensors {
> const struct scmi_sensor_info **info[hwmon_max];
> };
>
> +static enum hwmon_sensor_types scmi_types[] = {
> + [TEMPERATURE_C] = hwmon_temp,
> + [VOLTAGE] = hwmon_in,
> + [CURRENT] = hwmon_curr,
> + [POWER] = hwmon_power,
> + [ENERGY] = hwmon_energy,
> +};
> +
> +static u64 scmi_hwmon_scale(const struct scmi_sensor_info *sensor, u64 value)
> +{
> + u64 scaled_value = value;

I don't think that variable is necessary.

> + s8 desired_scale;

Just scale ? Also, you could assign scale here directly, and subtract
the offset below. Then "n" would not be necessary.
Such as
s8 scale = sensor->scale; // assuming scale is s8
...
case CURRENT:
scale += 3;
...

That would also be less confusing, since it would avoid the double
negation.

> + int n, p;

> +
> + switch (sensor->type) {
> + case TEMPERATURE_C:
> + case VOLTAGE:
> + case CURRENT:
> + /* fall through */
Unnecessary comment

> + desired_scale = -3;
> + break;
> + case POWER:
> + case ENERGY:
> + /* fall through */
Unnecessary comment.

> + desired_scale = -6;
> + break;
> + default:
> + return scaled_value;

Here we presumably want a scale of 0. However, if the scale passed
from SCMI is, say, -5 or +5, we return the original (unadjusted)
value. Seems to me we would still want to adjust the value to match
hwmon expectations. Am I missing something ?

> + }
> +
> + n = (s8)sensor->scale - desired_scale;
> + if (n == 0)

Indentation seems off here.

> + return scaled_value;
> +
> + for (p = 0; p < abs(n); p++) {
> + /* Need to scale up from sensor to HWMON */
> + if (n > 0)
> + scaled_value *= 10;
> + else
> + do_div(scaled_value, 10);
> + }

Something like

factor = pow10(abs(scale));
if (scale > 0)
value *= factor;
else
do_div(value, factor);

would avoid the repeated abs() and do_div(). Unfortunately there is
no pow10() helper, so you would have to write that. Still, I think
that would be much more efficient.

Thanks,
Guenter

> +
> + return scaled_value;
> +}
> +
> static int scmi_hwmon_read(struct device *dev, enum hwmon_sensor_types type,
> u32 attr, int channel, long *val)
> {
> @@ -30,7 +75,7 @@ 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;
> }
> @@ -91,14 +136,6 @@ static int scmi_hwmon_add_chan_info(struct hwmon_channel_info *scmi_hwmon_chan,
> return 0;
> }
>
> -static enum hwmon_sensor_types scmi_types[] = {
> - [TEMPERATURE_C] = hwmon_temp,
> - [VOLTAGE] = hwmon_in,
> - [CURRENT] = hwmon_curr,
> - [POWER] = hwmon_power,
> - [ENERGY] = hwmon_energy,
> -};
> -
> static u32 hwmon_attributes[] = {
> [hwmon_chip] = HWMON_C_REGISTER_TZ,
> [hwmon_temp] = HWMON_T_INPUT | HWMON_T_LABEL,
>

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