| Message ID | 20240730-iio-fix-scale-v1-1-6246638c8daa@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
| Series | iio: fix scale application in iio_convert_raw_to_processed_unlocked | expand |
On Tue, 30 Jul 2024 10:11:53 +0200 Matteo Martelli <matteomartelli3@gmail.com> wrote: > When the scale_type is IIO_VAL_INT_PLUS_MICRO or IIO_VAL_INT_PLUS_NANO > the scale passed as argument is only applied to the fractional part of > the value. Fix it by also multiplying the integer part by the scale > provided. > > Fixes: 48e44ce0f881 ("iio:inkern: Add function to read the processed value") > Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com> Ouch. I only vaguely recall the history of this, but I suspect that extra 'scale' was an after thought and we messed it up. Anyhow, applied to the fixes-togreg branch of iio.git and marked for stable. Jonathan > --- > I found out that after iio_hwmon switched to > iio_read_channel_processed_scale() to convert the power channel value > from milli-Watts to micro-Watts [1], lm-sensors started to show > unexpected values for the power channel of the pac1921 iio driver I was > testing. It looks the issue relies in the > iio_convert_raw_to_processed_unlocked() function that only applies the > given scale to the fractional part if the channel scale type is > IIO_VAL_INT_PLUS_MICRO or IIO_VAL_INT_PLUS_NANO. > > For example with a raw power value of 71, a power scale type of > IIO_VAL_INT_PLUS_NANO and power scale value of 9.775200000 (mW) the > processed power value would be ~694 mW but when scaled to uW by the > iio_hwmon calling iio_read_channel_processed_scale() with a scale of > 1000, the processed power would wrongly result to ~55678 uW (~55mW) = > 71*9 + 71*775200000*1000/1000000000. This because the scale of 1000 is > only applied to the fractional part of the power value. Instead it > should be 71*9*1000 + 71*775200000*1000/1000000000 = 694039 uW. > > [1]: https://lore.kernel.org/linux-hwmon/20240620212005.821805-1-sean.anderson@linux.dev/ > --- > drivers/iio/inkern.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c > index 9f484c94bc6e..151099be2863 100644 > --- a/drivers/iio/inkern.c > +++ b/drivers/iio/inkern.c > @@ -647,17 +647,17 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan, > break; > case IIO_VAL_INT_PLUS_MICRO: > if (scale_val2 < 0) > - *processed = -raw64 * scale_val; > + *processed = -raw64 * scale_val * scale; > else > - *processed = raw64 * scale_val; > + *processed = raw64 * scale_val * scale; > *processed += div_s64(raw64 * (s64)scale_val2 * scale, > 1000000LL); > break; > case IIO_VAL_INT_PLUS_NANO: > if (scale_val2 < 0) > - *processed = -raw64 * scale_val; > + *processed = -raw64 * scale_val * scale; > else > - *processed = raw64 * scale_val; > + *processed = raw64 * scale_val * scale; > *processed += div_s64(raw64 * (s64)scale_val2 * scale, > 1000000000LL); > break; > > --- > base-commit: 1ebab783647a9e3bf357002d5c4ff060c8474a0a > change-id: 20240729-iio-fix-scale-287b7630374e > > Best regards,
diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c index 9f484c94bc6e..151099be2863 100644 --- a/drivers/iio/inkern.c +++ b/drivers/iio/inkern.c @@ -647,17 +647,17 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan, break; case IIO_VAL_INT_PLUS_MICRO: if (scale_val2 < 0) - *processed = -raw64 * scale_val; + *processed = -raw64 * scale_val * scale; else - *processed = raw64 * scale_val; + *processed = raw64 * scale_val * scale; *processed += div_s64(raw64 * (s64)scale_val2 * scale, 1000000LL); break; case IIO_VAL_INT_PLUS_NANO: if (scale_val2 < 0) - *processed = -raw64 * scale_val; + *processed = -raw64 * scale_val * scale; else - *processed = raw64 * scale_val; + *processed = raw64 * scale_val * scale; *processed += div_s64(raw64 * (s64)scale_val2 * scale, 1000000000LL); break;
When the scale_type is IIO_VAL_INT_PLUS_MICRO or IIO_VAL_INT_PLUS_NANO the scale passed as argument is only applied to the fractional part of the value. Fix it by also multiplying the integer part by the scale provided. Fixes: 48e44ce0f881 ("iio:inkern: Add function to read the processed value") Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com> --- I found out that after iio_hwmon switched to iio_read_channel_processed_scale() to convert the power channel value from milli-Watts to micro-Watts [1], lm-sensors started to show unexpected values for the power channel of the pac1921 iio driver I was testing. It looks the issue relies in the iio_convert_raw_to_processed_unlocked() function that only applies the given scale to the fractional part if the channel scale type is IIO_VAL_INT_PLUS_MICRO or IIO_VAL_INT_PLUS_NANO. For example with a raw power value of 71, a power scale type of IIO_VAL_INT_PLUS_NANO and power scale value of 9.775200000 (mW) the processed power value would be ~694 mW but when scaled to uW by the iio_hwmon calling iio_read_channel_processed_scale() with a scale of 1000, the processed power would wrongly result to ~55678 uW (~55mW) = 71*9 + 71*775200000*1000/1000000000. This because the scale of 1000 is only applied to the fractional part of the power value. Instead it should be 71*9*1000 + 71*775200000*1000/1000000000 = 694039 uW. [1]: https://lore.kernel.org/linux-hwmon/20240620212005.821805-1-sean.anderson@linux.dev/ --- drivers/iio/inkern.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- base-commit: 1ebab783647a9e3bf357002d5c4ff060c8474a0a change-id: 20240729-iio-fix-scale-287b7630374e Best regards,