6.17-stable review patch. If anyone has any objections, please let me know.
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From: Hans de Goede hansg@kernel.org
[ Upstream commit 0f85406bf830eb8747dd555ab53c9d97ee4af293 ]
There is an issue with the handling of negative channel scales in iio_convert_raw_to_processed_unlocked() when the channel-scale is of the IIO_VAL_INT_PLUS_[MICRO|NANO] type:
Things work for channel-scale values > -1.0 and < 0.0 because of the use of signed values in:
*processed += div_s64(raw64 * (s64)scale_val2 * scale, 1000000LL);
Things will break however for scale values < -1.0. Lets for example say that raw = 2, (caller-provided)scale = 10 and (channel)scale_val = -1.5.
The result should then be 2 * 10 * -1.5 = -30.
channel-scale = -1.5 means scale_val = -1 and scale_val2 = 500000, now lets see what gets stored in processed:
1. *processed = raw64 * scale_val * scale; 2. *processed += raw64 * scale_val2 * scale / 1000000LL;
1. Sets processed to 2 * -1 * 10 = -20 2. Adds 2 * 500000 * 10 / 1000000 = 10 to processed
And the end result is processed = -20 + 10 = -10, which is not correct.
Fix this by always using the abs value of both scale_val and scale_val2 and if either is negative multiply the end-result by -1.
Note there seems to be an unwritten rule about negative IIO_VAL_INT_PLUS_[MICRO|NANO] values that:
i. values > -1.0 and < 0.0 are written as val=0 val2=-xxx ii. values <= -1.0 are written as val=-xxx val2=xxx
But iio_format_value() will also correctly display a third option:
iii. values <= -1.0 written as val=-xxx val2=-xxx
Since iio_format_value() uses abs(val) when val2 < 0.
This fix also makes iio_convert_raw_to_processed() properly handle channel-scales using this third option.
Fixes: 48e44ce0f881 ("iio:inkern: Add function to read the processed value") Cc: Matteo Martelli matteomartelli3@gmail.com Reviewed-by: Andy Shevchenko andy@kernel.org Signed-off-by: Hans de Goede hansg@kernel.org Link: https://patch.msgid.link/20250831104825.15097-2-hansg@kernel.org Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/iio/inkern.c | 28 ++++++++++++++-------------- 1 file changed, 14 insertions(+), 14 deletions(-)
diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c index c174ebb7d5e6d..d36a80a7b8a93 100644 --- a/drivers/iio/inkern.c +++ b/drivers/iio/inkern.c @@ -11,6 +11,7 @@ #include <linux/mutex.h> #include <linux/property.h> #include <linux/slab.h> +#include <linux/units.h>
#include <linux/iio/iio.h> #include <linux/iio/iio-opaque.h> @@ -604,7 +605,7 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan, { int scale_type, scale_val, scale_val2; int offset_type, offset_val, offset_val2; - s64 raw64 = raw; + s64 denominator, raw64 = raw;
offset_type = iio_channel_read(chan, &offset_val, &offset_val2, IIO_CHAN_INFO_OFFSET); @@ -648,20 +649,19 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan, *processed = raw64 * scale_val * scale; break; case IIO_VAL_INT_PLUS_MICRO: - if (scale_val2 < 0) - *processed = -raw64 * scale_val * scale; - else - *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 * scale; - else - *processed = raw64 * scale_val * scale; - *processed += div_s64(raw64 * (s64)scale_val2 * scale, - 1000000000LL); + switch (scale_type) { + case IIO_VAL_INT_PLUS_MICRO: + denominator = MICRO; + break; + case IIO_VAL_INT_PLUS_NANO: + denominator = NANO; + break; + } + *processed = raw64 * scale * abs(scale_val); + *processed += div_s64(raw64 * scale * abs(scale_val2), denominator); + if (scale_val < 0 || scale_val2 < 0) + *processed *= -1; break; case IIO_VAL_FRACTIONAL: *processed = div_s64(raw64 * (s64)scale_val * scale,