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[ 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: 48e44ce0f8 ("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.