This is a note to let you know that I've just added the patch titled
iio: dac: ad5592r: fix temperature channel scaling value
to my char-misc git tree which can be found at git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git in the char-misc-linus branch.
The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)
The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.
If you have any questions about this process, please let me know.
From 279428df888319bf68f2686934897301a250bb84 Mon Sep 17 00:00:00 2001 From: Marc Ferland marc.ferland@sonatest.com Date: Wed, 1 May 2024 11:05:54 -0400 Subject: iio: dac: ad5592r: fix temperature channel scaling value
The scale value for the temperature channel is (assuming Vref=2.5 and the datasheet):
376.7897513
When calculating both val and val2 for the temperature scale we use (3767897513/25) and multiply it by Vref (here I assume 2500mV) to obtain:
2500 * (3767897513/25) ==> 376789751300
Finally we divide with remainder by 10^9 to get:
val = 376 val2 = 789751300
However, we return IIO_VAL_INT_PLUS_MICRO (should have been NANO) as the scale type. So when converting the raw temperature value to the 'processed' temperature value we will get (assuming raw=810, offset=-753):
processed = (raw + offset) * scale_val = (810 + -753) * 376 = 21432
processed += div((raw + offset) * scale_val2, 10^6) += div((810 + -753) * 789751300, 10^6) += 45015 ==> 66447 ==> 66.4 Celcius
instead of the expected 21.5 Celsius.
Fix this issue by changing IIO_VAL_INT_PLUS_MICRO to IIO_VAL_INT_PLUS_NANO.
Fixes: 56ca9db862bf ("iio: dac: Add support for the AD5592R/AD5593R ADCs/DACs") Signed-off-by: Marc Ferland marc.ferland@sonatest.com Link: https://lore.kernel.org/r/20240501150554.1871390-1-marc.ferland@sonatest.com Cc: Stable@vger.kernel.org Signed-off-by: Jonathan Cameron Jonathan.Cameron@huawei.com --- drivers/iio/dac/ad5592r-base.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/iio/dac/ad5592r-base.c b/drivers/iio/dac/ad5592r-base.c index 076bc9ecfb49..4763402dbcd6 100644 --- a/drivers/iio/dac/ad5592r-base.c +++ b/drivers/iio/dac/ad5592r-base.c @@ -415,7 +415,7 @@ static int ad5592r_read_raw(struct iio_dev *iio_dev, s64 tmp = *val * (3767897513LL / 25LL); *val = div_s64_rem(tmp, 1000000000LL, val2);
- return IIO_VAL_INT_PLUS_MICRO; + return IIO_VAL_INT_PLUS_NANO; }
mutex_lock(&st->lock);