From: marc.ferland@gmail.com
To: lars@metafoo.de
Cc: Michael.Hennerich@analog.com, jic23@kernel.org,
linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org,
Marc Ferland <marc.ferland@sonatest.com>
Subject: [PATCH v2] iio: dac: ad5592r: fix temperature channel scaling value
Date: Wed, 1 May 2024 11:05:54 -0400 [thread overview]
Message-ID: <20240501150554.1871390-1-marc.ferland@sonatest.com> (raw)
From: Marc Ferland <marc.ferland@sonatest.com>
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.
Signed-off-by: Marc Ferland <marc.ferland@sonatest.com>
---
Change in v2:
- Improve commit message as suggested by Jonathan.
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);
base-commit: 98369dccd2f8e16bf4c6621053af7aa4821dcf8e
--
2.34.1
next reply other threads:[~2024-05-01 15:06 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-01 15:05 marc.ferland [this message]
2024-05-06 14:35 ` [PATCH v2] iio: dac: ad5592r: fix temperature channel scaling value Jonathan Cameron
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