patch "iio: dac: ad5592r: fix temperature channel scaling value" added to char-misc-linus

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 <[email protected]>
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.

---
 drivers/iio/dac/ad5592r-base.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 076bc9ecfb49..4763402dbcd6 100644
@@ -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);

2.45.2