Patch "iio: dac: ad5592r: fix temperature channel scaling value" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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 the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     iio-dac-ad5592r-fix-temperature-channel-scaling-valu.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 3594da85e46301f66c2496daa2462b6e80480277
Author: Marc Ferland <marc.ferland@xxxxxxxxxxxx>
Date:   Wed May 1 11:05:54 2024 -0400

    iio: dac: ad5592r: fix temperature channel scaling value
    
    [ Upstream commit 279428df888319bf68f2686934897301a250bb84 ]
    
    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@xxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240501150554.1871390-1-marc.ferland@xxxxxxxxxxxx
    Cc: <Stable@xxxxxxxxxxxxxxx>
    Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/iio/dac/ad5592r-base.c b/drivers/iio/dac/ad5592r-base.c
index 5c242479bb811..75025be02dd29 100644
--- a/drivers/iio/dac/ad5592r-base.c
+++ b/drivers/iio/dac/ad5592r-base.c
@@ -414,7 +414,7 @@ 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);