[PATCH 3/4] ASoC: tas2770: Fix order of operations for temperature calculation

[James Calligeros]

The order of operations to derive the temperature from the temp
register values was wrong, since 1000 / 16 is not an integer. This
resulted in the calculated temperature value deviating from the
value represented by the registers slightly, which was most obvious
when the registers were zeroed (-92.265 *C vs the expected -93.000 *C).

Scale the reading before dividing the whole thing by 16 to correct
this.

Fixes: ff73e2780169 ("ASoC: tas2770: expose die temp to hwmon")
Signed-off-by: James Calligeros <jcalligeros99@xxxxxxxxx>
---
 sound/soc/codecs/tas2770.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sound/soc/codecs/tas2770.c b/sound/soc/codecs/tas2770.c
index d4d7d056141b..50501bcbe916 100644
--- a/sound/soc/codecs/tas2770.c
+++ b/sound/soc/codecs/tas2770.c
@@ -624,7 +624,7 @@ static int tas2770_read_die_temp(struct tas2770_priv *tas2770, long *result)
 	/*
 	 * As per datasheet: divide register by 16 and subtract 93 to get
 	 * degrees Celsius. hwmon requires millidegrees. Let's avoid rounding
-	 * errors by subtracting 93 * 16 then multiplying by 1000 / 16.
+	 * errors by subtracting 93 * 16 and scaling before dividing.
 	 *
 	 * NOTE: The ADC registers are initialised to 0 on reset. This means
 	 * that the temperature will read -93 *C until the chip is brought out
@@ -633,7 +633,7 @@ static int tas2770_read_die_temp(struct tas2770_priv *tas2770, long *result)
 	 * value read back from its registers will be the last value sampled
 	 * before entering software shutdown.
 	 */
-	*result = (reading - (93 * 16)) * (1000 / 16);
+	*result = (reading - (93 * 16)) * 1000 / 16;
 	return 0;
 }
 

-- 
2.54.0