ASoC: tas2770: Fix order of operations for temperature calculation

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@gmail.com>
Link: https://patch.msgid.link/20260425-tas27xx-hwmon-fixes-v1-3-83c13b8e8f54@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/sound/soc/codecs/tas2770.c b/sound/soc/codecs/tas2770.c
index d4d7d056141bd740a9a0cf93eaaa70ef689c395f..50501bcbe916780bea25acf12763c35facd78a3a 100644 (file)
--- 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;
 }