David Lechner e2c68cea43 hwmon: (tmp513) Fix division of negative numbers ...

Fix several issues with division of negative numbers in the tmp513
driver.

The docs on the DIV_ROUND_CLOSEST macro explain that dividing a negative
value by an unsigned type is undefined behavior. The driver was doing
this in several places, i.e. data->shunt_uohms has type of u32. The
actual "undefined" behavior is that it converts both values to unsigned
before doing the division, for example:

    int ret = DIV_ROUND_CLOSEST(-100, 3U);

results in ret == 1431655732 instead of -33.

Furthermore the MILLI macro has a type of unsigned long. Multiplying a
signed long by an unsigned long results in an unsigned long.

So, we need to cast both MILLI and data data->shunt_uohms to long when
using the DIV_ROUND_CLOSEST macro.

Fixes: f07f9d2467 ("hwmon: (tmp513) Use SI constants from units.h")
Fixes: 59dfa75e5d ("hwmon: Add driver for Texas Instruments TMP512/513 sensor chips.")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://lore.kernel.org/r/20250114-fix-si-prefix-macro-sign-bugs-v1-1-696fd8d10f00@baylibre.com
[groeck: Drop some continuation lines]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

2025-01-14 15:42:16 -08:00

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