RE: [PATCH] iio: addac: ad74413r: fix integer promotion bug in ad74413_get_input_current_offset()

[Sa, Nuno]

> From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> Sent: Friday, November 18, 2022 1:32 PM
> To: Tanislav, Cosmin <Cosmin.Tanislav@xxxxxxxxxx>; Lars-Peter Clausen
> <lars@xxxxxxxxxx>; Hennerich, Michael <Michael.Hennerich@xxxxxxxxxx>;
> Jonathan Cameron <jic23@xxxxxxxxxx>
> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>; linux-
> iio@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH] iio: addac: ad74413r: fix integer promotion bug in
> ad74413_get_input_current_offset()
> 
> [External]
> 
> The constant AD74413R_ADC_RESULT_MAX is defined via GENMASK, so its
> type is "unsigned long".
> 
> Hence in the expression voltage_offset * AD74413R_ADC_RESULT_MAX,
> voltage_offset is first promoted to unsigned long, and since it may be
> negative, that results in a garbage value. For example, when range is
> AD74413R_ADC_RANGE_5V_BI_DIR, voltage_offset is -2500 and
> voltage_range is 5000, so the RHS of this assignment is, depending on
> sizeof(long), either 826225UL or 3689348814709142UL, which after
> truncation to int then results in either 826225 or 1972216214 being
> the output from in_currentX_offset.
> 
> Casting to int avoids that promotion and results in the correct -32767
> output.
> 
> Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> ---

After adding proper Fixes: tag,

Reviewed-by: Nuno Sá <nuno.sa@xxxxxxxxxx>