Re: [PATCH v2 1/2] iio: light: isl29018: fix 32-bit overflow in isl29018_read_lux()

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The patch introduces 64-bit divisions using the standard `/` operator, which will cause a linker error (`undefined reference to __udivdi3`) on 32-bit architectures.
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commit 37588d2a24184ed61a15690c807e6b4b16aa4002
Author: Herman van Hazendonk <github.com@herrie.org>

iio: light: isl29018: fix 32-bit overflow in isl29018_read_lux()

This commit addresses an overflow in isl29018_read_lux() by changing
intermediate calculation variables to u64. It then clamps the final result
to INT_MAX before storing it in the signed output variable.

> diff --git a/drivers/iio/light/isl29018.c b/drivers/iio/light/isl29018.c
> index 1b4c184230489..927018c531e8d 100644
> --- a/drivers/iio/light/isl29018.c
> +++ b/drivers/iio/light/isl29018.c
> @@ -193,17 +193,18 @@ static int isl29018_read_sensor_input(struct isl29018_chip *chip, int mode)
>  static int isl29018_read_lux(struct isl29018_chip *chip, int *lux)
>  {
>  	int lux_data;
> -	unsigned int data_x_range;
> +	u64 data_x_range, result;

[ ... ]

> -	data_x_range = lux_data * chip->scale.scale +
> -		       lux_data * chip->scale.uscale / 1000000;
> -	*lux = data_x_range * chip->calibscale +
> -	       data_x_range * chip->ucalibscale / 1000000;
> +	data_x_range = (u64)lux_data * chip->scale.scale +
> +		       (u64)lux_data * chip->scale.uscale / 1000000;
> +	result = data_x_range * chip->calibscale +
> +		 data_x_range * chip->ucalibscale / 1000000;

[Severity: Low]
Will this cause a linker error on 32-bit architectures?

Since data_x_range and the result of the multiplications are now u64, using
the native division operator (/) for 1000000 will result in an undefined
reference to __udivdi3 when compiling for 32-bit platforms. 

Should this use div_u64() from <linux/math64.h> instead?

> +	*lux = (int)min_t(u64, result, INT_MAX);
>  
>  	return 0;
>  }

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Sashiko AI review · https://sashiko.dev/#/patchset/20260604064925.3097108-1-github.com@herrie.org?part=1