linux-kernel - RE: [PATCH] iio: magnetometer: yas530: Use signed integer type for clamp limits

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Message-ID: <a28168acf9374c60902cdb5aa7608dee@AcuMS.aculab.com>
Date: Wed, 27 Nov 2024 08:53:49 +0000
From: David Laight <David.Laight@...LAB.COM>
To: 'Jakob Hauser' <jahau@...ketmail.com>, Jonathan Cameron
	<jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>
CC: Linus Walleij <linus.walleij@...aro.org>, "linux-iio@...r.kernel.org"
	<linux-iio@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, kernel test robot <lkp@...el.com>
Subject: RE: [PATCH] iio: magnetometer: yas530: Use signed integer type for
 clamp limits

From: Jakob Hauser <jahau@...ketmail.com>
> Sent: 26 November 2024 23:40
> 
> In the function yas537_measure() there is a clamp_val() with limits of
> -BIT(13) and  BIT(13) - 1. The input clamp value h[] is of type s32. The BIT()
> is of type unsigned long integer due to its define in include/vdso/bits.h.
> The lower limit -BIT(13) is recognized as -8192 but expressed as an unsigned
> long integer. The size of an unsigned long integer differs between 32-bit and
> 64-bit architectures. Converting this to type s32 may lead to undesired
> behavior.

I think you also need to say that the unsigned divide generates erronous
values on 32bit systems and that the clamp() call result is ignored.

> 
> Declaring a signed integer with a value of BIT(13) allows to use it more
> specifically as a negative value on the lower clamp limit.
> 
> While at it, replace all BIT(13) in the function yas537_measure() by the signed
> integer.
> 
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202411230458.dhZwh3TT-lkp@intel.com/
> Fixes: 65f79b501030 ("iio: magnetometer: yas530: Add YAS537 variant")
> Cc: David Laight <david.laight@...lab.com>
> Signed-off-by: Jakob Hauser <jahau@...ketmail.com>
> ---
> The patch is based on torvalds/linux v6.12.
> 
> The calculation lines h[0], h[1] and h[2] exceed the limit of 80 characters per
> line. In terms of readability I would prefer to keep it that way.
> ---
>  drivers/iio/magnetometer/yamaha-yas530.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/magnetometer/yamaha-yas530.c b/drivers/iio/magnetometer/yamaha-yas530.c
> index 65011a8598d3..938b35536e0d 100644
> --- a/drivers/iio/magnetometer/yamaha-yas530.c
> +++ b/drivers/iio/magnetometer/yamaha-yas530.c
> @@ -372,6 +372,7 @@ static int yas537_measure(struct yas5xx *yas5xx, u16 *t, u16 *x, u16 *y1, u16 *y
>  	u8 data[8];
>  	u16 xy1y2[3];
>  	s32 h[3], s[3];
> +	int half_range = BIT(13);
>  	int i, ret;
> 
>  	mutex_lock(&yas5xx->lock);
> @@ -406,13 +407,13 @@ static int yas537_measure(struct yas5xx *yas5xx, u16 *t, u16 *x, u16 *y1, u16 *y
>  	/* The second version of YAS537 needs to include calibration coefficients */
>  	if (yas5xx->version == YAS537_VERSION_1) {
>  		for (i = 0; i < 3; i++)
> -			s[i] = xy1y2[i] - BIT(13);
> -		h[0] = (c->k *   (128 * s[0] + c->a2 * s[1] + c->a3 * s[2])) / BIT(13);
> -		h[1] = (c->k * (c->a4 * s[0] + c->a5 * s[1] + c->a6 * s[2])) / BIT(13);
> -		h[2] = (c->k * (c->a7 * s[0] + c->a8 * s[1] + c->a9 * s[2])) / BIT(13);
> +			s[i] = xy1y2[i] - half_range;
> +		h[0] = (c->k *   (128 * s[0] + c->a2 * s[1] + c->a3 * s[2])) / half_range;
> +		h[1] = (c->k * (c->a4 * s[0] + c->a5 * s[1] + c->a6 * s[2])) / half_range;
> +		h[2] = (c->k * (c->a7 * s[0] + c->a8 * s[1] + c->a9 * s[2])) / half_range;
>  		for (i = 0; i < 3; i++) {
> -			clamp_val(h[i], -BIT(13), BIT(13) - 1);
> -			xy1y2[i] = h[i] + BIT(13);
> +			clamp_val(h[i], -half_range, half_range - 1);
> +			xy1y2[i] = h[i] + half_range;

NAK - that still ignores the result of clamp.
and it should be clamp() not clamp_val().

	David

>  		}
>  	}
> 
> --
> 2.43.0

-
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