linux-kernel - [PATCH v2] iio: magnetometer: yas530: Use signed integer type for clamp limits

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Message-Id: <11609b2243c295d65ab4d47e78c239d61ad6be75.1732914810.git.jahau@rocketmail.com>
Date: Fri, 29 Nov 2024 22:25:07 +0100
From: Jakob Hauser <jahau@...ketmail.com>
To: Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>
Cc: David Laight <david.laight@...lab.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Jakob Hauser <jahau@...ketmail.com>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH v2] iio: magnetometer: yas530: Use signed integer type for clamp limits

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.

Additionally, in the calculation lines h[0], h[1] and h[2] the unsigned long
integer divisor BIT(13) causes an unsigned division, shifting the left-hand
side of the equation back and forth, possibly ending up in large positive
values instead of negative values on 32-bit architectures.

To solve those two issues, declare a signed integer with a value of BIT(13).

There is another omission in the clamp line: clamp_val() returns a value and
it's going nowhere here. Self-assign it to h[i] to make use of the clamp
macro.

Finally, replace clamp_val() macro by clamp() because after changing the limits
from type unsigned long integer to signed integer it's fine that way.

Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202411230458.dhZwh3TT-lkp@intel.com/
Closes: https://lore.kernel.org/oe-kbuild-all/202411282222.oF0B4110-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.

Changes in v2:
 - Self-assigned the clamp macro to h[i].
 - Changed from clamp_val() macro to clamp().
 - In commit message added issues on divisor BIT(13) and missing clamp
   assignment.
 - In tags added another (duplicate) report by the kernel test robot.

Link to v1: https://lore.kernel.org/linux-iio/20241126234021.19749-1-jahau@rocketmail.com/T/#t
---
 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..c55a38650c0d 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);
+			h[i] = clamp(h[i], -half_range, half_range - 1);
+			xy1y2[i] = h[i] + half_range;
 		}
 	}
 
-- 
2.43.0