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Message-ID: <20241130143506.53973e40@jic23-huawei>
Date: Sat, 30 Nov 2024 14:35:06 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: David Laight <David.Laight@...LAB.COM>
Cc: 'Jakob Hauser' <jahau@...ketmail.com>, Lars-Peter Clausen
<lars@...afoo.de>, Andrew Morton <akpm@...ux-foundation.org>, 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 v2] iio: magnetometer: yas530: Use signed integer type
for clamp limits
On Sat, 30 Nov 2024 11:40:45 +0000
David Laight <David.Laight@...LAB.COM> wrote:
> From: Jakob Hauser
>
> Copying Andrew M - he might want to take this through his mm tree.
I'm confused. Why?
Looks like a local bug in an IIO driver. What am I missing?
>
> > Sent: 29 November 2024 21:25
> >
> > 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>
>
> Reviewed-by: David Laight <david.laight@...lab.com>
>
> I THINK all the other BIT() and GENMASK() are ok.
> The code also rather heavily relies on u16 being promoted to 'signed int'.
>
> David
>
>
> > ---
> > 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
>
> -
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