On Sat, 30 Nov 2024 11:40:45 +0000 David Laight <David.Laight@xxxxxxxxxx> 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@xxxxxxxxx> > > Closes: https://lore.kernel.org/oe-kbuild-all/202411230458.dhZwh3TT-lkp@xxxxxxxxx/ > > Closes: https://lore.kernel.org/oe-kbuild-all/202411282222.oF0B4110-lkp@xxxxxxxxx/ > > Fixes: 65f79b501030 ("iio: magnetometer: yas530: Add YAS537 variant") > > Cc: David Laight <david.laight@xxxxxxxxxx> > > Signed-off-by: Jakob Hauser <jahau@xxxxxxxxxxxxxx> > > Reviewed-by: David Laight <david.laight@xxxxxxxxxx> > > 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@xxxxxxxxxxxxxx/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 > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) >
