linux-kernel - Re: [PATCH] iio: core: Fix IIO_VAL_FRACTIONAL

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Date:   Sun, 2 Apr 2017 12:09:26 +0200
From:   Lars-Peter Clausen <lars@...afoo.de>
To:     Jonathan Cameron <jic23@...nel.org>,
        Nikolaus Schulz <nikolaus.schulz@...onic-design.de>,
        Hartmut Knaack <knaack.h@....de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        "open list:IIO SUBSYSTEM AND DRIVERS" <linux-iio@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Cc:     stable@...r.kernel.org
Subject: Re: [PATCH] iio: core: Fix IIO_VAL_FRACTIONAL_LOG2 for negative
 values

On 04/02/2017 11:26 AM, Jonathan Cameron wrote:
> On 25/03/17 18:03, Jonathan Cameron wrote:
>> On 24/03/17 12:41, Nikolaus Schulz wrote:
>>> Fix formatting of negative values of type IIO_VAL_FRACTIONAL_LOG2 by
>>> switching from do_div(), which can't handle negative numbers, to
>>> div_s64_rem().  Also use shift_right for shifting, which is safe with
>>> negative values.
>>>
>>> Signed-off-by: Nikolaus Schulz <nikolaus.schulz@...onic-design.de>
>>> Cc: stable@...r.kernel.org
>> Looks sane to me, but I'd like to give others time to comment on this
>> just in case there is some odd condition neither of us has thought of!
>>
>> Give me a poke if we get nothing else for a few weeks.
> Lars, I think this might have been your magic in the first place.
> 
> Could you sanity check this one please. It's in the category of very
> risky of both Nikolaus and I have missed something!

It's the same as this:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/iio/industrialio-core.c?id=171c0091837c81ed5c949fec6966bb5afff2d1cf

Should be OK.

Reviewed-by: Lars-Peter Clausen <lars@...afoo.de>

> 
> Thanks,
> 
> Jonathan
>>
>> Jonathan
>>> ---
>>>  drivers/iio/industrialio-core.c | 7 +++----
>>>  1 file changed, 3 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>>> index d18ded4..3ff91e0 100644
>>> --- a/drivers/iio/industrialio-core.c
>>> +++ b/drivers/iio/industrialio-core.c
>>> @@ -610,10 +610,9 @@ static ssize_t __iio_format_value(char *buf, size_t len, unsigned int type,
>>>  		tmp0 = (int)div_s64_rem(tmp, 1000000000, &tmp1);
>>>  		return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
>>>  	case IIO_VAL_FRACTIONAL_LOG2:
>>> -		tmp = (s64)vals[0] * 1000000000LL >> vals[1];
>>> -		tmp1 = do_div(tmp, 1000000000LL);
>>> -		tmp0 = tmp;
>>> -		return snprintf(buf, len, "%d.%09u", tmp0, tmp1);
>>> +		tmp = shift_right((s64)vals[0] * 1000000000LL, vals[1]);
>>> +		tmp0 = (int)div_s64_rem(tmp, 1000000000LL, &tmp1);
>>> +		return snprintf(buf, len, "%d.%09u", tmp0, abs(tmp1));
>>>  	case IIO_VAL_INT_MULTIPLE:
>>>  	{
>>>  		int i;
>>>
>>
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