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

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Date:   Sun, 2 Apr 2017 11:15:10 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Lars-Peter Clausen <lars@...afoo.de>,
        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 02/04/17 11:09, Lars-Peter Clausen wrote:
> 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>
Good point.  I'd not thought to check and had forgotten that one.

Applied to the fixes-togreg branch.  Thanks,

Jonathan
> 
>>
>> 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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>>
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>