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

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Message-ID: <0cec95d3-0520-998e-fba2-de237659f3a1@kernel.org>
Date:   Sun, 2 Apr 2017 10:26:29 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Nikolaus Schulz <nikolaus.schulz@...onic-design.de>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.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 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!

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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