Re: [PATCH] iio: core: Fix IIO_VAL_FRACTIONAL_LOG2 for negative values

From: Jonathan Cameron
Date: Sun Apr 02 2017 - 06:15:38 EST


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@xxxxxxxxxxxxxxxxx>
>>>> Cc: stable@xxxxxxxxxxxxxxx
>>> 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@xxxxxxxxxx>
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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>