Re: [PATCH v1 1/1] iio:core: fix IIO_VAL_FRACTIONAL sign handling

[Gregor Boirie <gregor.boirie@parrot.com>]

Just to mention that a somewhat similar patch might be needed to handle 
negative
IIO_VAL_FRACTIONAL_LOG2 values.

On 09/05/2016 10:24 PM, Jonathan Cameron wrote:
> On 05/09/16 08:59, Lars-Peter Clausen wrote:
>> On 09/03/2016 05:13 PM, Jonathan Cameron wrote:
>>> On 02/09/16 19:27, Gregor Boirie wrote:
>>>> 7985e7c100 ("iio: Introduce a new fractional value type") introduced a
>>>> new IIO_VAL_FRACTIONAL value type meant to represent rational type numbers
>>>> expressed by a numerator and denominator combination.
>>>>
>>>> Formating of IIO_VAL_FRACTIONAL values relies upon do_div() usage. This
>>>> fails handling negative values properly since parameters are reevaluated
>>>> as unsigned values.
>>>> Fix this by using div_s64_rem() instead. Computed integer part will carry
>>>> properly signed value. Formatted fractional part will always be positive.
>>>>
>>>> Fixes: 7985e7c100 ("iio: Introduce a new fractional value type")
>>>> Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
>>> Hi Gregor,
>>>
>>> While this looks sensible to me, I always gain an almighty headache when
>>> I hit the various divide functions.
>>>
>>> Lars, the fractional code was yours in the first place.
>>> If you have time can you sanity check this please.
>> Looks good. While looking into this I noticed that we have a very similar
>> patch[1] in our tree, seems like somebody forgot to send that upstream.
>>
>> Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
> Applied to the fixes-togreg branch of iio.git and marked for stable.
> Good to know about the previous patch - if there was anything hiding around
> this I would assume that would have shaken it out by now!
>
> Thanks
>
> Jonathan
>>
>> [1]
>> https://github.com/analogdevicesinc/linux/commit/1dbcdcfd0c8d3f5513572697685d9f30ba49d851
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-iio" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>