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

[Jonathan Cameron <jic23@kernel.org>]

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
> 
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