Re: [PATCH v2 1/2] iio:humidity:si7020: replaced bitmask on humidity values with range check

[Hartmut Knaack <knaack.h@gmx.de>]

Nicola Corna schrieb am 23.08.2015 um 09:41:
> August 22 2015 11:54 PM, "Hartmut Knaack" <knaack.h@gmx.de> wrote:
>> Hartmut Knaack schrieb am 22.08.2015 um 23:44:
>>
>>> Nicola Corna schrieb am 22.08.2015 um 20:01:
>>>> The maximum possible value for the relative humidity is 55575 (100%RH).
>>>> This value, if shifted right by 2 bits, uses 14 bits and masking it with
>>>> a 12 bit mask removes 2 meaningful bits.
>>>> The masking has been replaced with a range check that sets the minimum
>>>> value at 786 (0%RH) and the maximum at 13894 (100%RH).
>>>>
>>>> Signed-off-by: Nicola Corna <nicola@corna.info>
>>>
>>> Might be discussable, if we want the upper boundary to be rounded down,
>>> so we just barely reach 100% rather than slightly exceeding it (in numbers,
>>> that is 99,998 vs 100,006). Using 13893 might be the better value. Other
>>> than that (and a typo in the comment) looking good, so:
>>> Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
>>
>> On second thought, this is not exactly how clamp_val works. It will return
>> a value between the boundaries, so usage is like this:
>> *val = clamp_val(*val, 786, 13894)
>>
> 
> I've tested clamp_val(*val, 786, 13894) and the minimum returned value is 786
> while the maximum is 13894; shouldn't the line be like this?
> *val = clamp_val(*val, 786, 13893)
> Now the minimum value is 786 (exactly 0%RH), while the maximum (as you pointed
> out) is 13893 (99,998%RH).
> 
> Nicola Corna
> 

Using 13893 as top boundary is my preference, although I would not
completely object against 13894. So either way would be fine with me.

>> If my suggestions are addressed, you can keep my Reviewed-by tag.
>> Thanks,
>>
>> Hartmut
>>
>>>> ---
>>>> drivers/iio/humidity/si7020.c | 6 +++++-
>>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>>>> index fa3b809..d27e2f2 100644
>>>> --- a/drivers/iio/humidity/si7020.c
>>>> +++ b/drivers/iio/humidity/si7020.c
>>>> @@ -57,8 +57,12 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>>>> if (ret < 0)
>>>> return ret;
>>>> *val = ret >> 2;
>>>> + /*
>>>> + * Humidity values can sligthly exceed the 0-100%RH
>>>
>>> Typo: slightly
>>>
>>>> + * range and should be corrected by software
>>>> + */
>>>> if (chan->type == IIO_HUMIDITYRELATIVE)
>>>> - *val &= GENMASK(11, 0);
>>>> + clamp_val(*val, 786, 13894);
>>>> return IIO_VAL_INT;
>>>> case IIO_CHAN_INFO_SCALE:
>>>> if (chan->type == IIO_TEMP)
>>>
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