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

["Nicola Corna" <nicola@corna.info>]

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

> 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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