August 22 2015 7:21 PM, "Jonathan Cameron" <jic23@xxxxxxxxxx> wrote:
> On 20/08/15 15:11, Nicola Corna wrote:
>
>> The value given by the Si7013/20/21 modules needs a conversion using a
>> small expression in order to obtain the measurement in °C or %RH. This
>> patch adds the computation inside the si7020 module, allowing the user to
>> obtain the measurement in m°C and 10E-3%RH without any additional
>> calculation.
>>
>> Signed-off-by: Nicola Corna <nicola@xxxxxxxxxx>
>
> What is the benefit in doing this? Userspace already has all the numbers
> to calculate the value? The calculation is trivial to do in userspace.
> The basic principle of IIO is to do as little as possible in the driver
> and to leave such calculations to userspace which has the benefit of
> easy access to floating point calculations if desired.
>
> So sorry, not taking this one.
>
> Jonathan
>
Ok, thanks anyway.
>> ---
>> drivers/iio/humidity/si7020.c | 18 ++++++++++++++++--
>> 1 file changed, 16 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iio/humidity/si7020.c b/drivers/iio/humidity/si7020.c
>> index a8bad04..c534706 100644
>> --- a/drivers/iio/humidity/si7020.c
>> +++ b/drivers/iio/humidity/si7020.c
>> @@ -70,6 +70,7 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>>
>> switch (mask) {
>> case IIO_CHAN_INFO_RAW:
>> + case IIO_CHAN_INFO_PROCESSED:
>> if (holdmode) {
>> ret = i2c_smbus_read_word_data(*client,
>> chan->type == IIO_TEMP ?
>> @@ -108,6 +109,17 @@ static int si7020_read_raw(struct iio_dev *indio_dev,
>> else if (*val > 55575) /* 100%RH */
>> *val = 55575;
>> }
>> + if (mask == IIO_CHAN_INFO_PROCESSED) {
>> + /*
>> + * To avoid overflows the fractions can be simplified:
>> + * temperature --> 175720 / (65536 >> 2) = 21965 / 2048
>> + * humidity --> 125000 / (65536 >> 2) = 15625 / 2048
>> + */
>> + if (chan->type == IIO_TEMP)
>> + *val = (*val - 4368) * 21965 / 2048;
>> + else
>> + *val = (*val - 768) * 15625 / 2048;
>> + }
>> return IIO_VAL_INT;
>> case IIO_CHAN_INFO_SCALE:
>> if (chan->type == IIO_TEMP)
>> @@ -142,12 +154,14 @@ static const struct iio_chan_spec si7020_channels[] = {
>> {
>> .type = IIO_HUMIDITYRELATIVE,
>> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
>> - BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
>> + BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |
>> + BIT(IIO_CHAN_INFO_PROCESSED),
>> },
>> {
>> .type = IIO_TEMP,
>> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
>> - BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET),
>> + BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_OFFSET) |
>> + BIT(IIO_CHAN_INFO_PROCESSED),
>> }
>> };
--
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