Re: [PATCH 4/8] iio: core: Introduce IO_CHAN_INFO_CALIBWEIGHT

[Jonathan Cameron <jic23@kernel.org>]

On 29/12/14 15:05, Tirdea, Irina wrote:
> 
> 
>> -----Original Message-----
>> From: Jonathan Cameron [mailto:jic23@kernel.org]
>> Sent: 26 December, 2014 15:31
>> To: Tirdea, Irina; linux-iio@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org; Dogaru, Vlad; Baluta, Daniel; Hartmut Knaack; Lars-Peter Clausen; Peter Meerwald
>> Subject: Re: [PATCH 4/8] iio: core: Introduce IO_CHAN_INFO_CALIBWEIGHT
>>
>> On 19/12/14 22:57, Irina Tirdea wrote:
>>> Some devices need the weight of the user to compute other
>>> parameters. One of this devices is Freescale's MMA9553L
>>> (http://www.freescale.com/files/sensors/doc/ref_manual/MMA9553LSWRM.pdf)
>>> that needs the weight of the user to compute the number of calories burnt.
>>>
>>> Signed-off-by: Irina Tirdea <irina.tirdea@intel.com>
>>> ---
>>>  Documentation/ABI/testing/sysfs-bus-iio |    7 +++++++
>>>  drivers/iio/industrialio-core.c         |    1 +
>>>  include/linux/iio/iio.h                 |    1 +
>>>  3 files changed, 9 insertions(+)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
>>> index 07acef7..e480175 100644
>>> --- a/Documentation/ABI/testing/sysfs-bus-iio
>>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
>>> @@ -351,6 +351,13 @@ Description:
>>>  		to compute the stride length, distance, speed and activity
>>>  		type.
>>>
>>> +What:		/sys/bus/iio/devices/iio:deviceX/in_steps_calibweight
>>> +KernelVersion:	3.19
>>> +Contact:	linux-iio@vger.kernel.org
>>> +Description:
>>> +		Weight of the user (in kg). It is needed by some pedometers
>>> +		to compute the calories burnt by the user.
>> How about grams?  Nice to keep to SI units going forward (I appreciate we
>> have broken that for what seemed like good reasons at the time) in one
>> or two places, but it makes it much harder to define consistent interfaces in the
>> long run.
> 
> According to SI [1] kg is the base unit for mass, so this was the obvious first choice.
I'd forgotten that piece if 'entirely intuitive' unit choice ;)

> I have nothing against using grams, but it is not clear to me why using grams would make it easier to define consistent interfaces in the long run.
> I am probably missing something, so could you please clarify this?
kg fine as we have a good argument for why ;)

The consistent interface bit comes when we start getting compound units if we had picked
non SI choices (such is mA and mV - which we are stuck with unfortunately).
Now as Joules are kg m^2 s^-2 for example, we are on good grounds with the kg.
> 
> Thanks,
> Irina
> 
> [1] http://www.bipm.org/en/measurement-units/
> 
>> J
>>> +
>>>  What:		/sys/bus/iio/devices/iio:deviceX/in_accel_scale_available
>>>  What:		/sys/.../iio:deviceX/in_voltageX_scale_available
>>>  What:		/sys/.../iio:deviceX/in_voltage-voltage_scale_available
>>> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
>>> index 5e50aca..4c435c8 100644
>>> --- a/drivers/iio/industrialio-core.c
>>> +++ b/drivers/iio/industrialio-core.c
>>> @@ -124,6 +124,7 @@ static const char * const iio_chan_info_postfix[] = {
>>>  	[IIO_CHAN_INFO_INT_TIME] = "integration_time",
>>>  	[IIO_CHAN_INFO_ENABLE] = "en",
>>>  	[IIO_CHAN_INFO_CALIBHEIGHT] = "calibheight",
>>> +	[IIO_CHAN_INFO_CALIBWEIGHT] = "calibweight",
>>>  };
>>>
>>>  /**
>>> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
>>> index 878d861..752a929 100644
>>> --- a/include/linux/iio/iio.h
>>> +++ b/include/linux/iio/iio.h
>>> @@ -40,6 +40,7 @@ enum iio_chan_info_enum {
>>>  	IIO_CHAN_INFO_INT_TIME,
>>>  	IIO_CHAN_INFO_ENABLE,
>>>  	IIO_CHAN_INFO_CALIBHEIGHT,
>>> +	IIO_CHAN_INFO_CALIBWEIGHT,
>>>  };
>>>
>>>  enum iio_shared_by {
>>>
>