Re: [PATCH 1/4] iio: Add INT_TIME (integration time) channel info attribute

[Jonathan Cameron <jic23@kernel.org>]

On 09/08/13 16:20, Peter Meerwald wrote:
> Integration time is in seconds; it controls the measurement
> time and influences the gain of a sensor.
> 
> There are two typical ways that scaling is implemented in a device:
> 1) input amplifier,
> 2) reference to the ADC is changed.
> These both result in the accuracy of the ADC varying (by applying its
> sampling over a more relevant range).
> 
> Integration time is a way of dealing with noise inherent in the analog
> sensor itself.  In the case of a light sensor, a mixture of photon noise
> and device specific noise.  Photon noise is dealt with by either improving
> the efficiency of the sensor, (more photons actually captured) which is not
> easily varied dynamically, or by integrating the measurement over a longer
> time period.  Note that this can also be thought of as an averaging of a
> number of individual samples and is infact sometimes implemented this way.
> Altering integration time implies that the duration of a measurement changes,
> a fact the device's user may be interested in.
> 
> Hence it makes sense to distinguish between integration time and simple
> scale. In some devices both types of control are present and whilst they
> will have similar effects on the amplitude of the reading, their effect
> on the noise of the measurements will differ considerably.
> 
> Used by adjd_s311, tsl4531, tcs3472
> The following drivers have similar controls (and could be adapted):
> * tsl2563 (integration time is controlled via CALIBSCALE among other things)
> * tsl2583 (has integration_time device_attr, but driver doesn't use channels yet)
> * tsl2x7x (has integration_time attr)
> 
> Signed-off-by: Peter Meerwald <pmeerw@pmeerw.net>
> Cc: Jon Brenner <jon.brenner@ams.com>
We may want to put some of this detail into the abi document if we get many
people trying to use this for the wrong purpose.  Anyhow
Applied to the togreg branch of iio.git

Thanks,

> ---
>  Documentation/ABI/testing/sysfs-bus-iio |   12 ++++++++++++
>  drivers/iio/industrialio-core.c         |    1 +
>  include/linux/iio/iio.h                 |    1 +
>  include/linux/iio/sysfs.h               |   15 +++++++++++++++
>  4 files changed, 29 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
> index 5caaab9..d75147c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-iio
> +++ b/Documentation/ABI/testing/sysfs-bus-iio
> @@ -800,3 +800,15 @@ Description:
>  		Writing '1' stores the current device configuration into
>  		on-chip EEPROM. After power-up or chip reset the device will
>  		automatically load the saved configuration.
> +
> +What:		/sys/.../iio:deviceX/in_intensity_red_integration_time
> +What:		/sys/.../iio:deviceX/in_intensity_green_integration_time
> +What:		/sys/.../iio:deviceX/in_intensity_blue_integration_time
> +What:		/sys/.../iio:deviceX/in_intensity_clear_integration_time
> +What:		/sys/.../iio:deviceX/in_illuminance_integration_time
> +KernelVersion:	3.12
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		This attribute is used to get/set the integration time in
> +		seconds.
> +
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 97f0297..2cb4841 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -101,6 +101,7 @@ static const char * const iio_chan_info_postfix[] = {
>  	[IIO_CHAN_INFO_PHASE] = "phase",
>  	[IIO_CHAN_INFO_HARDWAREGAIN] = "hardwaregain",
>  	[IIO_CHAN_INFO_HYSTERESIS] = "hysteresis",
> +	[IIO_CHAN_INFO_INT_TIME] = "integration_time",
>  };
>  
>  const struct iio_chan_spec
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 8e7a813..01edd67 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -36,6 +36,7 @@ enum iio_chan_info_enum {
>  	IIO_CHAN_INFO_PHASE,
>  	IIO_CHAN_INFO_HARDWAREGAIN,
>  	IIO_CHAN_INFO_HYSTERESIS,
> +	IIO_CHAN_INFO_INT_TIME,
>  };
>  
>  enum iio_endian {
> diff --git a/include/linux/iio/sysfs.h b/include/linux/iio/sysfs.h
> index 2958c96..8a1d186 100644
> --- a/include/linux/iio/sysfs.h
> +++ b/include/linux/iio/sysfs.h
> @@ -100,6 +100,21 @@ struct iio_const_attr {
>  #define IIO_CONST_ATTR_SAMP_FREQ_AVAIL(_string)			\
>  	IIO_CONST_ATTR(sampling_frequency_available, _string)
>  
> +/**
> + * IIO_DEV_ATTR_INT_TIME_AVAIL - list available integration times
> + * @_show: output method for the attribute
> + **/
> +#define IIO_DEV_ATTR_INT_TIME_AVAIL(_show)		\
> +	IIO_DEVICE_ATTR(integration_time_available, S_IRUGO, _show, NULL, 0)
> +/**
> + * IIO_CONST_ATTR_INT_TIME_AVAIL - list available integration times
> + * @_string: frequency string for the attribute
> + *
> + * Constant version
> + **/
> +#define IIO_CONST_ATTR_INT_TIME_AVAIL(_string)		\
> +	IIO_CONST_ATTR(integration_time_available, _string)
> +
>  #define IIO_DEV_ATTR_TEMP_RAW(_show)			\
>  	IIO_DEVICE_ATTR(in_temp_raw, S_IRUGO, _show, NULL, 0)
>  
>