linux-kernel - Re: [RFC 1/2] ABI: iio: support AVERAGING

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Date:	Tue, 17 Nov 2015 13:39:43 +0000
From:	jic23@...23.retrosnub.co.uk
To:	Marc Titinger <mtitinger@...libre.com>
Cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net, daniel.baluta@...el.com,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org
Subject: Re: [RFC 1/2] ABI: iio: support AVERAGING_RATIO setting

On 17.11.2015 10:44, Marc Titinger wrote:
> Some ADC devices allow averaging/downsampling. The minimal parameter
> set for this will be the number of taps used for computing a mean 
> value.
> 
> In some cases the ratio will hold discrete values for instance "1, 4, 
> 16"
> hence an averaging_ratio_available property is useful. The possible 
> ratio
> values are less likely to changing with the device settings, so this 
> patch
> only provides a CONST version of the definition helper.
> 
> Tested with ina226:
> 
> # ls /sys/bus/iio/devices/iio\:device0/
> averaging_ratio_available     in_voltage0_raw
> dev                           in_voltage1_raw
> in_averaging_ratio            name
> in_calibscale                 power
> in_current2_raw               sampling_frequency_available
> in_power3_raw                 subsystem
> in_sampling_frequency         uevent
> 
> # cat averaging_ratio_available
> 1, 4, 16, 64, 128, 256, 512, 1024
> 
> Signed-off-by: Marc Titinger <mtitinger@...libre.com>
Having just noted the previous element we added was oversampling_ratio,
in a sense they are somewhat similar.

To play Devil's advocate...
Could we in theory just use that as it is existing ABI?

oversampling_ratio was introduced for the bmc150.
That particular part doesn't have the worlds clearest datasheet
but it seems like it's effectively specifying how many repeat 
measurements
to average.

I'm afraid I'd completely forgotten about this or
I would have mentioned it earlier!

Jonathan

> ---
>  Documentation/ABI/testing/sysfs-bus-iio | 13 +++++++++++++
>  drivers/iio/industrialio-core.c         |  1 +
>  include/linux/iio/iio.h                 |  1 +
>  include/linux/iio/sysfs.h               |  9 +++++++++
>  4 files changed, 24 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio
> b/Documentation/ABI/testing/sysfs-bus-iio
> index 42d360f..a208dfe 100644
> --- a/Documentation/ABI/testing/sysfs-bus-iio
> +++ b/Documentation/ABI/testing/sysfs-bus-iio
> @@ -56,6 +56,19 @@ Description:
>  		When the internal sampling clock can only take a small
>  		discrete set of values, this file lists those available.
> 
> +What:		/sys/bus/iio/devices/iio:deviceX/averaging_ratio
> +KernelVersion:	4.x.x
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Hardware dependent ADC averaging. Controls the averaging ratio
> +		of the digital filter if available.
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/averaging_ratio_available
> +KernelVersion:	4.x.x
> +Contact:	linux-iio@...r.kernel.org
> +Description:
> +		Hardware dependent values supported by the averaging filter.
> +
>  What:		/sys/bus/iio/devices/iio:deviceX/oversampling_ratio
>  KernelVersion:	2.6.38
>  Contact:	linux-iio@...r.kernel.org
> diff --git a/drivers/iio/industrialio-core.c 
> b/drivers/iio/industrialio-core.c
> index b3fcc2c..e4745f0 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -142,6 +142,7 @@ static const char * const iio_chan_info_postfix[] = 
> {
>  	[IIO_CHAN_INFO_DEBOUNCE_TIME] = "debounce_time",
>  	[IIO_CHAN_INFO_CALIBEMISSIVITY] = "calibemissivity",
>  	[IIO_CHAN_INFO_OVERSAMPLING_RATIO] = "oversampling_ratio",
> +	[IIO_CHAN_INFO_AVERAGING_RATIO] = "averaging_ratio",
>  };
> 
>  /**
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 7bb7f67..4c84de5 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -46,6 +46,7 @@ enum iio_chan_info_enum {
>  	IIO_CHAN_INFO_DEBOUNCE_TIME,
>  	IIO_CHAN_INFO_CALIBEMISSIVITY,
>  	IIO_CHAN_INFO_OVERSAMPLING_RATIO,
> +	IIO_CHAN_INFO_AVERAGING_RATIO,
>  };
> 
>  enum iio_shared_by {
> diff --git a/include/linux/iio/sysfs.h b/include/linux/iio/sysfs.h
> index 9cd8f74..4478ba1 100644
> --- a/include/linux/iio/sysfs.h
> +++ b/include/linux/iio/sysfs.h
> @@ -76,6 +76,15 @@ struct iio_const_attr {
>  /* Generic attributes of onetype or another */
> 
>  /**
> + * IIO_CONST_ATTR_AVERAGING_RATIO_AVAIL - list available averaging 
> ratios
> + * @_string: ratio string for the attribute
> + *
> + * Constant version
> + **/
> +#define IIO_CONST_ATTR_AVERAGING_RATIO_AVAIL(_string)                 
> \
> +	IIO_CONST_ATTR(averaging_ratio_available, _string)
> +
> +/**
>   * IIO_DEV_ATTR_SAMP_FREQ - sets any internal clock frequency
>   * @_mode: sysfs file mode/permissions
>   * @_show: output method for the attribute

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