[RFC 1/2] ABI: iio: support AVERAGING_RATIO setting

[Marc Titinger <mtitinger@baylibre.com>]

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@baylibre.com>
---
 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@vger.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@vger.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@vger.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
-- 
1.9.1