[PATCH 2/3] iio: max31856: add support for configuring the HW averaging

[Andrea Merello <andrea.merello@gmail.com>]

This sensor can perform samples averaging in hardware, but currently the
driver leaves this setting alone (default is no averaging).

This patch introduces a new IIO attribute that allows the user to set the
averaging as desired (the HW supports averaging of 2, 5, 8 or 16 samples)

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
---
 drivers/iio/temperature/max31856.c | 43 ++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
index d12613f7ba3c..8b2e0102fa5c 100644
--- a/drivers/iio/temperature/max31856.c
+++ b/drivers/iio/temperature/max31856.c
@@ -24,6 +24,8 @@
 #define MAX31856_CR0_OCFAULT       BIT(4)
 #define MAX31856_CR0_OCFAULT_MASK  GENMASK(5, 4)
 #define MAX31856_CR0_FILTER_50HZ   BIT(0)
+#define MAX31856_AVERAGING_MASK    GENMASK(6, 4)
+#define MAX31856_AVERAGING_SHIFT   4
 #define MAX31856_TC_TYPE_MASK      GENMASK(3, 0)
 #define MAX31856_FAULT_OVUV        BIT(1)
 #define MAX31856_FAULT_OPEN        BIT(0)
@@ -65,6 +67,7 @@ struct max31856_data {
 	struct spi_device *spi;
 	u32 thermocouple_type;
 	bool filter_50hz;
+	int averaging;
 };
 
 static int max31856_read(struct max31856_data *data, u8 reg,
@@ -109,6 +112,10 @@ static int max31856_init(struct max31856_data *data)
 
 	reg_cr1_val &= ~MAX31856_TC_TYPE_MASK;
 	reg_cr1_val |= data->thermocouple_type;
+
+	reg_cr1_val &= ~MAX31856_AVERAGING_MASK;
+	reg_cr1_val |= data->averaging << MAX31856_AVERAGING_SHIFT;
+
 	ret = max31856_write(data, MAX31856_CR1_REG, reg_cr1_val);
 	if (ret)
 		return ret;
@@ -295,14 +302,50 @@ static ssize_t set_filter(struct device *dev,
 	return len;
 }
 
+static ssize_t show_averaging(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct max31856_data *data = iio_priv(indio_dev);
+
+	return sprintf(buf, "%d\n", 1 << data->averaging);
+}
+
+static ssize_t set_averaging(struct device *dev,
+			     struct device_attribute *attr,
+			     const char *buf,
+			     size_t len)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct max31856_data *data = iio_priv(indio_dev);
+	unsigned int nsamples;
+	int shift;
+	int ret;
+
+	ret = kstrtouint(buf, 10, &nsamples);
+	if (ret)
+		return ret;
+
+	shift = fls(nsamples) - 1;
+	if (nsamples > 16 || BIT(shift) != nsamples)
+		return -EINVAL;
+
+	data->averaging = shift;
+	max31856_init(data);
+	return len;
+}
+
 static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
 static IIO_DEVICE_ATTR(fault_oc, 0444, show_fault_oc, NULL, 0);
 static IIO_DEVICE_ATTR(filter, 0644, show_filter, set_filter, 0);
+static IIO_DEVICE_ATTR(averaging, 0644, show_averaging, set_averaging, 0);
 
 static struct attribute *max31856_attributes[] = {
 	&iio_dev_attr_fault_ovuv.dev_attr.attr,
 	&iio_dev_attr_fault_oc.dev_attr.attr,
 	&iio_dev_attr_filter.dev_attr.attr,
+	&iio_dev_attr_averaging.dev_attr.attr,
 	NULL,
 };
 
-- 
2.17.1