iio: hmc5843: Add attributes for measurement config of bias current

Change static attribute meas_conf for bias current configuration
to channel attribute in_magn_meas_conf and also add
in_magn_meas_conf_available attribute to view available configurations.

This patch solves functionality bug: driver was using same function
hmc5843_set_measurement_configuration for setting bias current config
for all device types but the function was returning -EINVAL for any
setting >= 0x03 although, for sensor HMC5983, value 3 is valid.

API for setting bias measurement configuration:

normal - 	Normal measurement configuration (default):
		In normal measurement configuration the device
		follows normal measurement flow. Pins BP and BN
		are left floating and high impedance.

positivebias - 	Positive bias configuration: In positive bias
		configuration, a positive current is forced across
		the resistive load on pins BP and BN.

negativebias - 	Negative bias configuration. In negative bias
		configuration, a negative current is forced across
		the resistive load on pins BP and BN.

disabled     - 	Only available on HMC5983. Magnetic sensor is disabled.
		Temperature sensor is enabled.

Signed-off-by: Cristina Moraru <cristina.moraru09@gmail.com>
Cc: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/magnetometer/hmc5843_core.c

@@ -66,6 +66,33 @@
 #define HMC5843_MEAS_CONF_NEGATIVE_BIAS		0x02
 #define HMC5843_MEAS_CONF_MASK			0x03
 
+/*
+ * API for setting the measurement configuration to
+ * Normal, Positive bias and Negative bias
+ *
+ * From the datasheet:
+ * 0 - Normal measurement configuration (default): In normal measurement
+ *     configuration the device follows normal measurement flow. Pins BP
+ *     and BN are left floating and high impedance.
+ *
+ * 1 - Positive bias configuration: In positive bias configuration, a
+ *     positive current is forced across the resistive load on pins BP
+ *     and BN.
+ *
+ * 2 - Negative bias configuration. In negative bias configuration, a
+ *     negative current is forced across the resistive load on pins BP
+ *     and BN.
+ *
+ * 3 - Only available on HMC5983. Magnetic sensor is disabled.
+ *     Temperature sensor is enabled.
+ */
+
+static const char *const hmc5843_meas_conf_modes[] = {"normal", "positivebias",
+						      "negativebias"};
+
+static const char *const hmc5983_meas_conf_modes[] = {"normal", "positivebias",
+						      "negativebias",
+						      "disabled"};
 /* Scaling factors: 10000000/Gain */
 static const int hmc5843_regval_to_nanoscale[] = {
 	6173, 7692, 10309, 12821, 18868, 21739, 25641, 35714
@@ -174,24 +201,6 @@ static int hmc5843_read_measurement(struct hmc5843_data *data,
 	return IIO_VAL_INT;
 }
 
-/*
- * API for setting the measurement configuration to
- * Normal, Positive bias and Negative bias
- *
- * From the datasheet:
- * 0 - Normal measurement configuration (default): In normal measurement
- *     configuration the device follows normal measurement flow. Pins BP
- *     and BN are left floating and high impedance.
- *
- * 1 - Positive bias configuration: In positive bias configuration, a
- *     positive current is forced across the resistive load on pins BP
- *     and BN.
- *
- * 2 - Negative bias configuration. In negative bias configuration, a
- *     negative current is forced across the resistive load on pins BP
- *     and BN.
- *
- */
 static int hmc5843_set_meas_conf(struct hmc5843_data *data, u8 meas_conf)
 {
 	int ret;
@@ -205,48 +214,55 @@ static int hmc5843_set_meas_conf(struct hmc5843_data *data, u8 meas_conf)
 }
 
 static
-ssize_t hmc5843_show_measurement_configuration(struct device *dev,
-					       struct device_attribute *attr,
-					       char *buf)
+int hmc5843_show_measurement_configuration(struct iio_dev *indio_dev,
+					   const struct iio_chan_spec *chan)
 {
-	struct hmc5843_data *data = iio_priv(dev_to_iio_dev(dev));
+	struct hmc5843_data *data = iio_priv(indio_dev);
 	unsigned int val;
 	int ret;
 
 	ret = regmap_read(data->regmap, HMC5843_CONFIG_REG_A, &val);
 	if (ret)
 		return ret;
-	val &= HMC5843_MEAS_CONF_MASK;
 
-	return sprintf(buf, "%d\n", val);
+	return val & HMC5843_MEAS_CONF_MASK;
 }
 
 static
-ssize_t hmc5843_set_measurement_configuration(struct device *dev,
-					      struct device_attribute *attr,
-					      const char *buf,
-					      size_t count)
+int hmc5843_set_measurement_configuration(struct iio_dev *indio_dev,
+					  const struct iio_chan_spec *chan,
+					  unsigned int meas_conf)
 {
-	struct hmc5843_data *data = iio_priv(dev_to_iio_dev(dev));
-	unsigned long meas_conf = 0;
-	int ret;
+	struct hmc5843_data *data = iio_priv(indio_dev);
 
-	ret = kstrtoul(buf, 10, &meas_conf);
-	if (ret)
-		return ret;
-	if (meas_conf >= HMC5843_MEAS_CONF_MASK)
-		return -EINVAL;
+	return hmc5843_set_meas_conf(data, meas_conf);
+}
 
-	ret = hmc5843_set_meas_conf(data, meas_conf);
+static const struct iio_enum hmc5843_meas_conf_enum = {
+	.items = hmc5843_meas_conf_modes,
+	.num_items = ARRAY_SIZE(hmc5843_meas_conf_modes),
+	.get = hmc5843_show_measurement_configuration,
+	.set = hmc5843_set_measurement_configuration,
+};
 
-	return (ret < 0) ? ret : count;
-}
+static const struct iio_chan_spec_ext_info hmc5843_ext_info[] = {
+	IIO_ENUM("meas_conf", true, &hmc5843_meas_conf_enum),
+	IIO_ENUM_AVAILABLE("meas_conf", &hmc5843_meas_conf_enum),
+	{ },
+};
 
-static IIO_DEVICE_ATTR(meas_conf,
-			S_IWUSR | S_IRUGO,
-			hmc5843_show_measurement_configuration,
-			hmc5843_set_measurement_configuration,
-			0);
+static const struct iio_enum hmc5983_meas_conf_enum = {
+	.items = hmc5983_meas_conf_modes,
+	.num_items = ARRAY_SIZE(hmc5983_meas_conf_modes),
+	.get = hmc5843_show_measurement_configuration,
+	.set = hmc5843_set_measurement_configuration,
+};
+
+static const struct iio_chan_spec_ext_info hmc5983_ext_info[] = {
+	IIO_ENUM("meas_conf", true, &hmc5983_meas_conf_enum),
+	IIO_ENUM_AVAILABLE("meas_conf", &hmc5983_meas_conf_enum),
+	{ },
+};
 
 static
 ssize_t hmc5843_show_samp_freq_avail(struct device *dev,
@@ -459,6 +475,25 @@ done:
 			.storagebits = 16,				\
 			.endianness = IIO_BE,				\
 		},							\
+		.ext_info = hmc5843_ext_info,	\
+	}
+
+#define HMC5983_CHANNEL(axis, idx)					\
+	{								\
+		.type = IIO_MAGN,					\
+		.modified = 1,						\
+		.channel2 = IIO_MOD_##axis,				\
+		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),		\
+		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |	\
+			BIT(IIO_CHAN_INFO_SAMP_FREQ),			\
+		.scan_index = idx,					\
+		.scan_type = {						\
+			.sign = 's',					\
+			.realbits = 16,					\
+			.storagebits = 16,				\
+			.endianness = IIO_BE,				\
+		},							\
+		.ext_info = hmc5983_ext_info,	\
 	}
 
 static const struct iio_chan_spec hmc5843_channels[] = {
@@ -476,8 +511,14 @@ static const struct iio_chan_spec hmc5883_channels[] = {
 	IIO_CHAN_SOFT_TIMESTAMP(3),
 };
 
+static const struct iio_chan_spec hmc5983_channels[] = {
+	HMC5983_CHANNEL(X, 0),
+	HMC5983_CHANNEL(Z, 1),
+	HMC5983_CHANNEL(Y, 2),
+	IIO_CHAN_SOFT_TIMESTAMP(3),
+};
+
 static struct attribute *hmc5843_attributes[] = {
-	&iio_dev_attr_meas_conf.dev_attr.attr,
 	&iio_dev_attr_scale_available.dev_attr.attr,
 	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
 	NULL
@@ -516,7 +557,7 @@ static const struct hmc5843_chip_info hmc5843_chip_info_tbl[] = {
 				ARRAY_SIZE(hmc5883l_regval_to_nanoscale),
 	},
 	[HMC5983_ID] = {
-		.channels = hmc5883_channels,
+		.channels = hmc5983_channels,
 		.regval_to_samp_freq = hmc5983_regval_to_samp_freq,
 		.n_regval_to_samp_freq =
 				ARRAY_SIZE(hmc5983_regval_to_samp_freq),