iio: accel: sca3300: Add interface for operation modes.

The acceleration scale and the frequency were set via operation modes,
the scal and frequency are both non-uniqueness,
this leads to logic confusion for setting scale.and.frequency.
it getting worse if add more different sensor types into the driver.

The commit add an interface for set and get the operation modes.
the following interfaces added:
in_accel_op_mode_available
in_op_mode

SCA3300 operation modes table:
| Mode | Full-scale | low pass filter frequency |
| ---- | ---------- | ------------------------- |
| 1    | ± 3 g      | 70 Hz                     |
| 2    | ± 6 g      | 70 Hz                     |
| 3    | ± 1.5 g    | 70 Hz                     |
| 4    | ± 1.5 g    | 10 Hz                     |

Signed-off-by: LI Qingwu <Qing-wu.Li@leica-geosystems.com.cn>

drivers/iio/accel/sca3300.c

@@ -42,6 +42,38 @@
 /* Device return status and mask */
 #define SCA3300_VALUE_RS_ERROR	0x3
 #define SCA3300_MASK_RS_STATUS	GENMASK(1, 0)
+enum sca3300_op_mode_indexes {
+	OP_MOD_1 = 0,
+	OP_MOD_2,
+	OP_MOD_3,
+	OP_MOD_4,
+	OP_MOD_CNT
+};
+
+static const char * const sca3300_op_modes[] = {
+	[OP_MOD_1] = "1",
+	[OP_MOD_2] = "2",
+	[OP_MOD_3] = "3",
+	[OP_MOD_4] = "4"
+};
+
+static int sca3300_get_op_mode(struct iio_dev *indio_dev,
+		const struct iio_chan_spec *chan);
+static int sca3300_set_op_mode(struct iio_dev *indio_dev,
+		const struct iio_chan_spec *chan, unsigned int mode);
+
+static const struct iio_enum sca3300_op_mode_enum = {
+	.items = sca3300_op_modes,
+	.num_items = ARRAY_SIZE(sca3300_op_modes),
+	.get = sca3300_get_op_mode,
+	.set = sca3300_set_op_mode,
+};
+
+static const struct iio_chan_spec_ext_info sca3300_ext_info[] = {
+	IIO_ENUM("op_mode", IIO_SHARED_BY_DIR, &sca3300_op_mode_enum),
+	IIO_ENUM_AVAILABLE("op_mode", &sca3300_op_mode_enum),
+	{ }
+};
 
 enum sca3300_scan_indexes {
 	SCA3300_ACC_X = 0,
@@ -70,6 +102,7 @@ enum sca3300_scan_indexes {
 		.storagebits = 16,					\
 		.endianness = IIO_CPU,					\
 	},								\
+	.ext_info = sca3300_ext_info,					\
 }
 
 #define SCA3300_TEMP_CHANNEL(index, reg) {				\
@@ -400,6 +433,28 @@ static int sca3300_read_avail(struct iio_dev *indio_dev,
 	}
 }
 
+static int sca3300_get_op_mode(struct iio_dev *indio_dev,
+		const struct iio_chan_spec *chan)
+{
+	int mode;
+	int ret;
+	struct sca3300_data *data = iio_priv(indio_dev);
+
+	ret = sca3300_read_reg(data, SCA3300_REG_MODE, &mode);
+	if (ret)
+		return ret;
+	return mode;
+
+}
+
+static int sca3300_set_op_mode(struct iio_dev *indio_dev,
+		const struct iio_chan_spec *chan, unsigned int mode)
+{
+	struct sca3300_data *data = iio_priv(indio_dev);
+
+	return sca3300_write_reg(data, SCA3300_REG_MODE, mode);
+}
+
 static const struct iio_info sca3300_info = {
 	.read_raw = sca3300_read_raw,
 	.write_raw = sca3300_write_raw,