iio: adc: ad7768-1: Add multiple scan types to support 16-bits mode

When the device is configured to Sinc5 filter and decimation x8,
output data is reduced to 16-bits in order to support 1 MHz of
sampling frequency due to clock limitation.

Using multiple scan types feature enables the driver to switch
scan type in runtime, making possible to support both 24-bits and
16-bits resolution.

Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>

Author: jonathanns

drivers/iio/adc/ad7768-1.c

@@ -143,6 +143,11 @@ enum ad7768_dec_rate {
 	AD7768_DEC_RATE_1024 = 5
 };
 
+enum ad7768_scan_type {
+	AD7768_SCAN_TYPE_NORMAL,
+	AD7768_SCAN_TYPE_HIGH_SPEED,
+};
+
 struct ad7768_clk_configuration {
 	enum ad7768_mclk_div mclk_div;
 	enum ad7768_dec_rate dec_rate;
@@ -199,6 +204,19 @@ static const  int sinc3_dec_rate_max_values[4] = {
 	20480, 40960, 81920, 163840,
 };
 
+static const struct iio_scan_type ad7768_scan_type[] = {
+	[AD7768_SCAN_TYPE_NORMAL] = {
+		.sign = 's',
+		.realbits = 24,
+		.storagebits = 32,
+	},
+	[AD7768_SCAN_TYPE_HIGH_SPEED] = {
+		.sign = 's',
+		.realbits = 16,
+		.storagebits = 32,
+	},
+};
+
 static const char * const ad7768_filter_enum[] = {
 	[SINC5] = "sinc5",
 	[SINC5_DEC_X8] = "sinc5-dec8",
@@ -270,12 +288,9 @@ static const struct iio_chan_spec ad7768_channels[] = {
 		.indexed = 1,
 		.channel = 0,
 		.scan_index = 0,
-		.scan_type = {
-			.sign = 's',
-			.realbits = 24,
-			.storagebits = 32,
-			.shift = 8,
-		},
+		.has_ext_scan_type = 1,
+		.ext_scan_type = ad7768_scan_type,
+		.num_ext_scan_type = ARRAY_SIZE(ad7768_scan_type),
 	},
 };
 
@@ -424,6 +439,9 @@ static int ad7768_scan_direct(struct iio_dev *indio_dev)
 	ret = ad7768_spi_reg_read(st, AD7768_REG_ADC_DATA, &readval, 3);
 	if (ret < 0)
 		return ret;
+
+	if (st->filter_mode == SINC5_DEC_X8)
+		readval = readval >> 8;
 	/*
 	 * Any SPI configuration of the AD7768-1 can only be
 	 * performed in continuous conversion mode.
@@ -825,6 +843,11 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 {
 	struct ad7768_state *st = iio_priv(indio_dev);
 	int scale_uv, ret;
+	const struct iio_scan_type *scan_type;
+
+	scan_type = iio_get_current_scan_type(indio_dev, chan);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
 
 	switch (info) {
 	case IIO_CHAN_INFO_RAW:
@@ -834,7 +857,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 
 		ret = ad7768_scan_direct(indio_dev);
 		if (ret >= 0)
-			*val = sign_extend32(ret, chan->scan_type.realbits - 1);
+			*val = sign_extend32(ret, scan_type->realbits - 1);
 
 		iio_device_release_direct_mode(indio_dev);
 		if (ret < 0)
@@ -848,7 +871,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
 			return scale_uv;
 
 		*val = (scale_uv * 2) / 1000;
-		*val2 = chan->scan_type.realbits;
+		*val2 = scan_type->realbits;
 
 		return IIO_VAL_FRACTIONAL_LOG2;
 
@@ -892,11 +915,21 @@ static const struct attribute_group ad7768_group = {
 	.attrs = ad7768_attributes,
 };
 
+static int ad7768_get_current_scan_type(const struct iio_dev *indio_dev,
+					const struct iio_chan_spec *chan)
+{
+	struct ad7768_state *st = iio_priv(indio_dev);
+
+	return st->filter_mode == SINC5_DEC_X8 ? AD7768_SCAN_TYPE_HIGH_SPEED
+					    : AD7768_SCAN_TYPE_NORMAL;
+}
+
 static const struct iio_info ad7768_info = {
 	.attrs = &ad7768_group,
 	.read_raw = &ad7768_read_raw,
 	.write_raw = &ad7768_write_raw,
 	.read_label = ad7768_read_label,
+	.get_current_scan_type = &ad7768_get_current_scan_type,
 	.debugfs_reg_access = &ad7768_reg_access,
 };
 
@@ -1009,13 +1042,18 @@ static int ad7768_buffer_postenable(struct iio_dev *indio_dev)
 	struct ad7768_state *st = iio_priv(indio_dev);
 	struct spi_transfer xfer = {
 		.len = 1,
-		.bits_per_word = 32
 	};
 	unsigned int rx_data[2];
-	unsigned int tx_data[2];
 	struct spi_message msg;
+	const struct iio_scan_type *scan_type;
 	int ret;
 
+	scan_type = iio_get_current_scan_type(indio_dev, &indio_dev->channels[0]);
+	if (IS_ERR(scan_type))
+		return PTR_ERR(scan_type);
+
+	xfer.bits_per_word = scan_type->realbits;
+
 	/*
 	* Write a 1 to the LSB of the INTERFACE_FORMAT register to enter
 	* continuous read mode. Subsequent data reads do not require an
@@ -1028,8 +1066,6 @@ static int ad7768_buffer_postenable(struct iio_dev *indio_dev)
 	if (st->spi_is_dma_mapped) {
 		spi_bus_lock(st->spi->master);
 
-		tx_data[0] = AD7768_RD_FLAG_MSK(AD7768_REG_ADC_DATA) << 24;
-		xfer.tx_buf = tx_data;
 		xfer.rx_buf = rx_data;
 		spi_message_init_with_transfers(&msg, &xfer, 1);
 		ret = spi_engine_offload_load_msg(st->spi, &msg);