[PATCH 6/6] iio: ad7949: Fix dummy read cycle placement

[Adam Michaelis <adam.michaelis@rockwellcollins.com>]

The AD7949 requires two conversion cycles following any configuration
change (including changing the analog channel being sampled). Therefore,
adding a dummy read cycle when config is changed and removing the extra
cycles at initial configuration.

Signed-off-by: Adam Michaelis <adam.michaelis@rockwellcollins.com>
---
 drivers/iio/adc/ad7949.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
index dc1ae4c143b0..4e8ad4217e5b 100644
--- a/drivers/iio/adc/ad7949.c
+++ b/drivers/iio/adc/ad7949.c
@@ -115,6 +115,25 @@ static int ad7949_spi_write_cfg(struct ad7949_adc_chip *ad7949_adc, u16 val,
 		 * time to send a new command to the device
 		 */
 		udelay(2);
+
+		/*
+		 * Perform extra read cycle to allow configuration, acquisition,
+		 * and conversion sequences to complete for new configuration.
+		 */
+		(void)memset(&tx, 0, sizeof(tx));
+		(void)memset(ad7949_adc->buffer, 0, AD7949_BUFFER_LEN);
+
+		tx.rx_buf = ad7949_adc->buffer;
+		tx.len = ad7949_spi_cfg_is_read_back(ad7949_adc) ? 4 : 2;
+
+		spi_message_init_with_transfers(&msg, &tx, 1);
+		ret = spi_sync(ad7949_adc->spi, &msg);
+
+		/*
+		 * This delay is to avoid a new request before the required time
+		 * to send a new command to the device.
+		 */
+		udelay(2);
 	}
 
 	return ret;
@@ -247,7 +266,6 @@ static int ad7949_spi_reg_access(struct iio_dev *indio_dev,
 static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 {
 	int ret;
-	int val;
 	u16 adc_config = 0;
 
 	ad7949_adc->current_channel = 0;
@@ -261,13 +279,6 @@ static int ad7949_spi_init(struct ad7949_adc_chip *ad7949_adc)
 
 	ret = ad7949_spi_write_cfg(ad7949_adc, adc_config, AD7949_MASK_TOTAL);
 
-	/*
-	 * Do two dummy conversions to apply the first configuration setting.
-	 * Required only after the start up of the device.
-	 */
-	ad7949_spi_read_channel(ad7949_adc, &val, ad7949_adc->current_channel);
-	ad7949_spi_read_channel(ad7949_adc, &val, ad7949_adc->current_channel);
-
 	return ret;
 }
 
-- 
1.9.1