[PATCH v4 05/13] iio: adc: ad4134: Run shorter transfers when CRC is disabled

[Marcelo Schmitt <marcelo.schmitt@analog.com>]

When AD4134 has its SPI CRC feature enabled, one extra byte (the CRC code)
is sent through SPI for both ends to verify the integrity of data
transfers. Though, when CRC is not enabled, SPI transfers can be shorter.

Signed-off-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
---
 drivers/iio/adc/ad4134.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/iio/adc/ad4134.c b/drivers/iio/adc/ad4134.c
index a0113fff4b71..85fa16321d74 100644
--- a/drivers/iio/adc/ad4134.c
+++ b/drivers/iio/adc/ad4134.c
@@ -106,6 +106,7 @@ struct ad4134_state {
 	 */
 	struct mutex sync_lock;
 	int refin_mv;
+	bool crc_en;
 	/*
 	 * DMA (thus cache coherency maintenance) requires the transfer buffers
 	 * to live in their own cache lines.
@@ -159,7 +160,7 @@ static int ad4134_reg_write(void *context, unsigned int reg, unsigned int val)
 	struct spi_transfer xfer = {
 		.tx_buf = st->tx_buf,
 		.rx_buf = st->rx_buf,
-		.len = AD4134_SPI_MAX_XFER_LEN,
+		.len = st->crc_en ? AD4134_SPI_MAX_XFER_LEN : 2,
 	};
 	int ret;
 
@@ -169,7 +170,7 @@ static int ad4134_reg_write(void *context, unsigned int reg, unsigned int val)
 	if (ret)
 		return ret;
 
-	if (st->rx_buf[2] != st->tx_buf[2])
+	if (st->crc_en && st->rx_buf[2] != st->tx_buf[2])
 		dev_dbg(&st->spi->dev, "reg write CRC check failed\n");
 
 	return 0;
@@ -217,7 +218,7 @@ static int ad4134_register_read(struct ad4134_state *st, unsigned int reg,
 	struct spi_transfer xfer = {
 		.tx_buf = st->tx_buf,
 		.rx_buf = st->rx_buf,
-		.len = AD4134_SPI_MAX_XFER_LEN,
+		.len = st->crc_en ? AD4134_SPI_MAX_XFER_LEN : 2,
 	};
 	unsigned int inst;
 	int ret;
@@ -232,7 +233,7 @@ static int ad4134_register_read(struct ad4134_state *st, unsigned int reg,
 	*val = st->rx_buf[1];
 
 	/* Check CRC */
-	if (st->rx_buf[2] != st->tx_buf[2])
+	if (st->crc_en && st->rx_buf[2] != st->tx_buf[2])
 		dev_dbg(&st->spi->dev, "reg read CRC check failed\n");
 
 	return 0;
@@ -313,6 +314,7 @@ static int ad4134_min_io_mode_setup(struct ad4134_state *st)
 	struct device *dev = &st->spi->dev;
 	int ret;
 
+	st->crc_en = true; /* In minimum I/O mode CRC cannot be disabled */
 	st->odr_gpio = devm_gpiod_get(dev, "odr", GPIOD_OUT_LOW);
 	if (IS_ERR(st->odr_gpio))
 		return dev_err_probe(dev, PTR_ERR(st->odr_gpio),
-- 
2.53.0