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iio: adc: ti-ads7950: Ensure CS is deasserted after reading channels

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The ADS7950 requires that CS is deasserted after each SPI word. Before
commit e2540da86e ("iio: adc: ti-ads7950: use SPI_CS_WORD to reduce
CPU usage") the driver used a message with one spi transfer per channel
where each but the last one had .cs_change set to enforce a CS toggle.
This was wrongly translated into a message with a single transfer and
.cs_change set which results in a CS toggle after each word but the
last which corrupts the first adc conversion of all readouts after the
first readout.

Fixes: e2540da86e ("iio: adc: ti-ads7950: use SPI_CS_WORD to reduce CPU usage")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: David Lechner <david@lechnology.com>
Tested-by: David Lechner <david@lechnology.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210709101110.1814294-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Uwe Kleine-König 2021-07-09 12:11:10 +02:00 committed by Jonathan Cameron
parent 4377d9ab1f
commit 9898cb24e4
1 changed files with 0 additions and 1 deletions
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drivers/iio/adc/ti-ads7950.c
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@ -568,7 +568,6 @@ static int ti_ads7950_probe(struct spi_device *spi)
st->ring_xfer.tx_buf = &st->tx_buf[0];
st->ring_xfer.rx_buf = &st->rx_buf[0];
/* len will be set later */
st->ring_xfer.cs_change = true;
spi_message_add_tail(&st->ring_xfer, &st->ring_msg);