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    Subject[PATCH 5.13 003/151] iio: adc: ti-ads7950: Ensure CS is deasserted after reading channels
    Date
    From: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

    commit 9898cb24e454602beb6e17bacf9f97b26c85c955 upstream.

    The ADS7950 requires that CS is deasserted after each SPI word. Before
    commit e2540da86ef8 ("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: e2540da86ef8 ("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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/iio/adc/ti-ads7950.c | 1 -
    1 file changed, 1 deletion(-)

    --- a/drivers/iio/adc/ti-ads7950.c
    +++ b/drivers/iio/adc/ti-ads7950.c
    @@ -568,7 +568,6 @@ static int ti_ads7950_probe(struct spi_d
    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);


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