linux-kernel - [PATCH 5.4 01/62] iio: adc: ti-ads7950: Ensure CS is deasserted after reading channels

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Message-Id: <20210816125428.246615152@linuxfoundation.org>
Date:   Mon, 16 Aug 2021 15:01:33 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        David Lechner <david@...hnology.com>, Stable@...r.kernel.org,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: [PATCH 5.4 01/62] iio: adc: ti-ads7950: Ensure CS is deasserted after reading channels

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.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@...gutronix.de>
Reviewed-by: David Lechner <david@...hnology.com>
Tested-by: David Lechner <david@...hnology.com>
Cc: <Stable@...r.kernel.org>
Link: https://lore.kernel.org/r/20210709101110.1814294-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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
@@ -569,7 +569,6 @@ 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);