linux-kernel - [PATCH] spi: disable chipselect after complete transfer

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Date:   Wed, 9 Feb 2022 18:00:42 +0800
From:   Yun Zhou <yun.zhou@...driver.com>
To:     <broonie@...nel.org>, <yun.zhou@...driver.com>
CC:     <linux-spi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <ying.xue@...driver.com>
Subject: [PATCH] spi: disable chipselect after complete transfer

If there are 2 slaves or more on a spi bus, e.g. A and B, we processed a
transfer to A, the CS will be selected for A whose 'last_cs_enable' will
be recorded to true at the same time. Then we processed a transfer to B,
the CS will be switched to B. And then if we transmit data to A again, it
will not enable CS back to A because 'last_cs_enable' is true.
In addition, if CS is not disabled, Some controllers in automatic
transmission state will receive unpredictable data, such as Cadence SPI
controller.

Signed-off-by: Yun Zhou <yun.zhou@...driver.com>
---
 drivers/spi/spi.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index fdd530b150a7..ebbba0b08186 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1417,7 +1417,6 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 				    struct spi_message *msg)
 {
 	struct spi_transfer *xfer;
-	bool keep_cs = false;
 	int ret = 0;
 	struct spi_statistics *statm = &ctlr->statistics;
 	struct spi_statistics *stats = &msg->spi->statistics;
@@ -1486,10 +1485,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 		spi_transfer_delay_exec(xfer);
 
 		if (xfer->cs_change) {
-			if (list_is_last(&xfer->transfer_list,
+			if (!list_is_last(&xfer->transfer_list,
 					 &msg->transfers)) {
-				keep_cs = true;
-			} else {
 				spi_set_cs(msg->spi, false, false);
 				_spi_transfer_cs_change_delay(msg, xfer);
 				spi_set_cs(msg->spi, true, false);
@@ -1500,8 +1497,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 	}
 
 out:
-	if (ret != 0 || !keep_cs)
-		spi_set_cs(msg->spi, false, false);
+	spi_set_cs(msg->spi, false, false);
 
 	if (msg->status == -EINPROGRESS)
 		msg->status = ret;
-- 
2.26.1