linux-kernel - [PATCH v2 6/6] serial: stm32: synchronize RX DMA channel in shutdown

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Date:   Tue, 8 Aug 2023 18:19:06 +0200
From:   Valentin Caron <valentin.caron@...s.st.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Jiri Slaby <jirislaby@...nel.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Amelie Delaunay <amelie.delaunay@...s.st.com>,
        <linux-serial@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Valentin Caron <valentin.caron@...s.st.com>
Subject: [PATCH v2 6/6] serial: stm32: synchronize RX DMA channel in shutdown

From: Amelie Delaunay <amelie.delaunay@...s.st.com>

In shutdown, RX DMA channel is terminated. If the DMA RX callback is
scheduled but not yet executed, while a new RX DMA transfer is started, the
callback can be executed, and then disturb the ongoing RX DMA transfer.
To avoid such a case, call dmaengine_synchronize in shutdown, after the
DMA RX channel is terminated.

Signed-off-by: Amelie Delaunay <amelie.delaunay@...s.st.com>
Signed-off-by: Valentin Caron <valentin.caron@...s.st.com>
---
 drivers/tty/serial/stm32-usart.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 8fc0526be898..5e9cf0c48813 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1123,8 +1123,10 @@ static void stm32_usart_shutdown(struct uart_port *port)
 		dev_err(port->dev, "Transmission is not complete\n");
 
 	/* Disable RX DMA. */
-	if (stm32_port->rx_ch)
+	if (stm32_port->rx_ch) {
 		stm32_usart_rx_dma_terminate(stm32_port);
+		dmaengine_synchronize(stm32_port->rx_ch);
+	}
 
 	/* flush RX & TX FIFO */
 	if (ofs->rqr != UNDEF_REG)
-- 
2.25.1