From 7e09080c4e3dd47b823e19319be6538250554b17 Mon Sep 17 00:00:00 2001
From: Amelie Delaunay <amelie.delaunay@foss.st.com>
Date: Tue, 8 Aug 2023 18:19:06 +0200
Subject: [PATCH] serial: stm32: synchronize RX DMA channel in shutdown

References: bsc#1214683 (PREEMPT_RT prerequisite backports)
Patch-mainline: v6.6-rc1
Git-commit: 2490a0ca5735714bd2ba8ba8a41fa9343b422113

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@foss.st.com>
Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
Link: https://lore.kernel.org/r/20230808161906.178996-7-valentin.caron@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 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 ca46711008ef..b6f4f436a565 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -1119,8 +1119,10 @@ 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)