Hi,

On Tue, May 08, 2018 at 08:43:51AM +0200, Uwe Kleine-König wrote:

On Mon, May 07, 2018 at 11:36:10PM +0200, Sebastian Reichel wrote:

quoted

This properly unmaps DMA SG on device shutdown.

Reported-by: Nandor Han <redacted>
Suggested-by: Nandor Han <redacted>
Signed-off-by: Sebastian Reichel <redacted>
---
 drivers/tty/serial/imx.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 3ca767b1162a..6c53e74244ec 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c

@@ -1425,10 +1425,18 @@ static void imx_uart_shutdown(struct uart_port *port)
 	u32 ucr1, ucr2;
 
 	if (sport->dma_is_enabled) {
-		sport->dma_is_rxing = 0;
-		sport->dma_is_txing = 0;
 		dmaengine_terminate_sync(sport->dma_chan_tx);
+		if (sport->dma_is_txing) {
+			dma_unmap_sg(sport->port.dev, &sport->tx_sgl[0],
+				     sport->dma_tx_nents, DMA_TO_DEVICE);
+			sport->dma_is_txing = 0;
+		}

did you find this because the kernel crashed or consumed more and more
memory, or is this "only" a finding of reading the source code? If the
former it would be great to point out in the commit log, if the latter,
I wonder if this is a real problem that warrants a stable backport.

A bit of both. One of Collabora's customers had a (scarce) kernel crash
in imx-serial and modified multiple things in the driver. The crash is
gone, but it's not clear which change fixed it. I could not
reproduce the crash so far and I'm currently rebasing and splitting
their changes into upstreamable portions with proper patch
descriptions. From reading the source this looked like a real issue.

-- Sebastian