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Subject[PATCH 4.4 048/190] serial: sh-sci: Fix race condition causing garbage during shutdown
Date
4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Geert Uytterhoeven <geert+renesas@glider.be>


[ Upstream commit 1cf4a7efdc71cab84c42cfea7200608711ea954f ]

If DMA is enabled and used, a burst of old data may be seen on the
serial console during "poweroff" or "reboot". uart_flush_buffer()
clears the circular buffer, but sci_port.tx_dma_len is not reset.
This leads to a circular buffer overflow, dumping (UART_XMIT_SIZE -
sci_port.tx_dma_len) bytes.

To fix this, add a .flush_buffer() callback that resets
sci_port.tx_dma_len.

Inspired by commit 31ca2c63fdc0aee7 ("tty/serial: atmel: fix race
condition (TX+DMA)").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/tty/serial/sh-sci.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1457,7 +1457,16 @@ static void sci_free_dma(struct uart_por
if (s->chan_rx)
sci_rx_dma_release(s, false);
}
-#else
+
+static void sci_flush_buffer(struct uart_port *port)
+{
+ /*
+ * In uart_flush_buffer(), the xmit circular buffer has just been
+ * cleared, so we have to reset tx_dma_len accordingly.
+ */
+ to_sci_port(port)->tx_dma_len = 0;
+}
+#else /* !CONFIG_SERIAL_SH_SCI_DMA */
static inline void sci_request_dma(struct uart_port *port)
{
}
@@ -1465,7 +1474,9 @@ static inline void sci_request_dma(struc
static inline void sci_free_dma(struct uart_port *port)
{
}
-#endif
+
+#define sci_flush_buffer NULL
+#endif /* !CONFIG_SERIAL_SH_SCI_DMA */

static irqreturn_t sci_rx_interrupt(int irq, void *ptr)
{
@@ -2205,6 +2216,7 @@ static struct uart_ops sci_uart_ops = {
.break_ctl = sci_break_ctl,
.startup = sci_startup,
.shutdown = sci_shutdown,
+ .flush_buffer = sci_flush_buffer,
.set_termios = sci_set_termios,
.pm = sci_pm,
.type = sci_type,

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