[PATCH 4/4] tty/serial: at91: reset rx_ring when port is shutdown

[Nicolas Ferre]

From: Mark Deneen <mdeneen at gmail.com>

When using RX DMA, the driver won't pass any data to the uart layer
until the buffer is flipped. When the port is shutdown, the dma buffers
are unmapped, but the head and tail of the ring buffer are not reseted.
Since the serial console will keep the port open, this will only
present itself when the uart is not shared.

To reproduce the issue, with an unpatched driver, run a getty on /dev/ttyS0
with no serial console and exit. Getty will exit, and when the new one returns
you will be unable to log in.  If you hold down a key long enough to fill the
DMA buffer and flip it, you can then log in.

Signed-off-by: Mark Deneen <mdeneen at gmail.com>
Acked-by: Leilei Zhao <leilei.zhao at atmel.com>
[nicolas.ferre at atmel.com: adapt to mainline kernel, handle !DMA case]
Cc: <stable at vger.kernel.org> # v3.12
Signed-off-by: Nicolas Ferre <nicolas.ferre at atmel.com>
---
 drivers/tty/serial/atmel_serial.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index 6e68486c83cb..2d925455c1ec 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1681,6 +1681,12 @@ static void atmel_shutdown(struct uart_port *port)
 		atmel_port->release_tx(port);
 
 	/*
+	 * Reset ring buffer pointers
+	 */
+	atmel_port->rx_ring.head = 0;
+	atmel_port->rx_ring.tail = 0;
+
+	/*
 	 * Free the interrupt
 	 */
 	free_irq(port->irq, port);
-- 
1.8.2.2