[PATCH] tty: atmel_serial: fix a NULL pointer dereference

[Kangjie Lu]

In case dmaengine_prep_dma_cyclic fails, the fix returns a proper
error code to avoid NULL pointer dereference.

Signed-off-by: Kangjie Lu <k...@umn.edu>
Fixes: 34df42f59a60 ("serial: at91: add rx dma support")

---
V2: simplified the patch as suggested by
Richard Genoud <richard.gen...@gmail.com>
---
 drivers/tty/serial/atmel_serial.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/serial/atmel_serial.c 
b/drivers/tty/serial/atmel_serial.c
index 05147fe24343..41b728d223d1 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1288,6 +1288,10 @@ static int atmel_prepare_rx_dma(struct uart_port *port)
                                         sg_dma_len(&atmel_port->sg_rx)/2,
                                         DMA_DEV_TO_MEM,
                                         DMA_PREP_INTERRUPT);
+       if (!desc) {
+               dev_err(port->dev, "Preparing DMA cyclic failed\n");
+               goto chan_err;
+       }
        desc->callback = atmel_complete_rx_dma;
        desc->callback_param = port;
        atmel_port->desc_rx = desc;
-- 
2.17.1