pch_uart: Fix dma channel unallocated issue

This driver anticipates pch_uart_verify_port() is not called
during installation.
However, actually pch_uart_verify_port() is called during
installation.
As a result, memory access violation occurs like below.

0. initial value: use_dma=0
1. starup()
    - dma channel is not allocated because use_dma=0
2. pch_uart_verify_port()
    - Set use_dma=1
3. UART processing acts DMA mode because use_dma=1
     - memory access violation occurs!

This patch fixes the issue.

Solution:
Whenever pch_uart_verify_port() is called and then
dma channel is not allocated, the channel should be allocated.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index bbbec4a74cfb..c2816f494807 100644
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -1447,9 +1447,11 @@ static int pch_uart_verify_port(struct uart_port *port,
                         __func__);
                 return -EOPNOTSUPP;
 #endif
-                priv->use_dma = 1;
                 priv->use_dma_flag = 1;
                 dev_info(priv->port.dev, "PCH UART : Use DMA Mode\n");
+                if (!priv->use_dma)
+                        pch_request_dma(port);
+                priv->use_dma = 1;
         }
 
         return 0;