[PATCH] tty: serial: msm: Don't read off end of tx fifo

[Bjorn Andersson]

For dm uarts in pio mode tx data is transferred to the fifo register 4
bytes at a time, but care is not taken when these 4 bytes spans the end
of the xmit buffer so the loop might read up to 3 bytes past the buffer
and then skip the actual data at the beginning of the buffer.

Fix this by, analogous to the DMA case, make sure the chunk doesn't
wrap the xmit buffer.

Fixes: 3a878c430fd6 ("tty: serial: msm: Add TX DMA support")
Cc: Andy Gross <andy.gross@xxxxxxxxxx>
Cc: Ivan Ivanov <iivanov.xz@xxxxxxxxx>
Cc: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reported-by: Frank Rowand <frowand.list@xxxxxxxxx>
Reported-by: Nicolas Dechesne <nicolas.dechesne@xxxxxxxxxx>
Signed-off-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>
---
 drivers/tty/serial/msm_serial.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
index b7d80bd57db9..7d62610d9de5 100644
--- a/drivers/tty/serial/msm_serial.c
+++ b/drivers/tty/serial/msm_serial.c
@@ -726,7 +726,7 @@ static void msm_handle_tx(struct uart_port *port)
 		return;
 	}
 
-	pio_count = CIRC_CNT(xmit->head, xmit->tail, UART_XMIT_SIZE);
+	pio_count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
 	dma_count = CIRC_CNT_TO_END(xmit->head, xmit->tail, UART_XMIT_SIZE);
 
 	dma_min = 1;	/* Always DMA */
-- 
2.5.0