From 37e06c9ed7219cf6cf08a0463f7e2b5b2c51f3e6 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 29 Sep 2017 10:32:19 +0100
Subject: [PATCH] amba_pl011: Insert mb() for correct FIFO handling

The pl011 register accessor functions use the _relaxed versions of the
standard readl() and writel() functions, meaning that there are no
automatic memory barriers. When polling a FIFO status register to check
for fullness, it is necessary to ensure that any outstanding writes have
completed; otherwise the flags are effectively stale, making it possible
that the next write is to a full FIFO.

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 drivers/tty/serial/amba-pl011.c | 1 +
 1 file changed, 1 insertion(+)

--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1386,6 +1386,7 @@ static bool pl011_tx_char(struct uart_am
 		return false; /* unable to transmit character */
 
 	pl011_write(c, uap, REG_DR);
+	mb();
 	uap->port.icount.tx++;
 
 	return true;
