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From ce0e3f83d941437f16242c8d87b3bf172eaadbd4 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 29 Sep 2017 10:32:19 +0100
Subject: [PATCH 033/194] 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(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 02275f96dbca..39d717e94af3 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1385,6 +1385,7 @@ static bool pl011_tx_char(struct uart_amba_port *uap, unsigned char c,
 		return false; /* unable to transmit character */
 
 	pl011_write(c, uap, REG_DR);
+	mb();
 	uap->port.icount.tx++;
 
 	return true;