From: Phil Elwell <phil@raspberrypi.org>
Date: Fri, 29 Sep 2017 09:32:19 +0000 (+0100)
Subject: amba_pl011: Insert mb() for correct FIFO handling
X-Git-Tag: accepted/tizen/unified/20200709.164653~1261
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=487b679ced7c0c528c755f7b9c31fbd0bbdd8edf;p=platform%2Fkernel%2Flinux-rpi.git

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>
---

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 81a60f2..e397c37 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1383,6 +1383,7 @@ 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;