target/linux/brcm2708/patches-4.14/950-0121-amba_pl011-Insert-mb-for-correct-FIFO-handling.patch

   1 From 436e9b301802720c0bf0f080301263c6e926d723 Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.org>
   3 Date: Fri, 29 Sep 2017 10:32:19 +0100
   4 Subject: [PATCH 121/454] amba_pl011: Insert mb() for correct FIFO handling
   5
   6 The pl011 register accessor functions use the _relaxed versions of the
   7 standard readl() and writel() functions, meaning that there are no
   8 automatic memory barriers. When polling a FIFO status register to check
   9 for fullness, it is necessary to ensure that any outstanding writes have
  10 completed; otherwise the flags are effectively stale, making it possible
  11 that the next write is to a full FIFO.
  12
  13 Signed-off-by: Phil Elwell <phil@raspberrypi.org>
  14 ---
  15  drivers/tty/serial/amba-pl011.c | 1 +
  16  1 file changed, 1 insertion(+)
  17
  18 --- a/drivers/tty/serial/amba-pl011.c
  19 +++ b/drivers/tty/serial/amba-pl011.c
  20 @@ -1403,6 +1403,7 @@ static bool pl011_tx_char(struct uart_am
  21                 return false; /* unable to transmit character */
  22
  23         pl011_write(c, uap, REG_DR);
  24 +       mb();
  25         uap->port.icount.tx++;
  26
  27         return true;