tty: serial: msm_serial: Fix XON/XOFF [Linux 5.2]

tty: serial: msm_serial: Fix XON/XOFF [Linux 5.2]

This Linux kernel change "tty: serial: msm_serial: Fix XON/XOFF" is included in the Linux 5.2 release. This change is authored by Jorge Ramirez-Ortiz <jorge.ramirez-ortiz [at] linaro.org> on Mon May 20 20:38:48 2019 +0200. The commit for this change in Linux stable tree is 61c0e37 (patch).

tty: serial: msm_serial: Fix XON/XOFF

When the tty layer requests the uart to throttle, the current code
executing in msm_serial will trigger "Bad mode in Error Handler" and
generate an invalid stack frame in pstore before rebooting (that is if
pstore is indeed configured: otherwise the user shall just notice a
reboot with no further information dumped to the console).

This patch replaces the PIO byte accessor with the word accessor
already used in PIO mode.

Fixes: 68252424a7c7 ("tty: serial: msm: Support big-endian CPUs")
Cc: [email protected]
Signed-off-by: Jorge Ramirez-Ortiz <[email protected]>
Reviewed-by: Bjorn Andersson <[email protected]>
Reviewed-by: Stephen Boyd <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

There are 5 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/tty/serial/msm_serial.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
index 1090960..23833ad 100644
--- a/drivers/tty/serial/msm_serial.c
+++ b/drivers/tty/serial/msm_serial.c
@@ -860,6 +860,7 @@ static void msm_handle_tx(struct uart_port *port)
    struct circ_buf *xmit = &msm_port->uart.state->xmit;
    struct msm_dma *dma = &msm_port->tx_dma;
    unsigned int pio_count, dma_count, dma_min;
+   char buf[4] = { 0 };
    void __iomem *tf;
    int err = 0;

@@ -869,10 +870,12 @@ static void msm_handle_tx(struct uart_port *port)
        else
            tf = port->membase + UART_TF;

+       buf[0] = port->x_char;
+
        if (msm_port->is_uartdm)
            msm_reset_dm_count(port, 1);

-       iowrite8_rep(tf, &port->x_char, 1);
+       iowrite32_rep(tf, buf, 1);
        port->icount.tx++;
        port->x_char = 0;
        return;

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