serial: mxs-auart: fix tx

Emil reports:
  After updating Linux on an i.MX28 board, serial communication over
  AUART broke. When I TX from the board and measure on the TX pin, it
  seems like the HW fifo is not emptied before the transmission is
  stopped.

MXS performs weird things with stop_tx(). The driver makes it
conditional on uart_tx_stopped().

So the driver needs special handling. Pass the brand new UART_TX_NOSTOP
to uart_port_tx_flags() and handle the stop on its own.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Reported-by: Emil Kronborg <emil.kronborg@protonmail.com>
Cc: stable <stable@kernel.org>
Fixes: 2d141e683e9a ("tty: serial: use uart_port_tx() helper")
Closes: https://lore.kernel.org/all/miwgbnvy3hjpnricubg76ytpn7xoceehwahupy25bubbduu23s@om2lptpa26xw/
Tested-by: Stefan Wahren <wahrenst@gmx.net>
Tested-by: Emil Kronborg <emil.kronborg@protonmail.com>
Link: https://lore.kernel.org/r/20240201105557.28043-2-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c
index 3ec725555bcc1e6eb2843a186a5c49cba1ab0b42..4749331fe618cad7c0af98630f90021b8244bd07 100644 (file)
--- a/drivers/tty/serial/mxs-auart.c
+++ b/drivers/tty/serial/mxs-auart.c
@@ -605,13 +605,16 @@ static void mxs_auart_tx_chars(struct mxs_auart_port *s)
                return;
        }
 
-       pending = uart_port_tx(&s->port, ch,
+       pending = uart_port_tx_flags(&s->port, ch, UART_TX_NOSTOP,
                !(mxs_read(s, REG_STAT) & AUART_STAT_TXFF),
                mxs_write(ch, s, REG_DATA));
        if (pending)
                mxs_set(AUART_INTR_TXIEN, s, REG_INTR);
        else
                mxs_clr(AUART_INTR_TXIEN, s, REG_INTR);
+
+       if (uart_tx_stopped(&s->port))
+               mxs_auart_stop_tx(&s->port);
 }
 
 static void mxs_auart_rx_char(struct mxs_auart_port *s)