serial: pch: don't overwrite xmit->buf[0] by x_char

commit d9f3af4fbb1d955bbaf872d9e76502f6e3e803cb upstream.

When x_char is to be sent, the TX path overwrites whatever is in the
circular buffer at offset 0 with x_char and sends it using
pch_uart_hal_write(). I don't understand how this was supposed to work
if xmit->buf[0] already contained some character. It must have been
lost.

Remove this whole pop_tx_x() concept and do the work directly in the
callers. (Without printing anything using dev_dbg().)

Cc: <stable@vger.kernel.org>
Fixes: 3c6a483275f4 (Serial: EG20T: add PCH_UART driver)
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220503080808.28332-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index f0351e6..1e65933 100644 (file)
--- a/drivers/tty/serial/pch_uart.c
+++ b/drivers/tty/serial/pch_uart.c
@@ -624,22 +624,6 @@ static int push_rx(struct eg20t_port *priv, const unsigned char *buf,
        return 0;
 }
 
-static int pop_tx_x(struct eg20t_port *priv, unsigned char *buf)
-{
-       int ret = 0;
-       struct uart_port *port = &priv->port;
-
-       if (port->x_char) {
-               dev_dbg(priv->port.dev, "%s:X character send %02x (%lu)\n",
-                       __func__, port->x_char, jiffies);
-               buf[0] = port->x_char;
-               port->x_char = 0;
-               ret = 1;
-       }
-
-       return ret;
-}
-
 static int dma_push_rx(struct eg20t_port *priv, int size)
 {
        int room;
@@ -889,9 +873,10 @@ static unsigned int handle_tx(struct eg20t_port *priv)
 
        fifo_size = max(priv->fifo_size, 1);
        tx_empty = 1;
-       if (pop_tx_x(priv, xmit->buf)) {
-               pch_uart_hal_write(priv, xmit->buf, 1);
+       if (port->x_char) {
+               pch_uart_hal_write(priv, &port->x_char, 1);
                port->icount.tx++;
+               port->x_char = 0;
                tx_empty = 0;
                fifo_size--;
        }
@@ -946,9 +931,11 @@ static unsigned int dma_handle_tx(struct eg20t_port *priv)
        }
 
        fifo_size = max(priv->fifo_size, 1);
-       if (pop_tx_x(priv, xmit->buf)) {
-               pch_uart_hal_write(priv, xmit->buf, 1);
+
+       if (port->x_char) {
+               pch_uart_hal_write(priv, &port->x_char, 1);
                port->icount.tx++;
+               port->x_char = 0;
                fifo_size--;
        }