patch "serial: pch: don't overwrite xmit->buf[0] by x_char" added to tty-testing

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

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

to my tty git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty.git
in the tty-testing branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will be merged to the tty-next branch sometime soon,
after it passes testing, and the merge window is open.

If you have any questions about this process, please let me know.


From d9f3af4fbb1d955bbaf872d9e76502f6e3e803cb Mon Sep 17 00:00:00 2001
From: Jiri Slaby <jslaby@suse.cz>
Date: Tue, 3 May 2022 10:08:03 +0200
Subject: serial: pch: don't overwrite xmit->buf[0] by x_char

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>
---
 drivers/tty/serial/pch_uart.c | 27 +++++++--------------------
 1 file changed, 7 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/serial/pch_uart.c b/drivers/tty/serial/pch_uart.c
index f872613a5e83..6cb631487383 100644
--- 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--;
 	}
@@ -948,9 +933,11 @@ 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--;
 	}
 
-- 
2.36.0