serial: 8250: Fix lost rx state

When max_count is reached, the rx loop exits. However, UART_LSR has
already been read so those char flags are lost, and subsequent rx
status will be for the wrong byte until the rx fifo drains.

Reported-by: George Spelvin <linux@horizon.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 7580d713cde5b0b7f24c5fc3d0aa0a0600cdca58..48680565c9914c8797fc82b6954881415ce6d128 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1478,16 +1478,17 @@ static void serial8250_read_char(struct uart_8250_port *up, unsigned char lsr)
  * value, and returns the remaining LSR bits not handled
  * by this Rx routine.
  */
-unsigned char
-serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr)
+unsigned char serial8250_rx_chars(struct uart_8250_port *up, unsigned char lsr)
 {
        struct uart_port *port = &up->port;
        int max_count = 256;
 
        do {
                serial8250_read_char(up, lsr);
+               if (--max_count == 0)
+                       break;
                lsr = serial_in(up, UART_LSR);
-       } while ((lsr & (UART_LSR_DR | UART_LSR_BI)) && (--max_count > 0));
+       } while (lsr & (UART_LSR_DR | UART_LSR_BI));
        spin_unlock(&port->lock);
        tty_flip_buffer_push(&port->state->port);
        spin_lock(&port->lock);