[PATCH v4 1/7] serial: 8250: Protect LCR write in shutdown

["Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>]

The 8250_dw driver needs to potentially perform very complex operations
during LCR writes because its BUSY handling prevents updates to LCR
while UART is BUSY (which is not fully under our control without those
complex operations). Thus, LCR writes should occur under port's lock.

Move LCR write under port's lock in serial8250_do_shutdown(). Also
split the LCR RMW so that the logic is on a separate line for clarity.

Reported-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Bandal, Shankar" <shankar.bandal@intel.com>
Tested-by: "Murthy, Shanth" <shanth.murthy@intel.com>
Cc: stable@vger.kernel.org
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
---
 drivers/tty/serial/8250/8250_port.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 719faf92aa8a..f7a3c5555204 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2350,6 +2350,7 @@ static int serial8250_startup(struct uart_port *port)
 void serial8250_do_shutdown(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
+	u32 lcr;
 
 	serial8250_rpm_get(up);
 	/*
@@ -2376,13 +2377,13 @@ void serial8250_do_shutdown(struct uart_port *port)
 			port->mctrl &= ~TIOCM_OUT2;
 
 		serial8250_set_mctrl(port, port->mctrl);
+
+		/* Disable break condition */
+		lcr = serial_port_in(port, UART_LCR);
+		lcr &= ~UART_LCR_SBC;
+		serial_port_out(port, UART_LCR, lcr);
 	}
 
-	/*
-	 * Disable break condition and FIFOs
-	 */
-	serial_port_out(port, UART_LCR,
-			serial_port_in(port, UART_LCR) & ~UART_LCR_SBC);
 	serial8250_clear_fifos(up);
 
 	rsa_disable(up);
-- 
2.39.5