[PATCH 6.12.y 3/8] serial: 8250: Protect LCR write in shutdown

["Ionut Nechita (Wind River)" <ionut.nechita@windriver.com>]

From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

commit 59a33d83bbe6d73d2071d7ae21590b29faed0503 upstream.

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 <stable@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://patch.msgid.link/20260203171049.4353-2-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[Ionut: adapt to 6.12.y - keep both 'unsigned long flags' and the
 new 'u32 lcr' declaration; place the LCR RMW inside the existing
 explicit uart_port_lock_irqsave/unlock_irqrestore region rather
 than the scoped_guard() block used upstream (cleanup-based
 uart_port_lock_irqsave guard class is not present in 6.12.y).]
Signed-off-by: Ionut Nechita <ionut.nechita@windriver.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 b4c8388ea6fc..d0f2e634ac30 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2462,6 +2462,7 @@ void serial8250_do_shutdown(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 	unsigned long flags;
+	u32 lcr;
 
 	serial8250_rpm_get(up);
 	/*
@@ -2488,13 +2489,13 @@ 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);
 	uart_port_unlock_irqrestore(port, flags);
 
-	/*
-	 * Disable break condition and FIFOs
-	 */
-	serial_port_out(port, UART_LCR,
-			serial_port_in(port, UART_LCR) & ~UART_LCR_SBC);
 	serial8250_clear_fifos(up);
 
 #ifdef CONFIG_SERIAL_8250_RSA
-- 
2.54.0