From: John Ogness <john.ogness@linutronix.de>
Date: Mon, 11 Dec 2023 09:19:18 +0000
Subject: [PATCH 130/134] serial: core: Provide low-level functions to port
 lock
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz

The nbcon console's driver_enter() and driver_exit() callbacks need
to lock the port lock in order to synchronize against other hardware
activity (such as adjusting baud rates). However, they cannot use
the uart_port_lock() wrappers because the printk subsystem will
perform nbcon locking after calling the driver_enter() callback.

Provide low-level variants __uart_port_lock_irqsave() and
__uart_port_unlock_irqrestore() for this purpose. These are only
to be used by the driver_enter()/driver_exit() callbacks.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/serial_core.h |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -681,6 +681,18 @@ static inline void uart_port_unlock_irqr
 	spin_unlock_irqrestore(&up->lock, flags);
 }
 
+/* Only for use in the console->driver_enter() callback. */
+static inline void __uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags)
+{
+	spin_lock_irqsave(&up->lock, *flags);
+}
+
+/* Only for use in the console->driver_exit() callback. */
+static inline void __uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags)
+{
+	spin_unlock_irqrestore(&up->lock, flags);
+}
+
 static inline int serial_port_in(struct uart_port *up, int offset)
 {
 	return up->serial_in(up, offset);
