From: John Ogness <john.ogness@linutronix.de>
Date: Wed, 17 Apr 2024 12:13:24 +0000
Subject: [PATCH 09/46] serial: core: Introduce wrapper to set @uart_port->cons

Introduce uart_port_set_cons() as a wrapper to set @cons of a
uart_port. The wrapper sets @cons under the port lock in order
to prevent @cons from disappearing while another context is
holding the port lock. This is necessary for a follow-up
commit relating to the port lock wrappers, which rely on @cons
not changing between lock and unlock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/8250/8250_core.c |    6 +++---
 drivers/tty/serial/amba-pl011.c     |    2 +-
 drivers/tty/serial/serial_core.c    |   16 ++++++++--------
 include/linux/serial_core.h         |   17 +++++++++++++++++
 4 files changed, 29 insertions(+), 12 deletions(-)

@ drivers/tty/serial/8250/8250_core.c:630 @ static int univ8250_console_setup(struct
 
 	port = &serial8250_ports[co->index].port;
 	/* link port to console */
-	port->cons = co;
+	uart_port_set_cons(port, co);
 
 	retval = serial8250_console_setup(port, options, false);
 	if (retval != 0)
-		port->cons = NULL;
+		uart_port_set_cons(port, NULL);
 	return retval;
 }
 
@ drivers/tty/serial/8250/8250_core.c:692 @ static int univ8250_console_match(struct
 			continue;
 
 		co->index = i;
-		port->cons = co;
+		uart_port_set_cons(port, co);
 		return serial8250_console_setup(port, options, true);
 	}
 
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@ drivers/tty/serial/8250/8250_core.c:2491 @ static int pl011_console_match(struct co
 			continue;
 
 		co->index = i;
-		port->cons = co;
+		uart_port_set_cons(port, co);
 		return pl011_console_setup(co, options);
 	}
 
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@ drivers/tty/serial/8250/8250_core.c:3175 @ static int serial_core_add_one_port(stru
 	state->uart_port = uport;
 	uport->state = state;
 
+	/*
+	 * If this port is in use as a console then the spinlock is already
+	 * initialised.
+	 */
+	if (!uart_console_registered(uport))
+		uart_port_spin_lock_init(uport);
+
 	state->pm_state = UART_PM_STATE_UNDEFINED;
-	uport->cons = drv->cons;
+	uart_port_set_cons(uport, drv->cons);
 	uport->minor = drv->tty_driver->minor_start + uport->line;
 	uport->name = kasprintf(GFP_KERNEL, "%s%d", drv->dev_name,
 				drv->tty_driver->name_base + uport->line);
@ drivers/tty/serial/8250/8250_core.c:3192 @ static int serial_core_add_one_port(stru
 		goto out;
 	}
 
-	/*
-	 * If this port is in use as a console then the spinlock is already
-	 * initialised.
-	 */
-	if (!uart_console_registered(uport))
-		uart_port_spin_lock_init(uport);
-
 	if (uport->cons && uport->dev)
 		of_console_check(uport->dev->of_node, uport->cons->name, uport->line);
 
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@ drivers/tty/serial/8250/8250_core.c:613 @ static inline void __uart_port_unlock_ir
 }
 
 /**
+ * uart_port_set_cons - Safely set the @cons field for a uart
+ * @up:		The uart port to set
+ * @con:	The new console to set to
+ *
+ * This function must be used to set @up->cons. It uses the port lock to
+ * synchronize with the port lock wrappers in order to ensure that the console
+ * cannot change or disappear while another context is holding the port lock.
+ */
+static inline void uart_port_set_cons(struct uart_port *up, struct console *con)
+{
+	unsigned long flags;
+
+	__uart_port_lock_irqsave(up, &flags);
+	up->cons = con;
+	__uart_port_unlock_irqrestore(up, flags);
+}
+/**
  * uart_port_lock - Lock the UART port
  * @up:		Pointer to UART port structure
  */