Subject: [PATCH 03/18] serial: bcm63xx: Use uart_prepare_sysrq_char().
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 1 Mar 2024 22:45:16 +0100

The port lock is a spinlock_t which is becomes a sleeping lock on PREEMPT_RT.
The driver splits the locking function into two parts: local_irq_save() and
uart_port_lock() and this breaks PREEMPT_RT.

Delay handling sysrq until port lock is dropped.
Remove the special case in the console write routine an always use the
complete locking function.

Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 drivers/tty/serial/bcm63xx_uart.c |   24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/bcm63xx_uart.c
===================================================================
--- linux-6.8.2-rt10.orig/drivers/tty/serial/bcm63xx_uart.c
+++ linux-6.8.2-rt10/drivers/tty/serial/bcm63xx_uart.c
@@ -285,10 +285,9 @@ static void bcm_uart_do_rx(struct uart_p
 				flag = TTY_PARITY;
 		}
 
-		if (uart_handle_sysrq_char(port, c))
+		if (uart_prepare_sysrq_char(port, c))
 			continue;
 
-
 		if ((cstat & port->ignore_status_mask) == 0)
 			tty_insert_flip_char(tty_port, c, flag);
 
@@ -353,7 +352,7 @@ static irqreturn_t bcm_uart_interrupt(in
 					       estat & UART_EXTINP_DCD_MASK);
 	}
 
-	uart_port_unlock(port);
+	uart_unlock_and_check_sysrq(port);
 	return IRQ_HANDLED;
 }
 
@@ -703,20 +702,14 @@ static void bcm_console_write(struct con
 {
 	struct uart_port *port;
 	unsigned long flags;
-	int locked;
+	int locked = 1;
 
 	port = &ports[co->index];
 
-	local_irq_save(flags);
-	if (port->sysrq) {
-		/* bcm_uart_interrupt() already took the lock */
-		locked = 0;
-	} else if (oops_in_progress) {
-		locked = uart_port_trylock(port);
-	} else {
-		uart_port_lock(port);
-		locked = 1;
-	}
+	if (oops_in_progress)
+		locked = uart_port_trylock_irqsave(port, &flags);
+	else
+		uart_port_lock_irqsave(port, &flags);
 
 	/* call helper to deal with \r\n */
 	uart_console_write(port, s, count, bcm_console_putchar);
@@ -725,8 +718,7 @@ static void bcm_console_write(struct con
 	wait_for_xmitr(port);
 
 	if (locked)
-		uart_port_unlock(port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(port, flags);
 }
 
 /*