Subject: [PATCH 09/18] serial: lpc32xx_hs: Use uart_prepare_sysrq_char() to handle sysrq.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 1 Mar 2024 22:45:22 +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.

Handle sysrq requests sysrq once the port lock is dropped.
Remove the special case in the console write routine an always use the
complete locking function.

Cc: Vladimir Zapolskiy <[email-masked]>
Cc: [email-masked]
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 drivers/tty/serial/lpc32xx_hs.c |   17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/lpc32xx_hs.c
===================================================================
--- linux-6.8.2-rt10.orig/drivers/tty/serial/lpc32xx_hs.c
+++ linux-6.8.2-rt10/drivers/tty/serial/lpc32xx_hs.c
@@ -136,20 +136,16 @@ static void lpc32xx_hsuart_console_write
 	int locked = 1;
 
 	touch_nmi_watchdog();
-	local_irq_save(flags);
-	if (up->port.sysrq)
-		locked = 0;
-	else if (oops_in_progress)
-		locked = uart_port_trylock(&up->port);
+	if (oops_in_progress)
+		locked = uart_port_trylock_irqsave(&up->port, &flags);
 	else
-		uart_port_lock(&up->port);
+		uart_port_lock_irqsave(&up->port, &flags);
 
 	uart_console_write(&up->port, s, count, lpc32xx_hsuart_console_putchar);
 	wait_for_xmit_empty(&up->port);
 
 	if (locked)
-		uart_port_unlock(&up->port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&up->port, flags);
 }
 
 static int __init lpc32xx_hsuart_console_setup(struct console *co,
@@ -268,7 +264,8 @@ static void __serial_lpc32xx_rx(struct u
 			tty_insert_flip_char(tport, 0, TTY_FRAME);
 		}
 
-		tty_insert_flip_char(tport, (tmp & 0xFF), flag);
+		if (!uart_prepare_sysrq_char(port, tmp & 0xff))
+			tty_insert_flip_char(tport, (tmp & 0xFF), flag);
 
 		tmp = readl(LPC32XX_HSUART_FIFO(port->membase));
 	}
@@ -333,7 +330,7 @@ static irqreturn_t serial_lpc32xx_interr
 		__serial_lpc32xx_tx(port);
 	}
 
-	uart_port_unlock(port);
+	uart_unlock_and_check_sysrq(port);
 
 	return IRQ_HANDLED;
 }