Subject: [PATCH 12/18] serial: sifive: Use uart_prepare_sysrq_char() to handle sysrq.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 1 Mar 2024 22:45:25 +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: Palmer Dabbelt <[email-masked]>
Cc: Paul Walmsley <[email-masked]>
Cc: [email-masked]
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 drivers/tty/serial/sifive.c |   17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/sifive.c
===================================================================
--- linux-6.8.2-rt10.orig/drivers/tty/serial/sifive.c
+++ linux-6.8.2-rt10/drivers/tty/serial/sifive.c
@@ -412,7 +412,8 @@ static void __ssp_receive_chars(struct s
 			break;
 
 		ssp->port.icount.rx++;
-		uart_insert_char(&ssp->port, 0, 0, ch, TTY_NORMAL);
+		if (!uart_prepare_sysrq_char(&ssp->port, ch))
+			uart_insert_char(&ssp->port, 0, 0, ch, TTY_NORMAL);
 	}
 
 	tty_flip_buffer_push(&ssp->port.state->port);
@@ -534,7 +535,7 @@ static irqreturn_t sifive_serial_irq(int
 	if (ip & SIFIVE_SERIAL_IP_TXWM_MASK)
 		__ssp_transmit_chars(ssp);
 
-	uart_port_unlock(&ssp->port);
+	uart_unlock_and_check_sysrq(&ssp->port);
 
 	return IRQ_HANDLED;
 }
@@ -791,13 +792,10 @@ static void sifive_serial_console_write(
 	if (!ssp)
 		return;
 
-	local_irq_save(flags);
-	if (ssp->port.sysrq)
-		locked = 0;
-	else if (oops_in_progress)
-		locked = uart_port_trylock(&ssp->port);
+	if (oops_in_progress)
+		locked = uart_port_trylock_irqsave(&ssp->port, &flags);
 	else
-		uart_port_lock(&ssp->port);
+		uart_port_lock_irqsave(&ssp->port, &flags);
 
 	ier = __ssp_readl(ssp, SIFIVE_SERIAL_IE_OFFS);
 	__ssp_writel(0, SIFIVE_SERIAL_IE_OFFS, ssp);
@@ -807,8 +805,7 @@ static void sifive_serial_console_write(
 	__ssp_writel(ier, SIFIVE_SERIAL_IE_OFFS, ssp);
 
 	if (locked)
-		uart_port_unlock(&ssp->port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&ssp->port, flags);
 }
 
 static int sifive_serial_console_setup(struct console *co, char *options)