Subject: [PATCH 10/18] serial: owl: Use uart_prepare_sysrq_char() to handle sysrq.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 1 Mar 2024 22:45:23 +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: Andreas Färber <[email-masked]>
Cc: Manivannan Sadhasivam <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 drivers/tty/serial/owl-uart.c |   30 ++++++++++++------------------
 1 file changed, 12 insertions(+), 18 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/owl-uart.c
===================================================================
--- linux-6.8.2-rt10.orig/drivers/tty/serial/owl-uart.c
+++ linux-6.8.2-rt10/drivers/tty/serial/owl-uart.c
@@ -199,6 +199,7 @@ static void owl_uart_receive_chars(struc
 	stat = owl_uart_read(port, OWL_UART_STAT);
 	while (!(stat & OWL_UART_STAT_RFEM)) {
 		char flag = TTY_NORMAL;
+		bool sysrq;
 
 		if (stat & OWL_UART_STAT_RXER)
 			port->icount.overrun++;
@@ -217,7 +218,9 @@ static void owl_uart_receive_chars(struc
 		val = owl_uart_read(port, OWL_UART_RXDAT);
 		val &= 0xff;
 
-		if ((stat & port->ignore_status_mask) == 0)
+		sysrq = uart_prepare_sysrq_char(port, val);
+
+		if (!sysrq && (stat & port->ignore_status_mask) == 0)
 			tty_insert_flip_char(&port->state->port, val, flag);
 
 		stat = owl_uart_read(port, OWL_UART_STAT);
@@ -229,10 +232,9 @@ static void owl_uart_receive_chars(struc
 static irqreturn_t owl_uart_irq(int irq, void *dev_id)
 {
 	struct uart_port *port = dev_id;
-	unsigned long flags;
 	u32 stat;
 
-	uart_port_lock_irqsave(port, &flags);
+	uart_port_lock(port);
 
 	stat = owl_uart_read(port, OWL_UART_STAT);
 
@@ -246,7 +248,7 @@ static irqreturn_t owl_uart_irq(int irq,
 	stat |= OWL_UART_STAT_RIP | OWL_UART_STAT_TIP;
 	owl_uart_write(port, stat, OWL_UART_STAT);
 
-	uart_port_unlock_irqrestore(port, flags);
+	uart_unlock_and_check_sysrq(port);
 
 	return IRQ_HANDLED;
 }
@@ -508,18 +510,12 @@ static void owl_uart_port_write(struct u
 {
 	u32 old_ctl, val;
 	unsigned long flags;
-	int locked;
+	int locked = 1;
 
-	local_irq_save(flags);
-
-	if (port->sysrq)
-		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);
 
 	old_ctl = owl_uart_read(port, OWL_UART_CTL);
 	val = old_ctl | OWL_UART_CTL_TRFS_TX;
@@ -541,9 +537,7 @@ static void owl_uart_port_write(struct u
 	owl_uart_write(port, old_ctl, OWL_UART_CTL);
 
 	if (locked)
-		uart_port_unlock(port);
-
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(port, flags);
 }
 
 static void owl_uart_console_write(struct console *co, const char *s,