Subject: [PATCH 02/18] serial: ar933x: Use uart_prepare_sysrq_char().
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 1 Mar 2024 22:45:15 +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/ar933x_uart.c |   18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/ar933x_uart.c
===================================================================
--- linux-6.8.2-rt10.orig/drivers/tty/serial/ar933x_uart.c
+++ linux-6.8.2-rt10/drivers/tty/serial/ar933x_uart.c
@@ -378,7 +378,7 @@ static void ar933x_uart_rx_chars(struct
 		up->port.icount.rx++;
 		ch = rdata & AR933X_UART_DATA_TX_RX_MASK;
 
-		if (uart_handle_sysrq_char(&up->port, ch))
+		if (uart_prepare_sysrq_char(&up->port, ch))
 			continue;
 
 		if ((up->port.ignore_status_mask & AR933X_DUMMY_STATUS_RD) == 0)
@@ -468,7 +468,7 @@ static irqreturn_t ar933x_uart_interrupt
 		ar933x_uart_tx_chars(up);
 	}
 
-	uart_port_unlock(&up->port);
+	uart_unlock_and_check_sysrq(&up->port);
 
 	return IRQ_HANDLED;
 }
@@ -627,14 +627,10 @@ static void ar933x_uart_console_write(st
 	unsigned int int_en;
 	int locked = 1;
 
-	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);
 
 	/*
 	 * First save the IER then disable the interrupts
@@ -654,9 +650,7 @@ static void ar933x_uart_console_write(st
 	ar933x_uart_write(up, AR933X_UART_INT_REG, AR933X_UART_INT_ALLINTS);
 
 	if (locked)
-		uart_port_unlock(&up->port);
-
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&up->port, flags);
 }
 
 static int ar933x_uart_console_setup(struct console *co, char *options)