From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 1 Mar 2024 22:45:20 +0100
Subject: [PATCH 07/18] serial: pxa: Use uart_prepare_sysrq_char().

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/20240301215246.891055-8-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/pxa.c |   17 ++++++-----------
 1 file changed, 6 insertions(+), 11 deletions(-)

Index: linux-6.8.2-rt10/drivers/tty/serial/pxa.c
===================================================================
@ linux-6.8.2-rt10/drivers/tty/serial/pxa.c:154 @ static inline void receive_chars(struct
 				flag = TTY_FRAME;
 		}
 
-		if (uart_handle_sysrq_char(&up->port, ch))
+		if (uart_prepare_sysrq_char(&up->port, ch))
 			goto ignore_char;
 
 		uart_insert_char(&up->port, *status, UART_LSR_OE, ch, flag);
@ linux-6.8.2-rt10/drivers/tty/serial/pxa.c:235 @ static inline irqreturn_t serial_pxa_irq
 	check_modem_status(up);
 	if (lsr & UART_LSR_THRE)
 		transmit_chars(up);
-	uart_port_unlock(&up->port);
+	uart_unlock_and_check_sysrq(&up->port);
 	return IRQ_HANDLED;
 }
 
@ linux-6.8.2-rt10/drivers/tty/serial/pxa.c:607 @ serial_pxa_console_write(struct console
 	int locked = 1;
 
 	clk_enable(up->clk);
-	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
@ linux-6.8.2-rt10/drivers/tty/serial/pxa.c:628 @ serial_pxa_console_write(struct console
 	serial_out(up, UART_IER, ier);
 
 	if (locked)
-		uart_port_unlock(&up->port);
-	local_irq_restore(flags);
+		uart_port_unlock_irqrestore(&up->port, flags);
 	clk_disable(up->clk);
-
 }
 
 #ifdef CONFIG_CONSOLE_POLL