From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Fri, 1 Mar 2024 22:45:15 +0100 Subject: [PATCH 02/18] serial: ar933x: 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/20240301215246.891055-3-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- 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/drivers/tty/serial/ar933x_uart.c:381 @ 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) @ linux-6.8.2-rt10/drivers/tty/serial/ar933x_uart.c:471 @ 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; } @ linux-6.8.2-rt10/drivers/tty/serial/ar933x_uart.c:630 @ 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 @ linux-6.8.2-rt10/drivers/tty/serial/ar933x_uart.c:653 @ 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)