From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Fri, 1 Mar 2024 22:45:25 +0100 Subject: [PATCH 12/18] serial: sifive: Use uart_prepare_sysrq_char() to handle sysrq. 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 <palmer@dabbelt.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: linux-riscv@lists.infradead.org Link: https://lore.kernel.org/r/20240301215246.891055-13-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- 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/drivers/tty/serial/sifive.c:415 @ 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); @ linux-6.8.2-rt10/drivers/tty/serial/sifive.c:538 @ 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; } @ linux-6.8.2-rt10/drivers/tty/serial/sifive.c:795 @ 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); @ linux-6.8.2-rt10/drivers/tty/serial/sifive.c:808 @ 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)