There might be hard lockup if we set crtscts mode on port without RTS/CTS configured: # stty -F /dev/ttyAML6 crtscts; echo 1 > /dev/ttyAML6; echo 2 > /dev/ttyAML6 [ 95.890386] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [ 95.890857] rcu: 3-...0: (201 ticks this GP) idle=e33c/1/0x4000000000000000 softirq=5844/5846 fqs=4984 [ 95.900212] rcu: (detected by 2, t=21016 jiffies, g=7753, q=296 ncpus=4) [ 95.906972] Task dump for CPU 3: [ 95.910178] task:bash state:R running task stack:0 pid:205 ppid:1 flags:0x00000202 [ 95.920059] Call trace: [ 95.922485] __switch_to+0xe4/0x168 [ 95.925951] 0xffffff8003477508 [ 95.974379] watchdog: Watchdog detected hard LOCKUP on cpu 3 [ 95.974424] Modules linked in: 88x2cs(O) rtc_meson_vrtc Possible solution would be to not allow to setup crtscts on such port. Tested on S905X3 based board. Signed-off-by: Pavel Krasavin <pkrasavin@xxxxxxxxxxx> --- v2: braces for single statement removed according to Dmitry's note v1: https://lore.kernel.org/lkml/OF28B2B8C9.5BC0CD28-ON00258A46.0037688F-00258A46.0039155B@xxxxxx/ --- --- a/drivers/tty/serial/meson_uart.c 2023-10-12 15:44:02.410538523 +0300 +++ b/drivers/tty/serial/meson_uart.c 2023-10-12 15:58:06.242395253 +0300 @@ -380,10 +380,14 @@ static void meson_uart_set_termios(struc else val |= AML_UART_STOP_BIT_1SB; - if (cflags & CRTSCTS) - val &= ~AML_UART_TWO_WIRE_EN; - else + if (cflags & CRTSCTS) { + if (port->flags & UPF_HARD_FLOW) + val &= ~AML_UART_TWO_WIRE_EN; + else + termios->c_cflag &= ~CRTSCTS; + } else { val |= AML_UART_TWO_WIRE_EN; + } writel(val, port->membase + AML_UART_CONTROL); @@ -705,6 +709,7 @@ static int meson_uart_probe(struct platf u32 fifosize = 64; /* Default is 64, 128 for EE UART_0 */ int ret = 0; int irq; + bool has_rtscts; if (pdev->dev.of_node) pdev->id = of_alias_get_id(pdev->dev.of_node, "serial"); @@ -732,6 +737,7 @@ static int meson_uart_probe(struct platf return irq; of_property_read_u32(pdev->dev.of_node, "fifo-size", &fifosize); + has_rtscts = of_property_read_bool(pdev->dev.of_node, "uart-has-rtscts"); if (meson_ports[pdev->id]) { return dev_err_probe(&pdev->dev, -EBUSY, @@ -762,6 +768,8 @@ static int meson_uart_probe(struct platf port->mapsize = resource_size(res_mem); port->irq = irq; port->flags = UPF_BOOT_AUTOCONF | UPF_LOW_LATENCY; + if (has_rtscts) + port->flags |= UPF_HARD_FLOW; port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_MESON_CONSOLE); port->dev = &pdev->dev; port->line = pdev->id;
