On Fri, Oct 13, 2023 at 04:29:24PM +0000, Pavel Krasavin wrote:
> From: Pavel Krasavin <pkrasavin@xxxxxxxxxxx>
>
> 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.
>
> Fixes: ff7693d079e5 ("ARM: meson: serial: add MesonX SoC on-chip uart driver")
> Signed-off-by: Pavel Krasavin <pkrasavin@xxxxxxxxxxx>
> Reviewed-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
> Reviewed-by: Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxxxxx>
> ---
> v5: added missed Reviewed-by tags, Fixes tag added according to Dmitry and Neil notes
> v4: https://lore.kernel.org/lkml/OF55521400.7512350F-ON00258A47.003F7254-00258A47.0040E15C@xxxxxx/
> More correct patch subject according to Jiri's note
> v3: https://lore.kernel.org/lkml/OF6CF5FFA0.CCFD0E8E-ON00258A46.00549EDF-00258A46.0054BB62@xxxxxx/
> "From:" line added to the mail
> v2: https://lore.kernel.org/lkml/OF950BEF72.7F425944-ON00258A46.00488A76-00258A46.00497D44@xxxxxx/
> 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;
Hi,
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