Re: [PATCH v5] tty: serial: meson: fix hard LOCKUP on crtscts mode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Fri, Oct 13, 2023 at 04:29:24PM +0000, Pavel Krasavin wrote:
> From: Pavel Krasavin <pkrasavin@imaqliq.com>
> 
> 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@imaqliq.com>
> Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
> Reviewed-by: Dmitry Rokosov <ddrokosov@salutedevices.com>
> ---
> 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@gdc.ru/
> More correct patch subject according to Jiri's note
> v3: https://lore.kernel.org/lkml/OF6CF5FFA0.CCFD0E8E-ON00258A46.00549EDF-00258A46.0054BB62@gdc.ru/
> "From:" line added to the mail
> v2: https://lore.kernel.org/lkml/OF950BEF72.7F425944-ON00258A46.00488A76-00258A46.00497D44@gdc.ru/
> braces for single statement removed according to Dmitry's note
> v1: https://lore.kernel.org/lkml/OF28B2B8C9.5BC0CD28-ON00258A46.0037688F-00258A46.0039155B@gdc.ru/
> ---
> 
> --- 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,

This is the friendly patch-bot of Greg Kroah-Hartman.  You have sent him
a patch that has triggered this response.  He used to manually respond
to these common problems, but in order to save his sanity (he kept
writing the same thing over and over, yet to different people), I was
created.  Hopefully you will not take offence and will fix the problem
in your patch and resubmit it so that it can be accepted into the Linux
kernel tree.

You are receiving this message because of the following common error(s)
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- You have marked a patch with a "Fixes:" tag for a commit that is in an
  older released kernel, yet you do not have a cc: stable line in the
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  follow the documented rules in the
  Documentation/process/stable-kernel-rules.rst file for how to resolve
  this.

If you wish to discuss this problem further, or you have questions about
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Greg will reply once he has dug out from the pending patches received
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thanks,

greg k-h's patch email bot

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