linux-kernel - Re: [PATCH] tty: serial: fixed uart irq maybe cause irq storm

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Date: Tue, 2 Apr 2024 14:45:12 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: "fengchunguo@....com" <fengchunguo@....com>
cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Jiri Slaby <jirislaby@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
    Gary Feng <chunguo.feng@...idrive.com>
Subject: Re: [PATCH] tty: serial: fixed uart irq maybe cause irq storm

On Mon, 1 Apr 2024, fengchunguo@....com wrote:

> From: "Gary Feng" <chunguo.feng@...idrive.com>
> 
> if not disable uart irq before disable clk,  uart irq maybe triggered after
> disabled clk immediately, then maybe cause irq storm.
> 
> Reproduced the below call trace, see i2c not be connected, but irq storm
> was triggered.

This doesn't really explain what's going on here. Why is the irq being 
triggered? You even seem to imply that nothing is connected so what 
triggers is triggering that irq? Can we selectively disable only that 
part, if it's e.g. empty tx condition or something?

> i2c_designware 30b70000.i2c: controller timed out
> CPU: 2 PID: 2932 Comm: gnss@...-servic 
> Tainted: G O 5.14.61-00094-geaa0149416cc-dirty #8
> Hardware name: Semidrive kunlun x9 REF Board (DT)
> Call trace:
> [<ffff00000808a3cc>] dump_backtrace+0x0/0x3c0
> [<ffff00000808a7a0>] show_stack+0x14/0x1c
> [<ffff000008cef43c>] dump_stack+0xc4/0xfc
> [<ffff00000814eb80>] __report_bad_irq+0x50/0xe0
> [<ffff00000814eaec>] note_interrupt+0x248/0x28c
> [<ffff00000814c0e8>] handle_irq_event+0x78/0xa4
> [<ffff00000814fcb8>] handle_fasteoi_irq+0xe4/0x1b4
> [<ffff00000814b060>] __handle_domain_irq+0x7c/0xbc
> [<ffff00000808176c>] gic_handle_irq+0x4c/0xb8
> [<ffff000008083230>] el1_irq+0xb0/0x124
> [<ffff000008d09f5c>] _raw_spin_unlock_irqrestore+0x10/0x44
> [<ffff00000865b784>] dw8250_set_termios+0x48/0xf4
> [<ffff0000086545a4>] serial8250_set_termios+0x14/0x28
> [<ffff00000864c4f4>] uart_change_speed+0x38/0x10c
> [<ffff00000864e458>] uart_set_termios+0xd0/0x17c
> [<ffff000008630ad4>] tty_set_termios+0x160/0x1e4
> [<ffff00000863165c>] set_termios+0x32c/0x3bc
> [<ffff000008631248>] tty_mode_ioctl+0x6f0/0x7d8
> [<ffff000008631a6c>] n_tty_ioctl_helper+0x10c/0x1e8
> [<ffff00000862d2c4>] n_tty_ioctl+0x120/0x194
> [<ffff00000862a724>] tty_ioctl+0x658/0xa34
> [<ffff0000082a8f40>] do_vfs_ioctl+0x554/0x810
> [<ffff0000082a9368>] SyS_ioctl+0x88/0x94
> Exception stack(0xffff00000ccf3ec0 to 0xffff00000ccf4000
> 
> Signed-off-by: chunguo.feng <chunguo.feng@...idrive.com>

Use your real name on signed-off line too. On From line you seem to 
provide different name as here.

-- 
 i.

> ---
>  drivers/tty/serial/8250/8250_dw.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index c1d43f0..133c24e 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -359,6 +359,12 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
>  
>  	rate = clk_round_rate(d->clk, newrate);
>  	if (rate > 0 && p->uartclk != rate) {
> +		/*Need disable uart irq before disabled clk, because uart irq maybe triggered after
> +		 * disabled clk immediately, then cause irq storm.
> +		 */
> +		if (p->irq)
> +			disabled_irq(p->irq);
> +
>  		clk_disable_unprepare(d->clk);
>  		/*
>  		 * Note that any clock-notifer worker will block in
> @@ -368,6 +374,9 @@ static void dw8250_set_termios(struct uart_port *p, struct ktermios *termios,
>  		if (!ret)
>  			p->uartclk = rate;
>  		clk_prepare_enable(d->clk);
> +
> +		if (p->irq)
> +			enable_irq(p->irq);
>  	}
>  
>  	dw8250_do_set_termios(p, termios, old);
>