[PATCH] tty: serial: fixed uart irq maybe cause irq storm

[PATCH] tty: serial: fixed uart irq maybe cause irq storm

[fengchunguo]

From: "chunguo.feng" <chunguo.feng@semidrive.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.

i2c_designware 30b70000.i2c: controller timed out
CPU: 2 PID: 2932 Comm: gnss@1.0-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@semidrive.com>
---
 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);
-- 
2.7.4

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

[Greg KH]

On Mon, Apr 01, 2024 at 05:30:01PM +0800, fengchunguo@126.com wrote:
> From: "chunguo.feng" <chunguo.feng@semidrive.com>

Please use your name, which is not with a "." in it, right?

> 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.
> 
> i2c_designware 30b70000.i2c: controller timed out
> CPU: 2 PID: 2932 Comm: gnss@1.0-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@semidrive.com>
> ---
>  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

Space needed after '*', right?

> +		 * disabled clk immediately, then cause irq storm.
> +		 */
> +		if (p->irq)
> +			disabled_irq(p->irq);

This feels wrong, the irq should not be turned off here, what happens if
some data comes in while this function is running?  Will it be lost?

thanks,

greg k-h

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

[Ilpo Järvinen]

[-- Attachment #1: Type: text/plain, Size: 726 bytes --]

On Mon, 1 Apr 2024, Feng Chunguo wrote:

> Hi Greg KH，
> 
> Sent this path again.
> 
>  the irq should not be turned off here, what happens if some data comes in while this
> function is running?  Will it be lost?
> --> lost，not receive other irq.
> 
>  When the uart was switching the baud rate from one to other,  this issue can be
> reproduced.


>> This feels wrong,
>> the irq should not be turned off here, what happens if some data comes in while this
>> function is running? Will it be lost? thanks, greg k-h

Changing rate always risks losing what's currently on wire due to timing 
related corruption, I don't think there there's a way around that IRQ 
being enabled or not.


-- 
 i.

[PATCH] tty: serial: fixed uart irq maybe cause irq storm

[fengchunguo]

From: "Gary Feng" <chunguo.feng@semidrive.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.

i2c_designware 30b70000.i2c: controller timed out
CPU: 2 PID: 2932 Comm: gnss@1.0-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@semidrive.com>
---
 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);
-- 
2.7.4

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

[Greg KH]

On Mon, Apr 01, 2024 at 06:19:06PM +0800, fengchunguo@126.com wrote:
> From: "Gary Feng" <chunguo.feng@semidrive.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.
> 
> i2c_designware 30b70000.i2c: controller timed out
> CPU: 2 PID: 2932 Comm: gnss@1.0-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@semidrive.com>
> ---
>  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);
> -- 
> 2.7.4
> 

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)
as indicated below:

- This looks like a new version of a previously submitted patch, but you
  did not list below the --- line any changes from the previous version.
  Please read the section entitled "The canonical patch format" in the
  kernel file, Documentation/process/submitting-patches.rst for what
  needs to be done here to properly describe this.

If you wish to discuss this problem further, or you have questions about
how to resolve this issue, please feel free to respond to this email and
Greg will reply once he has dug out from the pending patches received
from other developers.

thanks,

greg k-h's patch email bot

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

[Ilpo Järvinen]

On Mon, 1 Apr 2024, fengchunguo@126.com wrote:

> From: "Gary Feng" <chunguo.feng@semidrive.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@1.0-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@semidrive.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);
> 

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

[Andy Shevchenko]

On Mon, Apr 01, 2024 at 06:19:06PM +0800, fengchunguo@126.com wrote:
> From: "Gary Feng" <chunguo.feng@semidrive.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.

> i2c_designware 30b70000.i2c: controller timed out
> CPU: 2 PID: 2932 Comm: gnss@1.0-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

Please read
https://www.kernel.org/doc/html/latest/process/submitting-patches.html#backtraces-in-commit-messages
and update the commit message accordingly.

...

> +		/*Need disable uart irq before disabled clk, because uart irq maybe triggered after
> +		 * disabled clk immediately, then cause irq storm.
> +		 */


/*
 * Use canonical multi-line comment
 * style and make sure the lines are not
 * too long.
 */

...

FWIW, the patch that compares this with current clock rate most likely will be
reverted, meaning your fix might be not needed anymore, or has to be rebased.

-- 
With Best Regards,
Andy Shevchenko