linux-kernel - Re: [PATCH 1/2] clocksource: imx-tpm: fix return -ETIME when delta exceeds INT

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Message-ID: <ZsOSNC/5BvTQAiAe@lizhi-Precision-Tower-5810>
Date: Mon, 19 Aug 2024 14:43:00 -0400
From: Frank Li <Frank.li@....com>
To: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>,
	Dong Aisheng <aisheng.dong@....com>,
	"open list:CLOCKSOURCE, CLOCKEVENT DRIVERS" <linux-kernel@...r.kernel.org>,
	"open list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <imx@...ts.linux.dev>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] clocksource: imx-tpm: fix return -ETIME when delta
 exceeds INT_MAX

On Mon, Aug 19, 2024 at 03:21:36PM +0200, Daniel Lezcano wrote:
> On 25/07/2024 21:33, Frank Li wrote:
> > From: Jacky Bai <ping.bai@....com>
> >
> > In tpm_set_next_event(delta), return -ETIME by wrong cast to int when delta
> > is larger than INT_MAX.
>
> Is it something you observed or from your understanding of the code ?

System use this timer to wakeup from lower idle, which core and local timer
turn off. -ETIME may prevent system enter lower idle, or failure wakeup
from lower idle utill counter run overflow. I am not sure how to trigger
this problem.

Assume run at 24Mhz, 1/24us * 0x8000_0000 is around 89s. Problem trigger
only next event bigger 89s, which relative quite big number.

Anyways, the original code is wrong, it claim max delta is 32bit.

Jack bai: any additonal supplement for this?

Frank

>
> > For example:
> >
> > tpm_set_next_event(delta = 0xffff_fffe)
> > {
> >          ...
> >          next = tpm_read_counter(); // assume next is 0x10
> >          next += delta; // next will 0xffff_fffe + 0x10 = 0x1_0000_000e
> >          now = tpm_read_counter();  // now is 0x10
> >          ...
> >
> >          return (int)(next - now) <= 0 ? -ETIME : 0;
> >                       ^^^^^^^^^^
> >                       0x1_0000_000e - 0x10 = 0xffff_fffe, which is -2 when
> >                       cast to int. So return -ETIME.
> > }
> >
> > To fix this, introduce a 'prev' variable and check if 'now - prev' is
> > larger than delta.
> >
> > Cc: <stable@...r.kernel.org>
> > Fixes: 059ab7b82eec ("clocksource/drivers/imx-tpm: Add imx tpm timer support")
> > Signed-off-by: Jacky Bai <ping.bai@....com>
> > Reviewed-by: Peng Fan <peng.fan@....com>
> > Reviewed-by: Ye Li <ye.li@....com>
> > Reviewed-by: Jason Liu <jason.hui.liu@....com>
> > Signed-off-by: Frank Li <Frank.Li@....com>
> > ---
> >   drivers/clocksource/timer-imx-tpm.c | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/clocksource/timer-imx-tpm.c b/drivers/clocksource/timer-imx-tpm.c
> > index bd64a8a8427f3..cd23caf1e5999 100644
> > --- a/drivers/clocksource/timer-imx-tpm.c
> > +++ b/drivers/clocksource/timer-imx-tpm.c
> > @@ -83,10 +83,10 @@ static u64 notrace tpm_read_sched_clock(void)
> >   static int tpm_set_next_event(unsigned long delta,
> >   				struct clock_event_device *evt)
> >   {
> > -	unsigned long next, now;
> > +	unsigned long next, prev, now;
> > -	next = tpm_read_counter();
> > -	next += delta;
> > +	prev = tpm_read_counter();
> > +	next = prev + delta;
> >   	writel(next, timer_base + TPM_C0V);
> >   	now = tpm_read_counter();
> > @@ -96,7 +96,7 @@ static int tpm_set_next_event(unsigned long delta,
> >   	 * of writing CNT registers which may cause the min_delta event got
> >   	 * missed, so we need add a ETIME check here in case it happened.
> >   	 */
> > -	return (int)(next - now) <= 0 ? -ETIME : 0;
> > +	return (now - prev) >= delta ? -ETIME : 0;
> >   }
> >   static int tpm_set_state_oneshot(struct clock_event_device *evt)
>
>
> --
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