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

From: Frank Li
Date: Mon Aug 19 2024 - 14:44:59 EST


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@xxxxxxx>
> >
> > 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@xxxxxxxxxxxxxxx>
> > Fixes: 059ab7b82eec ("clocksource/drivers/imx-tpm: Add imx tpm timer support")
> > Signed-off-by: Jacky Bai <ping.bai@xxxxxxx>
> > Reviewed-by: Peng Fan <peng.fan@xxxxxxx>
> > Reviewed-by: Ye Li <ye.li@xxxxxxx>
> > Reviewed-by: Jason Liu <jason.hui.liu@xxxxxxx>
> > Signed-off-by: Frank Li <Frank.Li@xxxxxxx>
> > ---
> > 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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