Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL

[Daniel Lezcano]

On 18/08/2023 11:29, Walter Chang (張維哲) wrote:
> On Mon, 2023-07-17 at 17:07 +0800, walter.chang@xxxxxxxxxxxx wrote:
> > From: Walter Chang <walter.chang@xxxxxxxxxxxx>
> >
> > Due to the fact that the use of `writeq_relaxed()` to program CVAL is
> > not guaranteed to be atomic, it is necessary to disable the timer
> > before
> > programming CVAL.
> >
> > However, if the MMIO timer is already enabled and has not yet
> > expired,
> > there is a possibility of unexpected behavior occurring: when the CPU
> > enters the idle state during this period, and if the CPU's local
> > event
> > is earlier than the broadcast event, the following process occurs:
> >
> > tick_broadcast_enter()
> >   tick_broadcast_oneshot_control(TICK_BROADCAST_ENTER)
> >     __tick_broadcast_oneshot_control()
> >       ___tick_broadcast_oneshot_control()
> >         tick_broadcast_set_event()
> >           clockevents_program_event()
> >             set_next_event_mem()
> >
> > During this process, the MMIO timer remains enabled while programming
> > CVAL. To prevent such behavior, disable timer explicitly prior to
> > programming CVAL.
> >
> > Fixes: 8b82c4f883a7 ("clocksource/drivers/arm_arch_timer: Move MMIO
> > timer programming over to CVAL")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Walter Chang <walter.chang@xxxxxxxxxxxx>
> > ---
> >  drivers/clocksource/arm_arch_timer.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/clocksource/arm_arch_timer.c
> > b/drivers/clocksource/arm_arch_timer.c
> > index e733a2a1927a..7dd2c615bce2 100644
> > --- a/drivers/clocksource/arm_arch_timer.c
> > +++ b/drivers/clocksource/arm_arch_timer.c
> > @@ -792,6 +792,13 @@ static __always_inline void
> > set_next_event_mem(const int access, unsigned long e
> >  u64 cnt;
> >  
> >  ctrl = arch_timer_reg_read(access, ARCH_TIMER_REG_CTRL, clk);
> > +
> > +/* Timer must be disabled before programming CVAL */
> > +if (ctrl & ARCH_TIMER_CTRL_ENABLE) {
> > +ctrl &= ~ARCH_TIMER_CTRL_ENABLE;
> > +arch_timer_reg_write(access, ARCH_TIMER_REG_CTRL, ctrl,
> > clk);
> > +}
> > +
> >  ctrl |= ARCH_TIMER_CTRL_ENABLE;
> >  ctrl &= ~ARCH_TIMER_CTRL_IT_MASK;
> >  
>
> Gentle ping for this patch.

Applied, thanks

--
<http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog