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

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Date:   Fri, 18 Aug 2023 12:06:49 +0200
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     Walter Chang (張維哲) 
        <Walter.Chang@...iatek.com>, "maz@...nel.org" <maz@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        wsd_upstream <wsd_upstream@...iatek.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Chun-Hung Wu (巫駿宏) 
        <Chun-hung.Wu@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Stanley Chu (朱原陞) 
        <stanley.chu@...iatek.com>,
        Freddy Hsin (辛恒豐) 
        <Freddy.Hsin@...iatek.com>
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before
 programming CVAL

On 18/08/2023 11:29, Walter Chang (張維哲) wrote:
> On Mon, 2023-07-17 at 17:07 +0800, walter.chang@...iatek.com wrote:
>> From: Walter Chang <walter.chang@...iatek.com>
>> 
>> 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@...r.kernel.org
>> Signed-off-by: Walter Chang <walter.chang@...iatek.com>
>> ---
>>  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

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