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From: Marc Zyngier <maz@kernel.org>
To: <walter.chang@mediatek.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	"Daniel Lezcano" <daniel.lezcano@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno 
	<angelogioacchino.delregno@collabora.com>,
	<wsd_upstream@mediatek.com>, <stanley.chu@mediatek.com>,
	<Chun-hung.Wu@mediatek.com>, <Freddy.Hsin@mediatek.com>,
	<stable@vger.kernel.org>, <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL
Date: Mon, 17 Jul 2023 10:19:08 +0100	[thread overview]
Message-ID: <867cqyvqsz.wl-maz@kernel.org> (raw)
In-Reply-To: <20230717090735.19370-1-walter.chang@mediatek.com>

On Mon, 17 Jul 2023 10:07:34 +0100,
<walter.chang@mediatek.com> wrote:
> 
> From: Walter Chang <walter.chang@mediatek.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@vger.kernel.org
> Signed-off-by: Walter Chang <walter.chang@mediatek.com>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: walter.chang@mediatek.com
Cc: Mark Rutland <mark.rutland@arm.com>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	AngeloGioacchino Del Regno
	<angelogioacchino.delregno@collabora.com>,
	wsd_upstream@mediatek.com, stanley.chu@mediatek.com,
	Chun-hung.Wu@mediatek.com, Freddy.Hsin@mediatek.com,
	stable@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL
Date: Mon, 17 Jul 2023 10:19:08 +0100	[thread overview]
Message-ID: <867cqyvqsz.wl-maz@kernel.org> (raw)
In-Reply-To: <20230717090735.19370-1-walter.chang@mediatek.com>

On Mon, 17 Jul 2023 10:07:34 +0100,
<walter.chang@mediatek.com> wrote:
> 
> From: Walter Chang <walter.chang@mediatek.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@vger.kernel.org
> Signed-off-by: Walter Chang <walter.chang@mediatek.com>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.

_______________________________________________
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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-07-17  9:19 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-17  9:07 [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL walter.chang
2023-07-17  9:19 ` Marc Zyngier [this message]
2023-07-17  9:19   ` Marc Zyngier
2023-07-17  9:22 ` AngeloGioacchino Del Regno
2023-07-17  9:22   ` AngeloGioacchino Del Regno
2023-08-18  9:29 ` Walter Chang (張維哲)
2023-08-18 10:06   ` Daniel Lezcano
2023-08-18 10:06     ` Daniel Lezcano
2023-08-31  1:31 ` [tip: timers/core] " tip-bot2 for Walter Chang

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