From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Message-ID: Date: Mon, 17 Jul 2023 11:22:02 +0200 MIME-Version: 1.0 Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL Content-Language: en-US References: <20230717090735.19370-1-walter.chang@mediatek.com> From: AngeloGioacchino Del Regno In-Reply-To: <20230717090735.19370-1-walter.chang@mediatek.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+lwn-linux-arm-kernel=archive.lwn.net@lists.infradead.org List-Archive: To: walter.chang@mediatek.com, Mark Rutland , Marc Zyngier , Daniel Lezcano , Thomas Gleixner , Matthias Brugger Cc: 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 Il 17/07/23 11:07, walter.chang@mediatek.com ha scritto: > From: Walter Chang > > 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 Reviewed-by: AngeloGioacchino Del Regno > --- > 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; > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel