linux-kernel - [tip: timers/core] clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL

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Message-ID: <169344549125.27769.12141832888285612351.tip-bot2@tip-bot2>
Date:   Thu, 31 Aug 2023 01:31:31 -0000
From:   "tip-bot2 for Walter Chang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     stable@...r.kernel.org, Walter Chang <walter.chang@...iatek.com>,
        Marc Zyngier <maz@...nel.org>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: timers/core] clocksource/drivers/arm_arch_timer: Disable timer
 before programming CVAL

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     e7d65e40ab5a5940785c5922f317602d0268caaf
Gitweb:        https://git.kernel.org/tip/e7d65e40ab5a5940785c5922f317602d0268caaf
Author:        Walter Chang <walter.chang@...iatek.com>
AuthorDate:    Mon, 17 Jul 2023 17:07:34 +08:00
Committer:     Daniel Lezcano <daniel.lezcano@...aro.org>
CommitterDate: Fri, 18 Aug 2023 12:06:16 +02:00

clocksource/drivers/arm_arch_timer: Disable timer before programming CVAL

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>
Acked-by: Marc Zyngier <maz@...nel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
Link: https://lore.kernel.org/r/20230717090735.19370-1-walter.chang@mediatek.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 e09d442..f6c5f89 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -774,6 +774,13 @@ 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;