From: Caleb James DeLisle <cjd@cjdns.fr>
To: kpursoty@proton.me,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
"tglx@linutronix.de" <tglx@linutronix.de>
Cc: "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
"tsbogend@alpha.franken.de" <tsbogend@alpha.franken.de>,
"naseefkm@gmail.com" <naseefkm@gmail.com>
Subject: Re: [PATCH v2 2/2] clocksource: timer-econet-en751221: fix IRQ ack storm on interrupt handler
Date: Tue, 14 Apr 2026 15:20:51 +0200 [thread overview]
Message-ID: <04bce292-00c0-4669-964d-c94bd7179bb5@cjdns.fr> (raw)
In-Reply-To: <cAKrsEu2h3qUcucFHNb4TH61fInUPSG1Z6gefgAecIzRCGrhzAflYboWuY7ANYSLaGoEbH6_ypWsmMGv9IituYBbiWoR9y6Ux29IBA7ozCM=@proton.me>
On 13/04/2026 18:04, kpursoty@proton.me wrote:
> The interrupt handler acked by writing the current count back to compare:
>
> iowrite32(ioread32(reg_count(cpu)), reg_compare(cpu));
>
> Since the interrupt fires when count >= compare, and the counter advances
> past the written value before the MMIO write reaches the peripheral, the
> condition re-asserts on the same bus cycle. This causes a tight IRQ storm
> on CPU0, stalling boot at T=62s (measured: boot never progresses past
> clockevents registration).
>
> The EcoNet GPL kernel (arch/mips/econet/time2.c, cputmr_timer_ack()) acks
> by writing the *next* deadline, which puts count < compare and clears the
> pending condition. Write U32_MAX (unreachable before set_next_event()
> programs the real deadline), consistent with cevt_dev_init() which also
> writes U32_MAX to park the compare register at init.
>
> Fixes: 3b4c33ac87d0 ("clocksource/drivers: Add EcoNet Timer HPT driver")
> Signed-off-by: Kervin Pursoty <kpursoty@proton.me>
I don't understand the subsystem well enough to know if this is correct,
but it boots on EN751221.
Tested-by: Caleb James DeLisle <cjd@cjdns.fr>
> ---
> drivers/clocksource/timer-econet-en751221.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/clocksource/timer-econet-en751221.c b/drivers/clocksource/timer-econet-en751221.c
> --- a/drivers/clocksource/timer-econet-en751221.c
> +++ b/drivers/clocksource/timer-econet-en751221.c
> @@ -68,6 +68,10 @@ static irqreturn_t cevt_interrupt(int irq, void *dev_id)
> if (!cevt_is_pending(cpu))
> return IRQ_NONE;
>
> - iowrite32(ioread32(reg_count(cpu)), reg_compare(cpu));
> + /*
> + * Ack: write a future value so count < compare, clearing the pending
> + * condition. set_next_event() will program the real deadline.
> + */
> + iowrite32(U32_MAX, reg_compare(cpu));
> dev->event_handler(dev);
> return IRQ_HANDLED;
> }
>
prev parent reply other threads:[~2026-04-14 13:21 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-13 16:04 [PATCH v2 2/2] clocksource: timer-econet-en751221: fix IRQ ack storm on interrupt handler kpursoty
2026-04-14 13:20 ` Caleb James DeLisle [this message]
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