linux-kernel - Re: A question about Cortex-A73 erratum 858921

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Date:   Fri, 09 Sep 2022 13:23:38 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Kunkun Jiang <jiangkunkun@...wei.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        "Daniel Lezcano" <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "wanghaibin.wang@...wei.com" <wanghaibin.wang@...wei.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: A question about Cortex-A73 erratum 858921

On Fri, 09 Sep 2022 08:31:43 +0100,
Kunkun Jiang <jiangkunkun@...wei.com> wrote:
> 
> Hi all,
> 
> Recently I am learning the code related to Arm arch timer. I found that the
> Cortex-A73 erratum 858921 does not set the corresponding callback functions:
> set_next_event_phys and set_next_event_virt like other erratums. Won't it
> get the wrong value when reading the counter during setting next event?

Yup, you're correct.

This is a regression introduced by a38b71b0833e
("clocksource/drivers/arm_arch_timer: Move system register timer
programming over to CVAL"). We used to use the TVAL accessor which
doesn't need a read of the counter, while the switch to CVAL needs
one. Obviously, I didn't enough pay attention to the A73 erratum.

Please send in a fix for this.

Thanks,

	M.

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