linux-kernel - Re: [PATCH] clocksource/drivers/arm_arch_timer: Initialize evtstrm after finalizing cpucaps

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Date:   Fri, 15 Sep 2023 21:14:25 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     daniel.lezcano@...aro.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, maz@...nel.org
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Initialize evtstrm
 after finalizing cpucaps

On Thu, Sep 07 2023 at 14:34, Mark Rutland wrote:

> We attempt to initialize each CPU's arch_timer event stream in
> arch_timer_evtstrm_enable(), which we call from the
> arch_timer_starting_cpu() cpu hotplug callback which is registered early
> in boot. As this is registered before we initialize the system cpucaps,
> the test for ARM64_HAS_ECV will always be false for CPUs present at boot
> time, and will only be taken into account for CPUs onlined late
> (including those which are hotplugged out and in again).
>
> Due to this, CPUs present and boot time may not use the intended divider
> and scale factor to generate the event stream, and may differ from other
> CPUs.
>
> Correct this by only initializing the event stream after cpucaps have been
> finalized, registering a separate CPU hotplug callback for the event stream
> configuration. Since the caps must be finalized by this point, use
> spus_have_final_cap() to verify this.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Marc Zyngier <maz@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>

Acked-by: Thomas Gleixner <tglx@...utronix.de>