Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:2 as permitted sender) client-ip=2620:137:e000::3:2;
Date:   Mon, 18 Sep 2023 12:11:14 +0100
Message-ID: <864jjrenxp.wl-maz@kernel.org>
From:   Marc Zyngier <maz@kernel.org>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org, daniel.lezcano@linaro.org,
        linux-kernel@vger.kernel.org, tglx@linutronix.de
Subject: Re: [PATCH] clocksource/drivers/arm_arch_timer: Initialize evtstrm after finalizing cpucaps
In-Reply-To: <20230907133410.3817800-1-mark.rutland@arm.com>
References: <20230907133410.3817800-1-mark.rutland@arm.com>
User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue)
 FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2
 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO)
MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue")
Content-Type: text/plain; charset=US-ASCII
Precedence: bulk

On Thu, 07 Sep 2023 14:34:10 +0100,
Mark Rutland <mark.rutland@arm.com> 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@arm.com>
> Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>

Acked-by: Marc Zyngier <maz@kernel.org>

	M.

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