linux-kernel - Re: [PATCH v6 1/6] ARM: make register_current_timer

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Message-ID: <aSB_bUbfjenD1fjZ@shell.armlinux.org.uk>
Date: Fri, 21 Nov 2025 15:04:13 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Will McVicker <willmcvicker@...gle.com>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Krzysztof Kozlowski <krzk@...nel.org>,
	Alim Akhtar <alim.akhtar@...sung.com>,
	Donghoon Yu <hoony.yu@...sung.com>,
	Hosung Kim <hosung0.kim@...sung.com>, Rob Herring <robh@...nel.org>,
	John Stultz <jstultz@...gle.com>,
	Youngmin Nam <youngmin.nam@...sung.com>,
	Peter Griffin <peter.griffin@...aro.org>,
	Tudor Ambarus <tudor.ambarus@...aro.org>,
	André Draszik <andre.draszik@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	linux-samsung-soc@...r.kernel.org, kernel-team@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 1/6] ARM: make register_current_timer_delay()
 accessible after init

On Thu, Nov 20, 2025 at 06:42:29PM +0000, Will McVicker wrote:
> The function register_current_timer_delay() is called from the
> exynos_mct clocksource driver at probe time. In the event that the
> exynos_mct driver is probed deferred or the platform manually unbinds
> and rebinds the driver we need this function available. So drop the
> __init tag.

First question. Why.

Second, have you analysed the code to check that you _can_ call this
after init time?

Let's look at the code:

        if (!delay_calibrated && (!delay_res || (res < delay_res))) {
        } else {
                pr_info("Ignoring duplicate/late registration of read_current_ti
mer delay\n");
        }

So, if delay_calibrated is set, then this will fail. When is that set?
It's set by calibrate_delay_is_known() and calibration_delay_done().
When are these called? Basically after calibrate_delay() has finished.
When is calibrate_delay() called? It's called by start_kernel(), while
the init sections are still present.

So, calling this _after_ the init sections has been freed will result
in the above pr_info() printed and this function doing *nothing*.
So it's utterly pointless to call if the init sections have been freed.

Please find a different solution.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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