linux-kernel - Re: [PATCH v2] clocksource/drivers/sh_cmt: Always leave device running after probe

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Message-ID: <c07ae384-4042-43f4-b876-7207b72260f7@linaro.org>
Date: Wed, 5 Nov 2025 16:36:15 +0100
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Niklas Söderlund
 <niklas.soderlund+renesas@...natech.se>, Thomas Gleixner
 <tglx@...utronix.de>, Geert Uytterhoeven <geert@...ux-m68k.org>,
 linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Cc: Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v2] clocksource/drivers/sh_cmt: Always leave device
 running after probe

On 10/16/25 20:20, Niklas Söderlund wrote:
> The CMT device can be used as both a clocksource and a clockevent
> provider. The driver tries to be smart and power itself on and off, as
> well as enabling and disabling its clock when it's not in operation.
> This behavior is slightly altered if the CMT is used as an early
> platform device in which case the device is left powered on after probe,
> but the clock is still enabled and disabled at runtime.
> 
> This has worked for a long time, but recent improvements in PREEMPT_RT
> and PROVE_LOCKING have highlighted an issue. As the CMT registers itself
> as a clockevent provider, clockevents_register_device(), it needs to use
> raw spinlocks internally as this is the context of which the clockevent
> framework interacts with the CMT driver. However in the context of
> holding a raw spinlock the CMT driver can't really manage its power
> state or clock with calls to pm_runtime_*() and clk_*() as these calls
> end up in other platform drivers using regular spinlocks to control
> power and clocks.

So the fix is to remove PM management in the driver ?


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