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

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Message-ID: <20251013073209.GA3585900@ragnatech.se>
Date: Mon, 13 Oct 2025 09:32:09 +0200
From: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org
Subject: Re: [RFC] clocksource/drivers/sh_cmt: Always leave device running
 after probe

Hi Wolfram,

On 2025-10-13 09:22:17 +0200, Wolfram Sang wrote:
> Hi Niklas,
> 
> thanks for your work on these timers!
> 
> > For non-PREEMPT_RT builds this is not really an issue, but for
> > PREEMPT_RT builds where normal spinlocks can sleep this might be an
> > issue. Be cautious and always leave the power and clock running after
> > probe.
> 
> I am not a super-duper PM expert but this sounds pretty reasonable to
> me. Only minor comments:
> 
> >  		ret = -ETIMEDOUT;
> > -		goto err1;
> > +		return ret;
> 
> return -ETIMEDOUT;

Wops, indeed. Thanks for spotting it. Will wait for feedback on the 
general idea and fix this in v2.

> 
> >  	if (!(ch->flags & (FLAG_CLOCKEVENT | FLAG_CLOCKSOURCE))) {
> > -		pm_runtime_get_sync(&ch->cmt->pdev->dev);
> >  		ret = sh_cmt_enable(ch);
> >  	}
> 
> Curly braces can go.
> 
> >  	if (f && !(ch->flags & (FLAG_CLOCKEVENT | FLAG_CLOCKSOURCE))) {
> >  		sh_cmt_disable(ch);
> > -		pm_runtime_put(&ch->cmt->pdev->dev);
> >  	}
> 
> ditto.
> 
> And I don't if this is a seperate patch or not, but we could simplify
> probe a little by using 'clk_prepare_enable()'...

This is a good idea, I would prefer to it in a separate patch. I'm 
always a bit scared touching this driver and making finding issues with 
bisect easier is always a good idea :-)

> 
> Happy hacking,
> 
>    Wolfram
> 



-- 
Kind Regards,
Niklas Söderlund