linux-kernel - Re: [patch V2 43/67] leds/trigger/cpu: Convert to hotplug state machine

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Date:	Thu, 14 Jul 2016 13:33:06 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Anna-Maria Gleixner <anna-maria@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, rt@...utronix.de,
	Richard Cochran <rcochran@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org
Subject: Re: [patch V2 43/67] leds/trigger/cpu: Convert to hotplug state
 machine

On Thu, 14 Jul 2016, Jacek Anaszewski wrote:
> On 07/14/2016 11:41 AM, Peter Zijlstra wrote:
> > On Thu, Jul 14, 2016 at 10:10:55AM +0200, Jacek Anaszewski wrote:
> > > On 07/14/2016 09:47 AM, Ingo Molnar wrote:
> > > > 
> > > > * Jacek Anaszewski <j.anaszewski@...sung.com> wrote:
> > > > 
> > > > > > @@ -133,7 +125,13 @@ static int __init ledtrig_cpu_init(void)
> > > > > >        }
> > > > > > 
> > > > > >        register_syscore_ops(&ledtrig_cpu_syscore_ops);
> > > > > > -     register_cpu_notifier(&ledtrig_cpu_nb);
> > > > > > +
> > > > > > +     /*
> > > > > > +      * FIXME: Why needs this to happen in the interrupt disabled
> > > > > > +      * low level bringup phase of a cpu?
> > > > > > +      */
> > 
> > > Thanks for the explanation. I'm OK with that approach.
> > 
> > Since we have your attention, could you perhaps attempt to answer the
> > question so we can fix the fixme?
> > 
> 
> This is the way how all led triggers are being registered.
> 
> Once a trigger module is loaded it needs to be registered in
> the LED Trigger core.

That does not explain WHY this needs to happen in the low level bringup phase
of the CPU with interrupts disabled and can't be done from the normal ONLINE
callbacks in thread context.

Thanks,

	tglx