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

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Date:	Thu, 14 Jul 2016 13:55:26 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Thomas Gleixner <tglx@...utronix.de>
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 07/14/2016 01:33 PM, Thomas Gleixner wrote:
> 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.

It was before my time in kernel, so I can only suppose that it was
the easiest way. Does it introduce some problems?

-- 
Best regards,
Jacek Anaszewski