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

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Message-id: <578C92BC.2070603@samsung.com>
Date:	Mon, 18 Jul 2016 10:26:36 +0200
From:	Jacek Anaszewski <j.anaszewski@...sung.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	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>,
	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,
	Pawel Moll <pawel.moll@....com>
Subject: Re: [patch V2 43/67] leds/trigger/cpu: Convert to hotplug state machine

Hi Sebastian,

On 07/15/2016 04:10 PM, Sebastian Andrzej Siewior wrote:
> * Jacek Anaszewski | 2016-07-14 13:55:26 [+0200]:
>
>> On 07/14/2016 01:33 PM, Thomas Gleixner wrote:
>>> 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?
>
> It was introduced by Pawel Moll in fba14ae8e924 ("ledtrig-cpu: Handle
> CPU hot(un)plugging"). It does not introduce any problems but those
> bring up / bring down levels are usually used by the core code. This
> does not look like it needs to be done _that_ early or late during the
> removal / addition of a CPU to the system.
>
> Which means this looks like it could be moved to CPU_ONLINE /
> CPU_DOWN_PREPARE which in turns means we could use dynamic IDs instead
> of those hardcoded ones since the LED subsystem does not depend on other
> components.

 From the LED subsystem perspective I don't see any particular reason
for which it couldn't be accomplished from the ONLINE callbacks.

-- 
Best regards,
Jacek Anaszewski