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

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Date:	Fri, 15 Jul 2016 16:10:26 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Jacek Anaszewski <j.anaszewski@...sung.com>
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

* 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.

Sebastian