linux-kernel - Re: [PATCH 3/6] ARM: EXYNOS: add Exynos Dual Cluster Support

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Date:	Fri, 4 Oct 2013 15:51:31 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Dave Martin <Dave.Martin@....com>
cc:	Vyacheslav Tyrtov <v.tyrtov@...sung.com>,
	Mark Rutland <mark.rutland@....com>,
	devicetree@...r.kernel.org, Kukjin Kim <kgene.kim@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Stephen Warren <swarren@...dotorg.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	linux-samsung-soc@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Ben Dooks <ben-linux@...ff.org>,
	Tarek Dakhran <t.dakhran@...sung.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Naour Romain <romain.naour@...nwide.fr>,
	Mike Turquette <mturquette@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Heiko Stuebner <heiko@...ech.de>
Subject: Re: [PATCH 3/6] ARM: EXYNOS: add Exynos Dual Cluster Support

On Wed, 2 Oct 2013, Dave Martin wrote:

> On Tue, Oct 01, 2013 at 08:17:04PM +0400, Vyacheslav Tyrtov wrote:
> > +static int exynos_power_up(unsigned int cpu, unsigned int cluster)
> > +{
> > +     int ret;
> > +     local_irq_disable();
> 
> Should there be a local_fiq_disable() here also?

No.  In fact this is paired with

> > +     arch_spin_lock(&exynos_lock);

to create the equivalent of a arch_spin_lock_irq().  And the reason is:

/*
 * We can't use regular spinlocks. In the switcher case, it is possible
 * for an outbound CPU to call power_down() after its inbound counterpart
 * is already live using the same logical CPU number which trips lockdep
 * debugging.
 */

Otherwise we simply would have used spin_lock_irq().

No FIQs are supposed to ever race with this code.


Nicolas
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