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

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Date:	Wed, 2 Oct 2013 14:05:50 +0100
From:	Dave Martin <Dave.Martin@....com>
To:	Nicolas Pitre <nicolas.pitre@...aro.org>
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>,
	Ben Dooks <ben-linux@...ff.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>,
	Tarek Dakhran <t.dakhran@...sung.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-samsung-soc@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Mike Turquette <mturquette@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Naour Romain <romain.naour@...nwide.fr>,
	linux-arm-kernel@...ts.infradead.org,
	Heiko Stuebner <heiko@...ech.de>
Subject: Re: [PATCH 3/6] ARM: EXYNOS: add Exynos Dual Cluster Support

On Tue, Oct 01, 2013 at 03:55:24PM -0400, Nicolas Pitre wrote:
> On Tue, 1 Oct 2013, Vyacheslav Tyrtov wrote:
> 
> > From: Tarek Dakhran <t.dakhran@...sung.com>

[...]

> > +	kfs_use_count[cpu][cluster]++;
> > +	if (kfs_use_count[cpu][cluster] == 1) {
> > +		++core_count[cluster];
> > +		if (core_count[cluster] == 1) {
> > +			ret = exynos_cluster_power_up(cluster);
> > +			if (ret) {
> > +				pr_err("%s: cluster %u power up error\n",
> > +					__func__, cluster);
> > +				return ret;
> > +			}
> > +			__cci_control_port_by_index(MAX_NR_CLUSTERS
> > +					 - cluster, true);
> 
> This is wrong and very racy.  The state machine implemented in 
> mcpm-head.S is there already to handle proper synchronization for you.  

Maybe this issue didn't make itself obvious yet due to the lack of
suspend support.

Moving the CCI maintenance to power_up_setup() is essential for suspend/
resume to work, because then CPUs can power up randomly in response to
interrupts -- exynos_lock is not sufficient protection in that case.

The TC2 code should provide a good example of what to do.

[...]

Cheers
---Dave
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