linux-kernel - Re: [PATCH 1/8] ARM: SCU: Add common routines for secondary CPU bootup

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Message-ID: <20101202152428.GD10461@n2100.arm.linux.org.uk>
Date:	Thu, 2 Dec 2010 15:24:28 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Anton Vorontsov <avorontsov@...sta.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Srinidhi Kasagar <srinidhi.kasagar@...ricsson.com>,
	Tony Lindgren <tony@...mide.com>,
	Jamie Iles <jamie.iles@...ochip.com>,
	Colin Cross <ccross@...roid.com>, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, linux-tegra@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/8] ARM: SCU: Add common routines for secondary CPU
	bootup

On Thu, Dec 02, 2010 at 03:19:05PM +0000, Catalin Marinas wrote:
> On 1 December 2010 00:25, Russell King - ARM Linux
> <linux@....linux.org.uk> wrote:
> > On Tue, Nov 30, 2010 at 11:32:04PM +0000, Russell King - ARM Linux wrote:
> >> Note that I'll go with factoring this out into arch/arm/kernel/smp_scu.c
> >> for the time being, but I'm not convinced about the other parts yet.
> >
> > IOW, something like the attached.  I've gone a little further and removed
> > the now unnecessary scu_enable() and scu_get_core_count() global functions,
> > making scu_enable() static, and eliminating scu_get_core_count() entirely.
> 
> There is some benefit in leaving get_core_count() in the platform
> code. For example, the SCU on Cortex-A15 doesn't expose the core count
> register and we have to get it from somewhere else (for now from some
> L2 cache controller register but in the future it may be hardcoded,
> passed via FDT or simply trying to boot maxcpus).

I notice that there's no way to tell what revision of SCU is implemented
on _any_ mpcore platform.

In light of that, I think there's no point what so ever trying to
consolidate this code - even the control register bits vary in
unpredictable ways between different MPcore implementations.

So we can't say "this is a SCU X and this is its register layout."

And really, having it undetectable except via DT (which from what I
can see, isn't happening any time soon) or via a command line argument
isn't acceptable.

So I think the idea of consolidating the SCU code is a lost cause.
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