linux-kernel - Re: [PATCH v2 1/4] arm64, thunder: Add Kconfig option for Cavium Thunder SoC Family

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Message-ID: <20140905092507.GH13515@arm.com>
Date:	Fri, 5 Sep 2014 10:25:08 +0100
From:	Will Deacon <will.deacon@....com>
To:	Robert Richter <rric@...nel.org>
Cc:	Mark Rutland <Mark.Rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Radha Mohan Chintakuntla <rchintakuntla@...ium.com>,
	Olof Johansson <olof@...om.net>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Robert Richter <rrichter@...ium.com>
Subject: Re: [PATCH v2 1/4] arm64, thunder: Add Kconfig option for Cavium
 Thunder SoC Family

On Fri, Sep 05, 2014 at 10:21:35AM +0100, Robert Richter wrote:
> On 05.09.14 09:39:32, Will Deacon wrote:
> > On Fri, Sep 05, 2014 at 08:46:42AM +0100, Robert Richter wrote:
> > > From: Radha Mohan Chintakuntla <rchintakuntla@...ium.com>
> > > 
> > > Increase maximum numbers of cpus to 32. This relates to current
> > > maximal possible cpu number. Increasing this to 64 cpus will be a
> > > separate patch not part of this enablement patches.
> > 
> > Just out of interest, does raising the current maximum limit actually break
> > any existing code? If not, then doing this as two patches doesn't seem worth
> > it.
> 
> Increasing to 64 should be fine from the perspective of cpu mask
> implementation. Memory foot print should be the same already as this
> uses long which is 64 bit. So this wouldn't hurt.
> 
> However, I felt a bit uncomfortable having a dependency here to
> enabling 64 cpus and getting this patch set upstream. Support for more
> than 32 cpus is not well tested yet and there still might be problems
> with e.g. interrupt delivery or topology.

All I mean is, if the kernel doesn't explode on existing systems by changing
the upper limit to 64, then we should do that. If you're not comfortable
that the Thunder code can handle that, then leave the thunder default as 32,
like you do in the current patch. It just seems odd not to change the
maximum number, since it's an arbitrary limit from my perspective.

Will
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