linux-kernel - Re: [PATCH 2/3] ARM: dts: document the berlin enable-method property

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Message-ID: <20140403090247.GM16420@e106331-lin.cambridge.arm.com>
Date:	Thu, 3 Apr 2014 10:02:47 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Antoine Ténart 
	<antoine.tenart@...e-electrons.com>
Cc:	"sebastian.hesselbarth@...il.com" <sebastian.hesselbarth@...il.com>,
	"zmxu@...vell.com" <zmxu@...vell.com>,
	"jszhang@...vell.com" <jszhang@...vell.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"alexandre.belloni@...e-electrons.com" 
	<alexandre.belloni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/3] ARM: dts: document the berlin enable-method
 property

On Thu, Apr 03, 2014 at 09:08:15AM +0100, Antoine Ténart wrote:
> Signed-off-by: Antoine Ténart <antoine.tenart@...e-electrons.com>
> ---
>  Documentation/devicetree/bindings/arm/cpus.txt | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
> index 333f4aea3029..a9e42a2dbc99 100644
> --- a/Documentation/devicetree/bindings/arm/cpus.txt
> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> @@ -185,6 +185,8 @@ nodes to be present and contain the properties described below.
>  			    "qcom,gcc-msm8660"
>  			    "qcom,kpss-acc-v1"
>  			    "qcom,kpss-acc-v2"
> +			    "marvell,88de31-smp" - cpu-core handling for Berlin
> +					SoC from Marvell starting with 88de31

It would probably be best to add an enable-method directory and document
what each of these mean (what's expected of the platform, what steps an
OS should make to bring up and/or tear down CPUs).

While it's nice to factor this out of the kernel, I'd like this to be
better-defined such that it's clear what the expectations of each
enable-method are. That ways it iss possible for OSs other than Linux to
make use of the enable-method information (as it won't be an opaque
reference to Linux internals), and we can have a clear definition of
each enable-method independent of any implementation details.

Going forward I would like to see fewer implementation-specific
protocols for bringing up secondaries, and a move to fewer more
standardised mechanisms like PSCI. I realise that might not be possible
in all cases, but it would be nice to avoid a proliferation of
enable-methods with single users.

Cheers,
Mark.
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