Re: [PATCH 9/9] arm64: Add new cpu-return-addr device tree binding

[Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>]

On Fri, Aug 22, 2014 at 08:49:17PM +0100, Geoff Levand wrote:
> Add a new arm64 device tree binding cpu-return-addr.  This binding is recomended
> for all ARM v8 CPUs that have an "enable-method" property value of "spin-table".
> The value is a 64 bit physical address that secondary CPU execution will transfer
> to upon CPU shutdown.
> 
> Signed-off-by: Geoff Levand <geoff-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/arm/cpus.txt | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/cpus.txt b/Documentation/devicetree/bindings/arm/cpus.txt
> index 1fe72a0..42d5d5f 100644
> --- a/Documentation/devicetree/bindings/arm/cpus.txt
> +++ b/Documentation/devicetree/bindings/arm/cpus.txt
> @@ -201,6 +201,15 @@ nodes to be present and contain the properties described below.
>  			  property identifying a 64-bit zero-initialised
>  			  memory location.
>  
> +	- cpu-return-addr
> +		Usage: recomended for all ARM v8 CPUs that have an
> +		       "enable-method" property value of "spin-table".
> +		Value type: <prop-encoded-array>
> +		Definition:
> +			# On ARM v8 64-bit systems must be a two cell property.
> +			The value is a 64 bit physical address that secondary
> +			CPU execution will transfer to upon CPU shutdown.

As I've been away for most of the past four weeks, I haven't read all
the threads around this topic. But I don't think we ended up with a
clearly agreed recommendation for cpu-return-addr. If we do, we also
need to be clear on what state the CPU should be in when returned to
such address (ELx, MMU, caches).

In general, if we need returning to firmware I would strongly recommend
PSCI but I know there is the Applied board which does not have EL3, so
something like this may work. But we need to get them into discussion as
well since I assume cpu-return-addr would be a firmware provided
address.

-- 
Catalin
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