Re: [PATCH v23 9/9] Documentation: dt: chosen properties for arm64 kdump

[Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Tue, Jul 26, 2016 at 05:02:06PM +0900, AKASHI Takahiro wrote:
> From: James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>
> 
> Add documentation for
> 	linux,crashkernel-base and crashkernel-size,
> 	linux,usable-memory-range, and
> 	linux,elfcorehdr
> used by arm64 kexec/kdump to decribe the kdump reserved area, and
> the elfcorehdr's location within it.
> 
> Signed-off-by: James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>
> [takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org:
>     renamed "usable-memory" to "usable-memory-range",
>     added "linux,crashkernel-base" and "-size" ]
> Signed-off-by: AKASHI Takahiro <takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
>  Documentation/devicetree/bindings/chosen.txt | 45 ++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
> index 6ae9d82..d7a3a86 100644
> --- a/Documentation/devicetree/bindings/chosen.txt
> +++ b/Documentation/devicetree/bindings/chosen.txt
> @@ -52,3 +52,48 @@ This property is set (currently only on PowerPC, and only needed on
>  book3e) by some versions of kexec-tools to tell the new kernel that it
>  is being booted by kexec, as the booting environment may differ (e.g.
>  a different secondary CPU release mechanism)
> +
> +linux,crashkernel-base
> +linux,crashkernel-size
> +----------------------
> +These properties are set (on PowerPC and arm64) during kdump to tell
> +use-space tools, like kexec-tools, the base address of the crash-dump

s/use/user/

Ideally, userspace should not care whether this comes from DT, kernel 
command-line or somewhere else and should be exposed in some source 
independent way. However, that's not really the problem for the binding.

> +kernel's reserved area of memory and the size. e.g.
> +
> +/ {
> +	chosen {
> +		linux,crashkernel-base = <0x9 0xf0000000>;
> +		linux,crashkernel-size = <0x0 0x10000000>;
> +	};
> +};
> +
> +linux,usable-memory-range
> +-------------------------
> +
> +This property is set (currently only on arm64) during kdump to tell
> +the crash-dump kernel the base address of its reserved area of memory,
> +and the size. e.g.
> +
> +/ {
> +	chosen {
> +		linux,usable-memory-range = <0x9 0xf0000000 0x0 0x10000000>;

This is the same range as linux,crashkernel-*, but used by the 2nd 
kernel? Why not just update the memory node or use command line mem= 
parameter?

Why has PPC not need this and ARM does? 

> +	};
> +};
> +
> +Please note that, if this property is present, any memory regions under
> +"memory" nodes will be ignored.
> +
> +linux,elfcorehdr
> +----------------
> +
> +This property is set (currently only on arm64) during kdump to tell
> +the crash-dump kernel the address and size of the elfcorehdr that describes
> +the old kernel's memory as an elf file. This memory must reside within
> +the area described by 'linux,usable-memory-range'. e.g.
> +
> +/ {
> +	chosen {
> +		linux,usable-memory = <0x9 0xf0000000 0x0 0x10000000>;
> +		linux,elfcorehdr = <0x9 0xfffff000 0x0 0x800>;
> +	};
> +};
> -- 
> 2.9.0
> 
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