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

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

[AKASHI Takahiro]

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
+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>;
+	};
+};
+
+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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Re: [PATCH v23 9/9] Documentation: dt: chosen properties for arm64 kdump

[Rob Herring]

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

[AKASHI Takahiro]

Rob,

On Thu, Jul 28, 2016 at 04:55:11PM +0900, AKASHI Takahiro wrote:
> Rob,
> 
> On Wed, Jul 27, 2016 at 10:09:33AM -0500, Rob Herring wrote:
> > 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.
> 
> Yeah, I will remove "user-space"-related description as Mark also
> commented before.
> 
> > > +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?
> 
> Please see:
> http://lists.infradead.org/pipermail/linux-arm-kernel/2016-July/443225.html
> 
> There was also a discussion that simply appending "mem=", or more generally
> any parameter, to a command line might break some assumption of order of
> parameters in the future.
> So adding a DT property would be a better way.

Do you have any other comments about those properties?

-Takahiro AKASHI

> Thanks,
> -Takahiro AKASHI
> 
> > 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
> > >