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

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:

quoted

On Tue, Jul 26, 2016 at 05:02:06PM +0900, AKASHI Takahiro wrote:

quoted

From: James Morse <redacted>

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 <redacted>
[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 <redacted>
---
 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.

quoted

quoted

+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

quoted

Why has PPC not need this and ARM does? 

quoted

+	};
+};
+
+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