[PATCH v31 12/12] Documentation: dt: chosen properties for arm64 kdump

[AKASHI Takahiro <takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

From: James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>

Add documentation for DT properties:
	linux,usable-memory-range
	linux,elfcorehdr
used by arm64 kdump. Those decribe the usable memory range for crash dump
kernel and the elfcorehdr's location within it, respectively.

Signed-off-by: James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>
[takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org: added "linux,crashkernel-base" and "-size" ]
Signed-off-by: AKASHI Takahiro <takahiro.akashi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Acked-by: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 Documentation/devicetree/bindings/chosen.txt | 37 ++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/Documentation/devicetree/bindings/chosen.txt b/Documentation/devicetree/bindings/chosen.txt
index 6ae9d82d4c37..8dc82431acc1 100644
--- a/Documentation/devicetree/bindings/chosen.txt
+++ b/Documentation/devicetree/bindings/chosen.txt
@@ -52,3 +52,40 @@ 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,usable-memory-range
+-------------------------
+
+This property (arm64 only) holds a base address and size, describing a
+limited region in which memory may be considered available for use by
+the kernel. Memory outside of this range is not available for use.
+
+This property describes a limitation: memory within this range is only
+valid when also described through another mechanism that the kernel
+would otherwise use to determine available memory (e.g. memory nodes
+or the EFI memory map). Valid memory may be sparse within the range.
+e.g.
+
+/ {
+	chosen {
+		linux,usable-memory-range = <0x9 0xf0000000 0x0 0x10000000>;
+	};
+};
+
+The main usage is for crash dump kernel to identify its own usable
+memory and exclude, at its boot time, any other memory areas that are
+part of the panicked kernel's memory.
+
+linux,elfcorehdr
+----------------
+
+This property (currently used only on arm64) holds the memory range,
+the address and the size, of the elf core header which mainly describes
+the panicked kernel's memory layout as PT_LOAD segments of elf format.
+e.g.
+
+/ {
+	chosen {
+		linux,elfcorehdr = <0x9 0xfffff000 0x0 0x800>;
+	};
+};
-- 
2.11.0

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