1What:		/sys/firmware/memmap/
2Date:		June 2008
3Contact:	Bernhard Walle <bernhard.walle@gmx.de>
4Description:
5		On all platforms, the firmware provides a memory map which the
6		kernel reads. The resources from that memory map are registered
7		in the kernel resource tree and exposed to userspace via
8		/proc/iomem (together with other resources).
9
10		However, on most architectures that firmware-provided memory
11		map is modified afterwards by the kernel itself, either because
12		the kernel merges that memory map with other information or
13		just because the user overwrites that memory map via command
14		line.
15
16		kexec needs the raw firmware-provided memory map to setup the
17		parameter segment of the kernel that should be booted with
18		kexec. Also, the raw memory map is useful for debugging. For
19		that reason, /sys/firmware/memmap is an interface that provides
20		the raw memory map to userspace.
21
22		The structure is as follows: Under /sys/firmware/memmap there
23		are subdirectories with the number of the entry as their name:
24
25			/sys/firmware/memmap/0
26			/sys/firmware/memmap/1
27			/sys/firmware/memmap/2
28			/sys/firmware/memmap/3
29			...
30
31		The maximum depends on the number of memory map entries provided
32		by the firmware. The order is just the order that the firmware
33		provides.
34
35		Each directory contains three files:
36
37		start	: The start address (as hexadecimal number with the
38			  '0x' prefix).
39		end	: The end address, inclusive (regardless whether the
40			  firmware provides inclusive or exclusive ranges).
41		type	: Type of the entry as string. See below for a list of
42			  valid types.
43
44		So, for example:
45
46			/sys/firmware/memmap/0/start
47			/sys/firmware/memmap/0/end
48			/sys/firmware/memmap/0/type
49			/sys/firmware/memmap/1/start
50			...
51
52		Currently following types exist:
53
54		  - System RAM
55		  - ACPI Tables
56		  - ACPI Non-volatile Storage
57		  - reserved
58
59		Following shell snippet can be used to display that memory
60		map in a human-readable format:
61
62		-------------------- 8< ----------------------------------------
63		  #!/bin/bash
64		  cd /sys/firmware/memmap
65		  for dir in * ; do
66		      start=$(cat $dir/start)
67		      end=$(cat $dir/end)
68		      type=$(cat $dir/type)
69		      printf "%016x-%016x (%s)\n" $start $[ $end +1] "$type"
70		  done
71		-------------------- >8 ----------------------------------------
72