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		========  =====================================================
38		start	  The start address (as hexadecimal number with the
39			  '0x' prefix).
40		end	  The end address, inclusive (regardless whether the
41			  firmware provides inclusive or exclusive ranges).
42		type	  Type of the entry as string. See below for a list of
43			  valid types.
44		========  =====================================================
45
46		So, for example::
47
48			/sys/firmware/memmap/0/start
49			/sys/firmware/memmap/0/end
50			/sys/firmware/memmap/0/type
51			/sys/firmware/memmap/1/start
52			...
53
54		Currently following types exist:
55
56		  - System RAM
57		  - ACPI Tables
58		  - ACPI Non-volatile Storage
59		  - Unusable memory
60		  - Persistent Memory (legacy)
61		  - Persistent Memory
62		  - Soft Reserved
63		  - reserved
64
65		Following shell snippet can be used to display that memory
66		map in a human-readable format::
67
68		  #!/bin/bash
69		  cd /sys/firmware/memmap
70		  for dir in * ; do
71		      start=$(cat $dir/start)
72		      end=$(cat $dir/end)
73		      type=$(cat $dir/type)
74		      printf "%016x-%016x (%s)\n" $start $[ $end +1] "$type"
75		  done
76