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   1 What:           /sys/firmware/memmap/
   2 Date:           June 2008
   3 Contact:        Bernhard Walle <bernhard.walle@gmx.de>
   4 Description:
   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 ----------------------------------------