LXR linux/Documentation/ABI/testing/sysfs-firmware-memmap

   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