| Bernhard Walle | 69ac9cd | 2008-06-27 13:12:54 +0200 | [diff] [blame] | 1 | What: /sys/firmware/memmap/ |
| 2 | Date: June 2008 |
| 3 | Contact: Bernhard Walle <bwalle@suse.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 ---------------------------------------- |