1 What: /sys/firmware/dmi/entries/ 1 What: /sys/firmware/dmi/entries/
2 Date: February 2011 2 Date: February 2011
3 Contact: Mike Waychison <mikew@google.co 3 Contact: Mike Waychison <mikew@google.com>
4 Description: 4 Description:
5 Many machines' firmware (x86 a 5 Many machines' firmware (x86 and arm64) export DMI /
6 SMBIOS tables to the operating 6 SMBIOS tables to the operating system. Getting at this
7 information is often valuable 7 information is often valuable to userland, especially in
8 cases where there are OEM exte 8 cases where there are OEM extensions used.
9 9
10 The kernel itself does not rel 10 The kernel itself does not rely on the majority of the
11 information in these tables be 11 information in these tables being correct. It equally
12 cannot ensure that the data as 12 cannot ensure that the data as exported to userland is
13 without error either. 13 without error either.
14 14
15 DMI is structured as a large t 15 DMI is structured as a large table of entries, where
16 each entry has a common header 16 each entry has a common header indicating the type and
17 length of the entry, as well a 17 length of the entry, as well as a firmware-provided
18 'handle' that is supposed to b 18 'handle' that is supposed to be unique amongst all
19 entries. 19 entries.
20 20
21 Some entries are required by t 21 Some entries are required by the specification, but many
22 others are optional. In gener 22 others are optional. In general though, users should
23 never expect to find a specifi 23 never expect to find a specific entry type on their
24 system unless they know for ce 24 system unless they know for certain what their firmware
25 is doing. Machine to machine 25 is doing. Machine to machine experiences will vary.
26 26
27 Multiple entries of the same t 27 Multiple entries of the same type are allowed. In order
28 to handle these duplicate entr 28 to handle these duplicate entry types, each entry is
29 assigned by the operating syst 29 assigned by the operating system an 'instance', which is
30 derived from an entry type's o 30 derived from an entry type's ordinal position. That is
31 to say, if there are 'N' multi 31 to say, if there are 'N' multiple entries with the same type
32 'T' in the DMI tables (adjacen 32 'T' in the DMI tables (adjacent or spread apart, it
33 doesn't matter), they will be 33 doesn't matter), they will be represented in sysfs as
34 entries "T-0" through "T-(N-1) 34 entries "T-0" through "T-(N-1)":
35 35
36 Example entry directories:: 36 Example entry directories::
37 37
38 /sys/firmware/dmi/entr 38 /sys/firmware/dmi/entries/17-0
39 /sys/firmware/dmi/entr 39 /sys/firmware/dmi/entries/17-1
40 /sys/firmware/dmi/entr 40 /sys/firmware/dmi/entries/17-2
41 /sys/firmware/dmi/entr 41 /sys/firmware/dmi/entries/17-3
42 ... 42 ...
43 43
44 Instance numbers are used in l 44 Instance numbers are used in lieu of the firmware
45 assigned entry handles as the 45 assigned entry handles as the kernel itself makes no
46 guarantees that handles as exp 46 guarantees that handles as exported are unique, and
47 there are likely firmware imag 47 there are likely firmware images that get this wrong in
48 the wild. 48 the wild.
49 49
50 Each DMI entry in sysfs has th 50 Each DMI entry in sysfs has the common header values
51 exported as attributes: 51 exported as attributes:
52 52
53 ======== ==================== 53 ======== =================================================
54 handle The 16bit 'handle' t 54 handle The 16bit 'handle' that is assigned to this
55 entry by the firmwar 55 entry by the firmware. This handle may be
56 referred to by other 56 referred to by other entries.
57 length The length of the en 57 length The length of the entry, as presented in the
58 entry itself. Note 58 entry itself. Note that this is _not the
59 total count of bytes 59 total count of bytes associated with the
60 entry. This value r 60 entry. This value represents the length of
61 the "formatted" port 61 the "formatted" portion of the entry. This
62 "formatted" region i 62 "formatted" region is sometimes followed by
63 the "unformatted" re 63 the "unformatted" region composed of nul
64 terminated strings, 64 terminated strings, with termination signalled
65 by a two nul charact 65 by a two nul characters in series.
66 raw The raw bytes of the 66 raw The raw bytes of the entry. This includes the
67 "formatted" portion 67 "formatted" portion of the entry, the
68 "unformatted" string 68 "unformatted" strings portion of the entry,
69 and the two terminat 69 and the two terminating nul characters.
70 type The type of the entr 70 type The type of the entry. This value is the same
71 as found in the dire 71 as found in the directory name. It indicates
72 how the rest of the 72 how the rest of the entry should be interpreted.
73 instance The instance ordinal 73 instance The instance ordinal of the entry for the
74 given type. This va 74 given type. This value is the same as found
75 in the parent direct 75 in the parent directory name.
76 position The ordinal position 76 position The ordinal position (zero-based) of the entry
77 within the entirety 77 within the entirety of the DMI entry table.
78 ======== ==================== 78 ======== =================================================
79 79
80 **Entry Specialization** 80 **Entry Specialization**
81 81
82 Some entry types may have othe 82 Some entry types may have other information available in
83 sysfs. Not all types are spec 83 sysfs. Not all types are specialized.
84 84
85 **Type 15 - System Event Log** 85 **Type 15 - System Event Log**
86 86
87 This entry allows the firmware 87 This entry allows the firmware to export a log of
88 events the system has taken. 88 events the system has taken. This information is
89 typically backed by nvram, but 89 typically backed by nvram, but the implementation
90 details are abstracted by this 90 details are abstracted by this table. This entry's data
91 is exported in the directory:: 91 is exported in the directory::
92 92
93 /sys/firmware/dmi/entries/15 93 /sys/firmware/dmi/entries/15-0/system_event_log
94 94
95 and has the following attribut 95 and has the following attributes (documented in the
96 SMBIOS / DMI specification und 96 SMBIOS / DMI specification under "System Event Log (Type 15)":
97 97
98 - area_length 98 - area_length
99 - header_start_offset 99 - header_start_offset
100 - data_start_offset 100 - data_start_offset
101 - access_method 101 - access_method
102 - status 102 - status
103 - change_token 103 - change_token
104 - access_method_address 104 - access_method_address
105 - header_format 105 - header_format
106 - per_log_type_descriptor_leng 106 - per_log_type_descriptor_length
107 - type_descriptors_supported_c 107 - type_descriptors_supported_count
108 108
109 As well, the kernel exports th 109 As well, the kernel exports the binary attribute:
110 110
111 ============= ============ 111 ============= ====================================
112 raw_event_log The raw bina 112 raw_event_log The raw binary bits of the event log
113 as described 113 as described by the DMI entry.
114 ============= ============ 114 ============= ====================================
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