projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 863ef5ba | 1 | What: /sys/firmware/dmi/entries/ |
| 9effd822 MW |
2 | Date: February 2011 |
| 3 | Contact: Mike Waychison <mikew@google.com> | |
| 4 | Description: | |
| 5 | Many machines' firmware (x86 and ia64) export DMI / | |
| 6 | SMBIOS tables to the operating system. Getting at this | |
| 7 | information is often valuable to userland, especially in | |
| 8 | cases where there are OEM extensions used. | |
| 9 | ||
| 10 | The kernel itself does not rely on the majority of the | |
| 11 | information in these tables being correct. It equally | |
| 12 | cannot ensure that the data as exported to userland is | |
| 13 | without error either. | |
| 14 | ||
| 15 | DMI is structured as a large table of entries, where | |
| 16 | each entry has a common header indicating the type and | |
| 695cca87 MW |
17 | length of the entry, as well as a firmware-provided |
| 18 | 'handle' that is supposed to be unique amongst all | |
| 19 | entries. | |
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20 | |
| 21 | Some entries are required by the specification, but many | |
| 22 | others are optional. In general though, users should | |
| 23 | never expect to find a specific entry type on their | |
| 24 | system unless they know for certain what their firmware | |
| 695cca87 | 25 | is doing. Machine to machine experiences will vary. |
| 9effd822 MW |
26 | |
| 27 | Multiple entries of the same type are allowed. In order | |
| 28 | to handle these duplicate entry types, each entry is | |
| 29 | assigned by the operating system an 'instance', which is | |
| 30 | derived from an entry type's ordinal position. That is | |
| 31 | to say, if there are 'N' multiple entries with the same type | |
| 32 | 'T' in the DMI tables (adjacent or spread apart, it | |
| 33 | doesn't matter), they will be represented in sysfs as | |
| 34 | entries "T-0" through "T-(N-1)": | |
| 35 | ||
| 36 | Example entry directories: | |
| 37 | ||
| 38 | /sys/firmware/dmi/entries/17-0 | |
| 39 | /sys/firmware/dmi/entries/17-1 | |
| 40 | /sys/firmware/dmi/entries/17-2 | |
| 41 | /sys/firmware/dmi/entries/17-3 | |
| 42 | ... | |
| 43 | ||
| 44 | Instance numbers are used in lieu of the firmware | |
| 45 | assigned entry handles as the kernel itself makes no | |
| 46 | guarantees that handles as exported are unique, and | |
| 47 | there are likely firmware images that get this wrong in | |
| 48 | the wild. | |
| 49 | ||
| 50 | Each DMI entry in sysfs has the common header values | |
| 51 | exported as attributes: | |
| 52 | ||
| 53 | handle : The 16bit 'handle' that is assigned to this | |
| 54 | entry by the firmware. This handle may be | |
| 55 | referred to by other entries. | |
| 56 | length : The length of the entry, as presented in the | |
| 57 | entry itself. Note that this is _not the | |
| 58 | total count of bytes associated with the | |
| 59 | entry_. This value represents the length of | |
| 60 | the "formatted" portion of the entry. This | |
| 61 | "formatted" region is sometimes followed by | |
| 62 | the "unformatted" region composed of nul | |
| 63 | terminated strings, with termination signalled | |
| 64 | by a two nul characters in series. | |
| 65 | raw : The raw bytes of the entry. This includes the | |
| 66 | "formatted" portion of the entry, the | |
| 67 | "unformatted" strings portion of the entry, | |
| 68 | and the two terminating nul characters. | |
| 69 | type : The type of the entry. This value is the same | |
| 70 | as found in the directory name. It indicates | |
| 695cca87 | 71 | how the rest of the entry should be interpreted. |
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72 | instance: The instance ordinal of the entry for the |
| 73 | given type. This value is the same as found | |
| 74 | in the parent directory name. | |
| 695cca87 MW |
75 | position: The ordinal position (zero-based) of the entry |
| 76 | within the entirety of the DMI entry table. | |
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77 | |
| 78 | === Entry Specialization === | |
| 79 | ||
| 80 | Some entry types may have other information available in | |
| 695cca87 | 81 | sysfs. Not all types are specialized. |
| 9effd822 MW |
82 | |
| 83 | --- Type 15 - System Event Log --- | |
| 84 | ||
| 85 | This entry allows the firmware to export a log of | |
| 86 | events the system has taken. This information is | |
| 87 | typically backed by nvram, but the implementation | |
| 695cca87 | 88 | details are abstracted by this table. This entry's data |
| 9effd822 MW |
89 | is exported in the directory: |
| 90 | ||
| 91 | /sys/firmware/dmi/entries/15-0/system_event_log | |
| 92 | ||
| 93 | and has the following attributes (documented in the | |
| 94 | SMBIOS / DMI specification under "System Event Log (Type 15)": | |
| 95 | ||
| 96 | area_length | |
| 97 | header_start_offset | |
| 98 | data_start_offset | |
| 99 | access_method | |
| 100 | status | |
| 101 | change_token | |
| 102 | access_method_address | |
| 103 | header_format | |
| 104 | per_log_type_descriptor_length | |
| 105 | type_descriptors_supported_count | |
| 106 | ||
| 107 | As well, the kernel exports the binary attribute: | |
| 108 | ||
| 109 | raw_event_log : The raw binary bits of the event log | |
| 110 | as described by the DMI entry. |