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diff --git a/Documentation/ABI/testing/sysfs-firmware-dmi-entries b/Documentation/ABI/testing/sysfs-firmware-dmi-entries new file mode 100644 index 000000000..fe0289c87 --- /dev/null +++ b/Documentation/ABI/testing/sysfs-firmware-dmi-entries @@ -0,0 +1,114 @@ +What: /sys/firmware/dmi/entries/ +Date: February 2011 +Contact: Mike Waychison <mikew@google.com> +Description: + Many machines' firmware (x86 and ia64) export DMI / + SMBIOS tables to the operating system. Getting at this + information is often valuable to userland, especially in + cases where there are OEM extensions used. + + The kernel itself does not rely on the majority of the + information in these tables being correct. It equally + cannot ensure that the data as exported to userland is + without error either. + + DMI is structured as a large table of entries, where + each entry has a common header indicating the type and + length of the entry, as well as a firmware-provided + 'handle' that is supposed to be unique amongst all + entries. + + Some entries are required by the specification, but many + others are optional. In general though, users should + never expect to find a specific entry type on their + system unless they know for certain what their firmware + is doing. Machine to machine experiences will vary. + + Multiple entries of the same type are allowed. In order + to handle these duplicate entry types, each entry is + assigned by the operating system an 'instance', which is + derived from an entry type's ordinal position. That is + to say, if there are 'N' multiple entries with the same type + 'T' in the DMI tables (adjacent or spread apart, it + doesn't matter), they will be represented in sysfs as + entries "T-0" through "T-(N-1)": + + Example entry directories:: + + /sys/firmware/dmi/entries/17-0 + /sys/firmware/dmi/entries/17-1 + /sys/firmware/dmi/entries/17-2 + /sys/firmware/dmi/entries/17-3 + ... + + Instance numbers are used in lieu of the firmware + assigned entry handles as the kernel itself makes no + guarantees that handles as exported are unique, and + there are likely firmware images that get this wrong in + the wild. + + Each DMI entry in sysfs has the common header values + exported as attributes: + + ======== ================================================= + handle The 16bit 'handle' that is assigned to this + entry by the firmware. This handle may be + referred to by other entries. + length The length of the entry, as presented in the + entry itself. Note that this is _not the + total count of bytes associated with the + entry. This value represents the length of + the "formatted" portion of the entry. This + "formatted" region is sometimes followed by + the "unformatted" region composed of nul + terminated strings, with termination signalled + by a two nul characters in series. + raw The raw bytes of the entry. This includes the + "formatted" portion of the entry, the + "unformatted" strings portion of the entry, + and the two terminating nul characters. + type The type of the entry. This value is the same + as found in the directory name. It indicates + how the rest of the entry should be interpreted. + instance The instance ordinal of the entry for the + given type. This value is the same as found + in the parent directory name. + position The ordinal position (zero-based) of the entry + within the entirety of the DMI entry table. + ======== ================================================= + + **Entry Specialization** + + Some entry types may have other information available in + sysfs. Not all types are specialized. + + **Type 15 - System Event Log** + + This entry allows the firmware to export a log of + events the system has taken. This information is + typically backed by nvram, but the implementation + details are abstracted by this table. This entry's data + is exported in the directory:: + + /sys/firmware/dmi/entries/15-0/system_event_log + + and has the following attributes (documented in the + SMBIOS / DMI specification under "System Event Log (Type 15)": + + - area_length + - header_start_offset + - data_start_offset + - access_method + - status + - change_token + - access_method_address + - header_format + - per_log_type_descriptor_length + - type_descriptors_supported_count + + As well, the kernel exports the binary attribute: + + ============= ==================================== + raw_event_log The raw binary bits of the event log + as described by the DMI entry. + ============= ==================================== |