Add README.md
Add a high level description of this repository.
Change-Id: I46c13a793fd552ce1039d338b758f7eb7fcfc40d
Signed-off-by: Jonathan Doman <jonathan.doman@intel.com>
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+# SMBIOS Parser
+
+The main application in this repo is `smbiosmdrv2app`, capable of parsing a
+binary [SMBIOS][1] table and publishing the system information on D-Bus, to be
+consumed by other OpenBMC applications.
+
+The SMBIOS table is usually sent to the BMC by the host firmware (BIOS). The
+system designer can theoretically choose any transport and mechanism for sending
+the SMBIOS data, but there are at least two implementation today:
+
+## MDRv2
+
+The primary API is a set of Intel OEM IPMI commands called Managed Data Region
+version 2 (MDRv2), which provides a means for host firmware to send data through
+the VGA shared memory region. MDRv2 has a concept of multiple agents, each
+maintaining a "directory" containing directory entries (aka data sets). The host
+can query for the existence and version of directories to determine when it
+needs to send an updated SMBIOS table.
+
+`intel-ipmi-oem` implements the [IPMI command handlers][2], routing commands and
+data to the correct agent (e.g. `smbios-mdr`). The [D-Bus interface][3] between
+the IPMI handler and `smbios-mdr` is largely a mirror of IPMI commands.
+
+## phosphor-ipmi-blobs
+
+[`phosphor-ipmi-blobs`][4] is an alternative implementation of a generic IPMI
+blob transfer API. Compared to MDRv2, it is simpler and easier to use, but also
+transfers the data in-band with the IPMI commands and therefore slower than
+using a shared memory region (which may or may not be a concern).
+
+`phosphor-ipmi-blobs` provides a blob manager shared library for `ipmid` which
+implements the IPMI commands. In turn, it loads blob handler libraries that each
+implement support for specific blobs. Here in `smbios-mdr` we provide such a
+blob handler for the `/smbios` blob. It works by writing the data into
+`/var/lib/smbios/smbios2` (the local persistent cache for the SMBIOS table) and
+calling the `AgentSynchronizeData` D-Bus method to trigger `smbios-mdr` to
+reload and parse the table from that file.
+
+# Intel CPU Info
+
+`cpuinfoapp` is an Intel-specific application that uses I2C and PECI to gather
+more details about Xeon CPUs that aren't included in the SMBIOS table for some
+reason. It also implements discovery and control for Intel Speed Select
+Technology (SST).
+
+[1]: https://www.dmtf.org/standards/smbios
+[2]:
+ https://github.com/openbmc/intel-ipmi-oem/blob/84c203d2b74680e9dd60d1c48a2f6ca8f58462bf/src/smbiosmdrv2handler.cpp#L1272
+[3]:
+ https://github.com/openbmc/phosphor-dbus-interfaces/blob/d1484a1499bc241316853934e6e8b735166deee2/yaml/xyz/openbmc_project/Smbios/MDR_V2.interface.yaml
+[4]: https://github.com/openbmc/phosphor-ipmi-blobs