Murata PSUs dislike IC_DEVICE_{ID, REV} - #39
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Closes #435 (which this obsoletes). This branch adds a new `component-get-vpd` RPC that allows MGS to read the vital product data (VPD) for the requested SP component. The SP components that have VPD advertise this property via the `HAS_VPD` capabilities bit. The wire types allow reading a few different kinds of VPD: - A variety of PMBus commands for PMBus devices. Hubris will determine which of the commands a given PMBus device supports based on oxidecomputer/pmbus#38 and oxidecomputer/pmbus#39. This is potentially quite large, but usually isn't, based on what the device actually supports. - An Oxide barcode from a VPD EEPROM, which may be in either the 0XV1, 0XV2, or MPN1 formats as defined in [RFD 308]. - A Gimlet or Cosmo fan tray EEPROM, which contains barcodes for the fan tray assembly, the VPD board, and each individual fan on the assembly. - A TMP117 temperature sensor's little EEPROM thingy. The way this all works is designed to allow Hubris to avoid constructing these on the stack. In particular, the fan tray VPD may be "up to 640 bytes or more", given that the only real length limit on the MPN1 barcodes is that the whole thing will not be in excess of 128 bytes, and we may have a fan tray whose EEPROM contains five MPN1 barcodes, which is a lot. The PMBus VPD is also Not Small. Therefore, all the wire types are designed in such a way so that Hubris can read data _into_ a single scratch instance of the wire type which lives in a static, and then serialize from that straight into the trailing data of a response. This felt like the best compromise between wanting to use `hubpack` for serialization and not building really giant structs on the stack in `control-plane-agent`. This all probably makes a bit more sense if you also read the corresponding Hubris PR oxidecomputer/hubris#2650. [RFD 308]: https://rfd.shared.oxide.computer/rfd/0308
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