OCSD

This crate provides utilities to enable reporting and monitoring of OCSD sensor values from the host OS.

Credit to ilo4_unlock which made this reverse-engineering effort possible.

Disclaimer

Protocol documentation for OCSD is not publicly available. All of this has been reverse-engineered from a single ML350 Gen9. It has not been tested on any other hardware! I cannot guarantee that it fully complies with the OCSD protocol, and results on your server may vary.

What's OCSD?

Some HPE servers from Gen8 onwards are equipped with a feature called Option Card Sensor Data (OCSD), also referred to as "Sea of Sensors". OCSD allows temperature data to be sent from option cards (e.g. RAID controller daughterboards, PCIe expansion cards) to iLO/BIOS for fan control and monitoring.

OK, cool, so why do we need this crate?

Ordinarily, supported option cards will directly report temperatures via OCSD without any involvement from the host OS, and the server will respond by controlling the fans accordingly.

In the case of unsupported option cards, the server may do one of the following:

• Assume that the card is running very hot and spin up the fans to deafening levels at all times
• Ignore the card's existence entirely. In the case of passively cooled cards (e.g. unsupported server GPUs), this leads to thermal throttling due to insufficient fan speed at high load.

Ideally, when installing an unsupported option card, we would just modify its firmware to report temperatures directly to the OCSD buffer. Unfortunately, this would be really difficult.

As an alternative, this crate allows the host OS to take the reported temperatures available from existing drivers, and forward them to the OCSD buffer so they can be used by the iLO controller for reporting and fan control. It also allows for reading reported temperatures for supported devices directly out of the OCSD buffer, although there are probably better ways of getting that data.