Hostboot

Hostboot firmware initializes all processor, bus, and memory within IBM POWER based systems. Furthermore, it is responsible for loading the hostboot image using hostboot bootloader, prepare hardware to load and run an appropriate payload (e.g phyp or skiboot), and provide runtime services while the payload is running. Various hostboot features are easily configurable via compile time CONFIG flags.

How to compile hostboot?

• Standalone compile:
  • cd hostboot
  • ./hb workon
  • make -j32
    • NOTE: You can run make clobber when switching between branches or releases for a fresh start
  • hb prime
• In OpenPOWER context:
  • op-build <system_name>_defconfig && op-build hostboot-rebuild machine-xml-rebuild openpower-pnor-rebuild
    • Example: op-build witherspoon_defconfig && op-build hostboot-rebuild machine-xml-rebuild openpower-pnor-rebuild
  • NOTE: Above command is assuming you have already done a full op-build compile already. If not, then run the following op-build <system_name>_defconfig && op-build

Various Components

Hostboot Bootloader (HBBL)

Hostboot Bootloader image is part of the SEEPROM SBE (Self Boot Engine) image. In istep 5.1, SBE loads the bootloader in cache. In istep 5.2, SBE starts instructions on the processor from where the HBBL is loaded. HBBL finds the hostboot images in pnor, loads them into memory, and starts hostboot.

Kernel

Hostboot uses a custom kernel that enables execution of user-space hostboot IPL firmware and services. The kernel provides the general execution environment, message passing, task control, memory management, interrupt support, and any other functions to support the initialization activities of the user space. It is a micro-kernel that pushes as much function as possible to the user space, which has more safety protections.

User Space Applications

There are various user space applications, including, device drivers, services necessary for base enablement, and other interactions with other components.

Device Drivers

• Base Device Driver FW (devicefw)
• FSI
• GPIO
• I2C
• SCAN/SCOM/IBSCOM/FSISCOM/XSCOM
• LPC
• MBOX
• PNOR

Base Services

• Error Logs
• Targeting
• FAPI2
• HWAS
• Base IPL Service (initservice/isteps)
• Interrupt Service
• Trace
• VFS
• VPD
• Console
• Secureboot

Other FW Components

• SBE
• HDAT
• HTMGT
• PRD/DIAGNOSTICS
• HBRT

Build

This contains all the infrastructure to compile, link, and generate hostboot binaries (including a full pnor for standalone compile).

Import

This contains code which does all the hardware accesses required to initialize the hardware. This lives in the import directory because we directly consume it from the hardware team and call it hardware procedures.