Chrome's Coreboot Firmware Adapting For 64-bit Boot, Prepping For Intel Panther Lake

The Open-Source Firmware Foundation is out with an interesting blog post by Google firmware engineer Subrata Banik around adapting the Coreboot-based Chrome AP Firmware for 64-bit booting. The transition to 64-bit booting is happening for the system firmware powering Chromebooks and other Chrome devices and is driven in part for Intel Panther Lake generation hardware.

Google engineers have been working on transitioning the Chrome firmware to using 64-bit mode during the boot/initialization process. There is a slight increase to the SPI flash size when moving from 32-bit to 64-bit boot but their analysis so far shows it being feasible.

Driving at least part of their motivation to 64-bit booting is for dealing with more than 4GB of memory with increasing hardware resource needs "due to recent developments in Intel SoC architecture." In particular, the blog post makes multiple references to needs with Intel Panther Lake SoCs that will succeed Lunar Lake in mid-2025. With most Coreboot ports still operating in 32-bit mode, making sure everything works well in 64-bit mode has been a large undertaking. Banik noted:

"The rationale behind supporting x86_64 boot mode for future Intel SoC platforms is to ensure that hardware resources can be accessed without limitations. Therefore, the goal of AP Firmware used across ChromeOS devices is more ambitious than the current offerings of coreboot regarding x86_64 support."

Google engineers have successfully tested using 64-bit mode for Coreboot, the Intel FSP, libpayload, and depthcharge codebases and then booting into ChromeOS. This 64-bit boot flow has been tested on real hardware and seems to be moving along nicely, presumably for a production deployment coming next year with Intel Panther Lake powered Chromebooks.

Those wanting to learn more about this x86_64 firmware boot undertaking can learn more via the post on the Open-Source Firmware Foundation blog.