Known NVRAM settings in Skiboot
A loose collection of known NVRAM settings in Skiboot. These should eventually be exposed via the Petiboot TUI.
To query the state of these settings, execute the following from the petitboot shell, or from a host OS with the nvram utility installed:
nvram -p ibm,skiboot --print-config
Enable quick return to petitboot on reset
On Talos II firmware v2.00+ from RCS, and all Blackbird firmwares from RCS, fast reset is enabled by default. Instead of cycling host power and running the entire IPL process when the system reboots, Skiboot simply re-executes the Skiroot kernel, which runs petitboot to re-launch the host OS. However, certain devices/drivers (most often GPUs with dynamically-loaded firmware) may misbehave when the OS is reloaded without a host power cycle; thus, it may be beneficial to disable this behavior. Set to 1 to enable, or 0 to disable.
nvram -p ibm,skiboot --update-config fast-reset=0
PCIe Link Speed Cap
To cap the link speed, change the "pcie-max-link-speed" variable to the maximum generation you want to support and re-IPL the machine. For instance, to cap at PCIe Generation 3, in the petitboot command line type:
nvram -p ibm,skiboot --update-config pcie-max-link-speed=3
Skiroot kernel command line parameters
Controls the arguments passed to the skiroot kernel. For example, to prevent petitboot from appearing on the AST video output and prefer another GPU if available:
nvram -p ibm,skiboot --update-config bootargs='modprobe.blacklist=ast'
Enable the Virtual Accelerator Switchboard (VAS) userspace support
This allows Linux 5.8 and up to interact with the VAS, which is currently used to provide a userspace interface to the nx-gzip accelerator. Note that this option requires skiboot 6.6 or newer, which is not currently shipped by any RCS firmware release.
nvram -p ibm,skiboot --update-config vas-user-space=enable