EBBR Notes 2024.10.23

Attendees

• Heinrich Schuchardt (Canonical)
• Jon Humphreys (TI)
• Rob Herring (Arm)
• Etienne Carrière (STMicroelectronics)
• Vincent Stehlé (Arm)

Agenda

• Pull request #132 Boot Manager requirements
• Pull request #134 Recommend psci node under firmware

Notes

• Pull request #134 lead to discussions; components such as U-Boot, OP-TEE, TF-A and Qemu are concerned. More validation is needed before adding the recommendation.
• Pull request #132 approved, to be merged.

Raw notes

• Pull request #134 Recommend psci node under firmware
  • Why not "just" update the schemas and tools to complain when /psci is not under /firmware ? The drivers could still deal happily with legacy systems with /psci under /
  • Why do we care about where it is exactly?
  • Recommendation: under /firmware for new designs but do not fix old ones.
  • Deal with tooling after decision (SystemReady or else)
  • OP-TEE can generate the node; are Kernel and U-Boot able to deal with the new path?
  • TI platforms have /psci under /firmware; this validates that Linux can deal with that at least
    • And U-Boot, too
      • Reset works on TI platforms
    • How about OP-TEE?
    • If you put it under /foo with no property in it (ex: no compatible), it would not work
    • /firmware has no compatible
    • (From kernel point of view) would work anywhere
    • OP-TEE generates the node, does not use it
    • U-Boot will generate at the root
    • If exists: not modified, otherwise generated, for U-Boot & OP-TEE
    • Check only for /psci under root node / today
    • The recommendation would imply a code change in U-Boot and OP-TEE
    • TF-A has platforms where the dts/dtb is data; can it generate the /psci node?
    • Qemu generates the Devicetree, too
      • Would probably reject the change, based on past experiences
    • U-Boot accepts an existing /psci node anywhere
  • -> Let's validate a bit more before adding the recommendation
  • (and let's fix SystemReady tools)
  • Code references
    • For u-boot: u-boot/arch/arm/lib/psci-dt.c
    • For OP-TEE: dt_add_psci_node() in core/arch/arm/kernel/boot.c
    • Qemu: hw/arm/boot.c:472: qemu_fdt_add_subnode(fdt, "/psci");
    • U-Boot looks under root: rc = fdt_path_offset(fdt, "/psci");
    • U-Boot is not looking for compatible string.
• Pull request #132 Boot Manager requirements
  • Looks good, could be merged
  • More information than previously
  • Canonical investigating HTTP boot with GRUB, too
  • GRUB has a (slow) TCP stack
  • U-Boot knows to do HTTP boot with a Boot Option (short form URI)
  • -> merge

Links

• https://github.com/ARM-software/ebbr/pull/132
• https://github.com/ARM-software/ebbr/pull/134
• https://source.denx.de/u-boot/u-boot/-/blob/master/arch/arm/lib/psci-dt.c?ref_type=heads
• https://github.com/OP-TEE/optee_os/blob/master/core/arch/arm/kernel/boot.c
• https://gitlab.com/qemu-project/qemu/-/blob/master/hw/arm/boot.c?ref_type=heads#L472
• https://gitlab.arm.com/systemready/systemready-scripts