systemd-boot support and L4TLauncher

[igoropaniuk]

I've stumbled upon multiple discussions here about integration of systemd-boot and currently trying to bring up a PoC setup, so we can replace syslinux.cfg and have a generic EFI boot loader mechanism supporting UEFI secure boot, UKIs and so on.

IIUC for now the only supported boot sequence is EDK2 -> L4TLauncher -> systemd-boot, as we have to keep L4TLauncher, because it handles Tegra-specific (so-called "boot chains") A/B redundancy implementation (btw, is there any else I might have missed in L4TLauncher sources that might be useful for Linux booting?).

I was wondering if it's possible ti get rid of L4TLauncher completely, and have systemd-boot as default boot file EFI/BOOT/BOOTAA64.efi. EDK2 BootChainDxe driver instead of setting EFI variables BootChainFwCurrent/BootChainOsCurrent can directly "flip" boot entries (considering we have entries like default-slot.conf and fallback-slot.conf) in ESP partition. I'm not sure if it's a good idea, but I haven't found any restrictions in UEFI PI spec

[dwalkes]

I was wondering if it's possible to get rid of L4TLauncher completely,

I don't have any direct knowledge in this area but there is also a discussion about using grub instead of L4TLauncher at #1480 if you haven't found this already. Perhaps this implementation could be useful to figure out how to replace l4tlauncher in a systemd-boot scheme.

[dwalkes]

This was briefly discussed in the meeting this month at https://github.com/OE4T/meta-tegra/wiki/OE4T-Meeting-Notes-2024%E2%80%9009%E2%80%9012 as well (see the end of the meeting)