The bl31.bin TF-A binary found in this directory was built from the
official TF-A 2.9 release
through a GitHub build script
that is designed to provide evidence that these binaries match the vanilla TF-A source.
Per the GitHub Actions log, the SHA-256 sum for the bin can be validated to be as follows:
bl31.bin:681afd3c044ad0020c3182e9f7a8d43f726ab19467dba2db8086bb41f3e4b521
For Raspberry Pi 4 usage, TF-A was built using the command:
make PLAT=rpi4 RPI3_PRELOADED_DTB_BASE=0x1F0000 PRELOADED_BL33_BASE=0x20000 SUPPORT_VFP=1 SMC_PCI_SUPPORT=1 DEBUG=0 all