So, the Pi 3A+ is finally documented as being supported. It involved no code changes and is the cheapest Pi you can run the 64-bit UEFI firmware on.
But there’s more – the work to automatically support booting via PL011 and miniUART serial ports, done by Pete Batard on the UEFI side and Andre Przywara for TF-A, finally means we can boot on boards where PL011 is used to expose the serial port. The Pi 2B (v1.2) is one such board – the slowest member of the 64-bit UEFI for Pi family. It’s basically a Pi 3 without WiFi, BT and worse heat dissipation, so it is clocked down.
And after fixing a small eMMC support regression, we even support the compute module variant of the Pi 3. To be fair, I didn’t test the CM3L (the one without eMMC), but it should be working. Let me know if it doesn’t. Also, CM3+ (which just has better heat dissipation) should work but is not validated.
And in case you’re a fan of the amazing cluster carrier board from our friends over at miniNodes…
Those last two fixed regressions seen on Windows 10 after some ACPI restructuring to properly describe DMA constraints on VideoCore-attached devices. The regressions affected Pi 3, but the fix should equally apply to Pi 4.
TF-A is the Arm secure firmware, providing services such as platform power off/reset and secondary CPU manipulation. The improvements to UART detection mean that TF-A firmware, just like UEFI, will honor config.txt selection of the UART (e.g. via overlay, although it’s really done by the VPU firmware). This is more developer oriented, and means not losing logging/initialization messages. Unrelated to Pi 4 itself, it paves the way for proper (transparent) Pi 3 UEFI support for Compute Module variants and that 64-bit variant of the Pi 2 (rev 1.2).
The Pi 3B/3B+ is still a great platform to explore UEFI functionality, and it’s EBBR-compliant UEFI boot for Linux (that is, with device tree) is still way better than messing with config files. Plus you can do PXE and iSCSI. Isn’t that awesome? Or port Doom to it :-).