I hadn’t even finished writing up the 1.6 related artifacts when Pete pushed the button on the new release. Huge thanks both to Pete for getting this out there so soon and to Ard Biesheuvel for reviewing and approving the edk2-platforms fixes.
The ACPI fixes will mean improved hardware support in OSes, although today that mostly means improved NetBSD support. We definitely need some volunteers to help with enabling Pi 4 support with ACPI in upstream Linux – see the issue tracker.
Big shout-out to Jeremy Linton for the PPTT implementation (Processor Properties Topology Table) – a new ACPI 6.3 table describing the relation between CPUs and caches. Yes, that’s not a typo – our PPTT is the 2nd revision variant introduced in ACPI 6.3, whereas PPTT was first introduced in 6.2.
Biggest change here is that your Pi will now boot at the default (Pi Foundation-recommended) frequency, instead of the 600MHz minimum. One less configuration option to change on every upgrade!
IMPORTANT: HTTP(S) boot, like PXE and iSCSI, will not currently work with the internal network card, because the GENET driver has not been upstreamed yet. This means you need a supported USB interface (Ax88772b) to use this feature.
This release mostly improves on the logic added to v1.4 release for switching between 3GB/4GB modes on the 4GB Pi 4.
The fix for external .dtb is worth diving into. Many of our readers will know, that Raspberries traditionally boot operating systems with Device Tree, instead of ACPI. A dated overview can be found on the official Pi site. Long story short, if you want to boot an 64-bit Linux, NetBSD or FreeBSD today on the Pi with full I/O support, you still need the Device Tree that the VPU firmware prepares based on your config.txt settings (dtparams, overlays, etc).
The Pi 4 support for Device Tree is exactly like the Pi 3 support. At the time, UEFI relied on the Device Tree being placed in RAM after the UEFI image itself, basically overlaying itself on a section of the UEFI image. Recently, new VideoCore firmware broke this approach (which I really shouldn’t have come up with in the first place!) by switching the load ordering – now the Device Tree was loaded before the UEFI image, and since the two images overlapped, the Device Tree blob was getting overwritten. You can read more about it here and here. Anyway, it’s fixed now. The same fix needs to be made to the Pi 3 build. That’s still TBD.
Be mindful that the fix involved changing the load address for the Device Tree in a way that wouldn’t overlap the UEFI image. The new values are:
While looking at the above regression, we were also able to regain 2MiB of memory, as the Trusted Firmware footprint for Pi 4 is much smaller than on the Pi 3.
It may not look like much, but it provides a radically improved networking experience, courtesy of a heads up by Jared and his recent work on the NetBSD GENET driver.
Of course what use is improved GENET via ACPI, when there is barely an OS support? Well, courtesy of the amazing work done by Pete and Jeremy Linton, the Linux ACPI patch for GENET has been merged into net-next.
Courtesy of Pete Batard, a new release is out. Again, this is very early in development, so the usual caveats apply – not all OSes will behave as expected and there’s not much yet in terms of step-by-step instructions.