raspberryPi-*: unify Pi 3/4

[leo60228]

This unifies Pi 3 and Pi 4 to use a single binary, which as a side-effect makes #59 trivial. I've not tested this beyond building yet, and preferably it should be tested on every BCM2710/BCM2711 Pi board (but at least the 3B/3B+/4B).

[colemickens]

From:

https://patchwork.ozlabs.org/project/uboot/patch/20191106144104.28177-1-matthias.bgg@kernel.org/

Provide a defconfig which allows us to boot Raspberrry Pi 4
and Raspberry Pi 3 Model B/B+
Instead of using the embedded DTB as done in RPi3 we use the
devicetree provided by the firmware.

I am not sure I totally understand these implications.

Does this mean that the DTBs copied in with this PR are loaded by the rpi firmware and then provided to u-boot? What happens if they differ from the kernel?

When I built this, it booted my 5.13 extlinux entries but not the 5.14 or 5.15 entries. I'm still looking into it.

[colemickens]

Also, the dtbs in my extlinux dtbs dirs for the rpi3 are named differently than the commit targets.

bcm2837-rpi-3-b.dtb rather than bcm2710*.

[colemickens]

I guess this is copying dtbs from the rpi-firmware. Which from the patchwork thread, seems to be what happens when u-boot is embedding their own copy of the dtb anyway... :/

[colemickens]

Okay, my issue was because we need to port the updated 0001-configs-rpi-allow-for-bigger-kernels.patch in from nixpkgs. This PR seems to boot my rpi4 at least.

[colemickens]

Okay, now that I've tested this with the larger kernel, and I've reviewed the notes about this defconfig, I'm in favor of removing draft status and merging. I can send a separate PR for updating the patch from nixpkgs.

(also, early testing indicates this "just works" with rpi02!)

[samueldr]

Any particular reason for this still being a draft?

[leo60228]

Oh, good point.

[samueldr]

I'll test this at least in the cycle for -004, but given @colemickens' recent attempts, it seems like it's going to be an easy replacement.

[leo60228]

Merge conflicts fixed. (note to self: test this more thoroughly, you have a Pi 3B+, 4B, and Zero 2 W...)