NixOS
Enabling USB on RPI CM4
When attempting to enable USB's on my PI CM4 I thought enabling xhci (through hardware.raspberry-pi."4".xhci.enable = true;) would fix it, but it in turn causes the following build error. Am I missing something or is this just not supported yet?
Processing source device tree broadcom/bcm2711-rpi-4-b.dtb...
Applying overlay enable-xhci
Applying overlay rpi4-cpu-revision
Saving final device tree broadcom/bcm2711-rpi-4-b.dtb...
Processing source device tree broadcom/bcm2711-rpi-400.dtb...
Applying overlay enable-xhci
Skipping overlay rpi4-cpu-revision: {'raspberrypi,4-model-b'} is incompatible with {'raspberrypi,400'>
Saving final device tree broadcom/bcm2711-rpi-400.dtb...
Processing source device tree broadcom/bcm2711-rpi-cm4-io.dtb...
Applying overlay enable-xhci
Traceback (most recent call last):
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 102, in <module>
main()
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 92, in main
dt = apply_overlay(dt, overlay.fdt)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 50, in apply_overlay
raise FdtException(err)
libfdt.FdtException: pylibfdt error -1: FDT_ERR_NOTFOUND
...skipping...
Processing source device tree broadcom/bcm2711-rpi-4-b.dtb...
Applying overlay enable-xhci
Applying overlay rpi4-cpu-revision
Saving final device tree broadcom/bcm2711-rpi-4-b.dtb...
Processing source device tree broadcom/bcm2711-rpi-400.dtb...
Applying overlay enable-xhci
Skipping overlay rpi4-cpu-revision: {'raspberrypi,4-model-b'} is incompatible with {'raspberrypi,400'>
Saving final device tree broadcom/bcm2711-rpi-400.dtb...
Processing source device tree broadcom/bcm2711-rpi-cm4-io.dtb...
Applying overlay enable-xhci
Traceback (most recent call last):
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 102, in <module>
main()
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 92, in main
dt = apply_overlay(dt, overlay.fdt)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/nix/store/206l37y6cvcwl3ck1ppwgnxn4cnm818i-apply_overlays.py", line 50, in apply_overlay
raise FdtException(err)
libfdt.FdtException: pylibfdt error -1: FDT_ERR_NOTFOUND
I've also tried using dwc2 in every mode possible but none of them seem to make my ports work again.
I am have come across the same issue, and it seems to be related to the GPU (added in https://github.com/NixOS/nixos-hardware/pull/261) not working on CM4 either, as discussed in https://github.com/NixOS/nixos-hardware/issues/631.
As far as I understand, this is because enabling the fkms-3d modesetting patch removes all device tree variants except those of the Pi 4B and Pi 400 since https://github.com/NixOS/nixos-hardware/pull/693 because it failed to apply the overlays to the bcm2711-rpi-cm4-io device tree variant, which is also the case for the xhci it seems. When enabling the fkms-3d patch, even though the GPU doesn't actually work, the CM4 bootloader loads the Pi 4B device tree and therefore enables USB even without the xhci.enable setting.
I am not exactly sure what the CM4-IO DT variant is used for, I cannot find any documentation about it from Raspberry Pi or anywhere else. It seems to be for the CM4 IO Board, but it removes a bunch of CPU peripherals (like GPU), so I cannot imagine it being a replacement for the regular CM4 version when running on the IO board. Does anyone else know about this?
I have gotten both the GPU and USB to work on the CM4 by enabling both the fkms-3d and xhci options and modifying this line to the following:
hardware.deviceTree.filter = "bcm2711-rpi-[4c][-0m][b04].dtb";
This allows both the 4B, 400 and CM4 variants, but still excludes the problematic CM4-IO. I seems to not cause any issues, so I don't know why it was decided against allowing the CM4 in https://github.com/NixOS/nixos-hardware/issues/631 and https://github.com/NixOS/nixos-hardware/pull/693 (except for the horrible glob syntax), but maybe I am missing something or something has changed since then. I am testing this using 25.05.
Also I don't quite understand which device trees we are modifying here, as the the ones included on the firmware partition (presumably loaded by the bootloader?) are copied directly from the upstream raspberry pi firmware repository, where the cm4-io variant isn't even included... so when and by what component are these modified device trees loaded?
I've also tried using dwc2 in every mode possible but none of them seem to make my ports work again.
As a workaround, I found this to work on a couple devices as long as otg_mode is not set in the firmware config.txt file.
{
hardware.raspberry-pi."4".dwc2 = {
enable = true;
dr_mode = "host";
};
}
