make work on newer BBB images?

[cozzyd]

The u-boot overlay detection doesn't seem to work in updated images since the bone_capemgr stuff has all been removed, as far as I can tell. I'm not sure what the best current way to detect them is, but I think perhaps the presence of /proc/device-tree/chosen/overlays may possibly imply a u-boot overlay?

This adds a check for that when detecting device trees, making this library work on more recent images. There are probably more robust/better methods.

[RobertCNelson]

@cozzyd yeah that should be safe enough.. Ever since the cape bone_capemgr went away as of 4.5 timeframe, we've used /proc/device-tree/chosen/overlays to help show what overlay was loaded..

debian@21-am335x-bbb:~$ tree /proc/device-tree/chosen/
/proc/device-tree/chosen/
├── base_dtb
├── base_dtb_timestamp
├── bootargs
├── linux,initrd-end
├── linux,initrd-start
├── name
├── overlays
│   ├── BB-ADC-00A0.kernel
│   ├── BB-BONE-eMMC1-01-00A0.kernel
│   ├── BB-HDMI-TDA998x-00A0.kernel
│   └── name
└── stdout-path

1 directory, 11 files

and

debian@21-am335x-bbb:~$ zcat /proc/config.gz | grep CONFIG_OF_OVERLAY
CONFIG_OF_OVERLAY=y

The /proc/device-tree/chosen/overlays conscept also applies to arm64 (BeaglePlay, BBAI64), riscv64 (BeagleV-Ahead, BeagleV-Fire), and the up-coming arm64 (BeagleY-AI)..

Regards,