I don't know what you're talking about. If the device boots, you find the device tree in /sys/firmware/fdt, or in unpacked human-readable form in /sys/firmware/devicetree/* .
And you're stuck with whatever fucked up kernel the vendor gave you, assuming they even followed their obligations and gave you access to the source. The vast majority of x86 systems run mainline kernels because there's a sufficient level of abstraction. The number of Arm devices that's true for is a tiny percentage of the Arm devices out there running Linux.
