[yocto] Intermittent Kernel Boot Hang 4.8/Intel Z5 Atom

[Chris Trobridge]

Since switching kernel to 4.8 (Morty) I have noticed that sometimes my Intel Atom hardware (Pokini) doesn't boot Linux.

Specifically, syslinux runs fine and starts the kernel but this then hangs immediately after displaying "Booting the kernel.", producing no further output.

This is typical output, with one of my attempts to produce more output from the kernel via serial:

> /vmlinuz initrd=/initrd LABEL=boot root=/dev/ram0  video=efifb:off video=640x480 console=ttyS0,115200 verbose

Loading /vmlinuz... ok
Loading /initrd...ok

The issue seem to occur with some probability after powering the hardware but I've not seen it occur after a reboot.

4.1 and 4.4.36 are reliable and do not have any issues booting.

I've been looking through bugs/issue but not found anything relevant.  Does anyone know of issues that I might not have found that would apply?

I've also been looking at how to get more diagnostics out of the boot.  I've tried a few suggested kernel boot parameters but nothing has helped so far.   It seems to go wrong too early.  Do I need to re-build the kernel to produce more output at the early stage it fails?

Thanks,
Chris