[yocto] [meta-raspberrypi] Basic image on all platforms

[Andrea Benini]

Hi List,
I have posted a similar question few days ago, lately I have tried more
things and permutation but my issue is still there and I'm still in the
starting point.
I'm able to compile a barebone yocto image (rpi-hwup-image.bb) for each
single RaspberryPi (1/2/3/0) board just by changing the MACHINE var. I have
removed every customization to limit possible errors but I'm not able to
produce a single image compatible with all these boards. When I set
MACHINE="raspberrypi" it works fine on RPi1 boards only and it hangs on
newer ones, during boot newer boards have a seven times flashing led
(kernel7.img missing). With MACHINE="raspberrypi2" (or "raspberrypi3) I can
see a complete boot on newer boards but it hangs on previous ones. I even
had tried some weird mix with kernel.img and kernel7.img files on the same
SD (from two different builds) to get something working but obviously after
a successful kernel boot the image complains on different loadable modules
on root partition so this shouldn't be the right path to follow.
RPi0 and RPi1 are using tune-arm1176jzf-s, RPi2 and RPi3 are
using tune-cortexa7, two different architectures for sure but with the same
base, RPi3 even has 64bit capabilities. What I'm trying to do is to adapt
my image to use the lower common specs of all these platforms, I'm aware
about the performance loss but at least I might have something compatible,
this should be possible because already raspbian did it.
Raspbian for example has kernel.img and kernel7.img files to boot on each
board

Here are my layers:
BBLAYERS ?= " \
  /home/devel/yocto/meta \
  /home/devel/yocto/meta-poky \
  /home/devel/yocto/meta-yocto-bsp \
  /home/devel/yocto/meta-openembedded/meta-oe \
  /home/devel/yocto/meta-openembedded/meta-networking \
  /home/devel/yocto/meta-openembedded/meta-python \
  /home/devel/yocto/meta-raspberrypi \
  "
I'm currently using the Morty branch, I don't know if you need more
information about the environment, just drop me a note about that.
There's probably something wrong but I'm not able to figure what it is, has
anyone ever created a cross compatible image ? I'm still experimenting so
if someone could give me a suggestion I'll try to use it.

Thanks again for your support
Ben
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