[OE-core] How to set up custom layer correctly

[Ankur Tyagi]

Hi,

I have a custom layer for custom board based upon am335x-evm and custom images.

I have a master layer called "my-custom-layer" which has three sub-layers
- my-custom-distro : custom distro based upon TI's 'arago' distro, Qt
and other s/w recipe appends
- my-custom-image : custom images, packagegroups, toolchain recipes
- my-custom-machine : custom machine conf, bsp and kernel recipes

When I am building my image, it throws numerous warnings like below
for almost all packages in the image:

eudev-3.2.7-r0.3.arago5 do_package_qa: QA Issue: libudev rdepends on
u-boot-custom-src, but it isn't a build dependency, missing
u-boot-custom in DEPENDS or PACKAGECONFIG? [build-deps]
WARNING: eudev-3.2.7-r0.3.arago5 do_package_qa: QA Issue: eudev
rdepends on u-boot-custom-src, but it isn't a build dependency,
missing u-boot-custom in DEPENDS or PACKAGECONFIG? [build-deps]
WARNING: libinput-1.11.3-r0 do_package_qa: QA Issue: libinput rdepends
on u-boot-custom-src, but it isn't a build dependency, missing
u-boot-custom in DEPENDS or PACKAGECONFIG? [build-deps]
WARNING: libinput-1.11.3-r0 do_package_qa: QA Issue: libinput-bin
rdepends on u-boot-custom-src, but it isn't a build dependency,
missing u-boot-custom in DEPENDS or PACKAGECONFIG? [build-deps]


And once sstate-cache is built and if I try to reuse it after bumping
u-boot-custom to new SRCREV then I get errors like:

Collected errors:
 * Solver encountered 2 problem(s):
 * Problem 1/2:
 *   - nothing provides u-boot-custom-src >= 2019.01+git0+b31ea1d606
needed by linux-custom-src-4.19.73+git0+d02acfec3d-gamos.wsl
 *
 * Solution 1:
 *   - do not ask to install a package providing packagegroup-ggl-base

 * Problem 2/2:
 *   - nothing provides u-boot-custom-src >= 2019.01+git0+b31ea1d606
needed by linux-custom-src-4.19.73+git0+d02acfec3d-gamos.wsl
 *
 * Solution 1:
 *   - do not ask to install a package providing packagegroup-ggl-qt

Something is definitely not right the way I am have setup my layers
but I would like to understand what is wrong, why it is wrong and what
is the recommended way to do it
Because in future I would like to add different machines, distros and
images for different custom products. That is why instead of putting
everything inside one layer I thought of keeping a separate layer for
each.

Looking forward to learning from your responses.

Thanks
Ankur