Re: Move device tree generation from include file to bbclass

Bach, Pascal <pascal.bach@...>

Hi Bruce, Hi Nikolay

Adding oe-core, since that's the right place to have a discussion
like this.
Thanks I'm never sure where to ask what :)

As ARM now also moved to device tree it look like in future we
have more kernels that are using device tree then ones that are

True, but it has been like this for quite some time now :)

As far as I understand currently the generation of device trees is
controlled via KERNEL_DEVICETREE and is handled in via an include
file recipes-kernel/linux/

I was thinking about moving this include into a class so it
easier to use. Before I dive into implementing something I would
like some feedback from the community.

The big trick with changing anything like this is compatibility
existing recipes. Whatever we do, existing recipes and layers
shouldn't be broken .. or if they are broken, there should be a
compelling technical reason to do so.

I have the following variant in mind.

Add the device tree generation to the current kernel.bbclass (or
let kernel.bblcass inherit from a kernel-dtb.bbclass).
This way all kernels would automatically be DT enabled. The class
would check if KERNEL_DEVICETREE is set and generate device trees
based on this information. For boards that don't have
KERNEL_DEVICETREE set the class would do nothing and the behavior
is like before. The advantage I see with this approach is that the
only thing a user needs to do is to set KERNEL_DEVICETREE in the
board and make sure the device trees are available in the kernel
they like to build.

That's pretty much the experience that most users have now, since
there's nearly always a kernel recipe created, that recipe includes, and sets KERNEL_DEVICETREE.

As far as I understood, Pascal's idea is to remove the need for user
recipes to include, and provide this functionality via
That is obvious. My questions are around "why". There's no big
technical advantage, and if you remove that existing file, you break
existing recipes. Which means you need to leave a stub in place.

So without a technical advantage, it's churn for the sake of churn.
Well, removing redundancy and simplifying users' recipes could be
considered an advantage. Also, as the contents of are
going to be moved to bbclass, the file can be left empty, later
maintainers remove the extra line from all users' recipes in following
commits. I don't see breaking as an option.
I completely agree that it is not worth to breaking existing recipes because of that.
But I think the option with an empty is acceptable.

Everything else happens to build and package the device tree.

Was there something specifically that was causing issues with the
current way of building them ?
There was no specific issue except that it feels like an unnecessary includes.
And it seems a bit odd to me that most of the work of building the kernel is done in bbclasses,
while just the dtb handling is done with an include. But of course it still is more of a cosmetic
change than a real technical necessity.


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