[yocto] Move device tree generation from include file to bbclass

[Nikolay Dimitrov]

Hi Bruce,

On 04/15/2015 04:13 PM, Bruce Ashfield wrote:
> On 2015-04-15 08:33 AM, Bach, Pascal wrote:
>> Hi
>>
>
> Adding oe-core, since that's the right place to have a discussion
> like this.
>
>> As ARM now also moved to device tree it look like in future we will
>>  have more kernels that are using device tree then ones that are
>> not.
>
> 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/linux-dtb.inc.
>>
>> I was thinking about moving this include into a class so it becomes
>>  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 with
> 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
> linux-dtb.inc, and sets KERNEL_DEVICETREE.

As far as I understood, Pascal's idea is to remove the need for user
recipes to include linux-dtb.inc, and provide this functionality via
inheritance.

> 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 ?
>
> Cheers,
>
> Bruce
>
>>
>> I appreciate your feedback?
>>
>> Regards Pascal
>>
>

Regards,
Nikolay