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

[Bruce Ashfield]

On Wed, Apr 15, 2015 at 11:22 AM, Nikolay Dimitrov <picmaster at mail.bg> wrote:
> 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.

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.

Bruce

>
>> 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
>
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