Re: Call for Testing: Switching back to our BSD licensed dtc(1)

On 23 Jul 2016, at 05:16, Warner Losh <imp_at_bsdimp.com> wrote:
> 
> On Fri, Jul 22, 2016 at 1:03 AM, David Chisnall <theraven_at_freebsd.org> wrote:
>> On 22 Jul 2016, at 03:40, Warner Losh <imp_at_bsdimp.com> wrote:
>>> 
>>> On Wed, Jul 20, 2016 at 9:51 AM, David Chisnall <theraven_at_freebsd.org> wrote:
>>>> On 20 Jul 2016, at 16:46, Warner Losh <imp_at_bsdimp.com> wrote:
>>>>> 
>>>>> I've been trying to get the final spec for it. Right now it's a
>>>>> disorganized series
>>>>> of patches, some of which have been merge some that haven't. I'll send you a
>>>>> copy when I can find something better than "here's the code."
>>>> 
>>>> Thanks.  From the information I can find, it looks as if most of the machinery required to implement it is already in dtc, so it should (hopefully) just be a matter of adding a new keyword to detect plugins, a scan to find the cross-references (or possibly reusing the existing one) and then a little bit of extra logic.
>>> 
>>> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/overlay-notes.txt
>>> has the specs.
>> 
>> Hmm, that’s even less complete than the docs that I’d found.
> 
> Can you share that then?

I only found tutorial-style things:

https://www.raspberrypi.org/documentation/configuration/device-tree.md

https://learn.adafruit.com/introduction-to-the-beaglebone-black-device-tree/device-tree-overlays

I was hoping for something a bit more like a spec.


>> From that, it seems as if the only thing that dtc needs to do is support the /plugin/ syntax and emit a section describing unresolved references?
> 
> I believe so, yes.

That sounds like it should be easy.

> 
>> Or is dtc also expected to be able to do the merging?
> 
> I think that's TBD. We'll need, at the very least, an update libfdt
> from upstream that knows how to do the merging, as well as changes to
> /boot/loader to be able to pick and choose which plugins to add to the
> base. If we can do all that with the BSDL DTC and it passes all the
> other GPL test cases, then we may have a winner and we can get started
> integrating plugin support to /boot/loader. I know my RPi would be
> happier if it had a 'standard' DTB with a plugin for whatever 1-wire
> stuff I'm playing with today.

Patrick Wildt was running the GPL’d dtc test suite and I fixed all of the things that he reported broken.  We’re now using a less-efficient algorithm for calculating the cross-references so that we resolve things in the same order, which makes doing a diff on the dts produced by the two tools easier.

David