About Beaglebone Black device tree

[Christian Mauderer]

On 31/01/2020 16:04, Vijay Kumar Banerjee wrote:
> Hi,
> 
> While trying to run an rtems-littlevgl app on BBB, I found that the device
> tree generated from the freebsd source matching the freebsd-org
> HEAD commit doesn't work with the app and framebuffer device fails
> to open. This is most likely due to the changes in the freebsd dts
> sources because of which the overlay isn't working as expected.

If I remember correctly, SD card doesn't work either with a FDT that is
too new.

> 
> I haven't had a detailed look at what's missing and the u-boot isn't
> reporting any error in applying the overlay either. I checked that the
> device tree built from freebsd tree matching the following commit
> works:
> 19a6ceb89dbacf74697d493e48c388767126d418

At the moment that's the right one. But that can change if someone
updates libbsd again.

> 
> This brings up two questions:
> 1. Should we add the commit hash in the user manual so that the user can
> build
>     from source matching that commits instead of HEAD. This can be a
> problem 
>     as other codes ported from freebsd might break if the device tree
> doesn't
>     match the HEAD commit of freebsd-org

Adding a fixed commit id isn't really a good idea either. It is nearly
guaranteed that no one updates it if libbsd is updated. It would be
better to add instructions how to find out which commit should be used.

> 
> 2. How do we manage the device tree overlays required by RTEMS or libbsd?
>     I guess only BBB uses an overlay currently. Can we add a BSD license to
>     the overlay and add it somewhere in rtems or rtems-libbsd repository and
>     maintain it?

I think you wrote the overlay so you can add any license you want. But
I'm really not sure where to put it. We currently don't have a location
for that. Do you have a good suggestion?

Best regards

Christian

> 
> Best regards,
> Vijay>
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