About Beaglebone Black device tree

[Christian Mauderer]

On 02/02/2020 18:34, Vijay Kumar Banerjee wrote:
> 
> 
> 
> On Sun, Feb 2, 2020 at 9:49 PM Christian Mauderer <list at c-mauderer.de
> <mailto:list at c-mauderer.de>> wrote:
> 
> 
>     On 31/01/2020 17:43, Vijay Kumar Banerjee wrote:
>     >
>     >
>     > On Fri, Jan 31, 2020 at 9:59 PM Christian Mauderer
>     <list at c-mauderer.de <mailto:list at c-mauderer.de>
>     > <mailto:list at c-mauderer.de <mailto:list at c-mauderer.de>>> wrote:
>     >
>     >     On 31/01/2020 17:25, Christian Mauderer wrote:
>     >     > 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.
>     >
>     >     And I have to correct myself: That is not the right one. The
>     current
>     >     libbsd HEAD should work with
>     6b0307a0a5184339393f555d5d424190d8a8277a.
>     >
>     > I meant to say that the framebuffer doesn't work with the current HEAD
>     > (6b0307).
>     > I checked with a previous commit, which is 19a6ce and found it
>     working.
>     > I should have been clear in the problem statement, sorry about that.
> 
>     Thats not good. But the correct way would be to find out what's wrong
>     and fix it. Did they add a fix in a future FreeBSD version?
> 
> Most likely the overlay isn't working as expected. I'll have to have a
> detailed
> look to figure out what's going on there. 
> 
>     >
>     >     >
>     >     >>
>     >     >> 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.
>     >
>     >     The command would be:
>     >
>     >         git ls-files -s freebsd-org
>     >
>     >     It works regardless whether the sub-module is initialized or not.
>     >
>     >     >
>     >     >>
>     >     >> 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?
>     >     >
>     >
>     > How about rtemsbsd/sys/dts/arm/overlays ?
>     > Following the freebsd tree freebsd/sys/dts/arm/overlays/
> 
>     Following the FreeBSD tree is a good point. But would they be visible
>     there? Beneath that: We currently don't have support for building the
>     overlays. Do you have an idea how that could look like?
> 
> keeping it visible will be a problem. For building the overlay, we can
> use dtc
> and add a script to build the overlay. I see that rsb has a build
> package for
> devel/dtc.bset as well. 

Hm. Optimal would be an integration into waf. Something like "waf
fdt-overlay". Even better would be if we could build the original fdt
too. But I'm sure that both would be quite a bit tricky to integrate
(the waf scripts in libbsd are not really easy to understand). So I'm
not insisting on that.

> 
>     Best regards
> 
>     Christian
> 
>     >
>     >     > Best regards
>     >     >
>     >     > Christian
>     >     >
>     >     >>
>     >     >> Best regards,
>     >     >> Vijay>
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>     >     >>
>     >
> 
> 
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