About Beaglebone Black device tree

[Christian Mauderer]

On 10/02/2020 10:24, Chris Johns wrote:
> On 2020-02-10 19:18, Christian Mauderer wrote:
>>
>> Hello Chris,
>>
>> thanks for your input. I'm still not entirely happy with the location
>> too. But I also don't know a better one. Currently I know of the
>> following necessary cases:
>>
>> - Build a dtb from FreeBSD sources (or some other source).
>>
>> - Build an overlay from some RTEMS source (for example: Using an i2c
>> adaption layer for libbsd instead of using the i2c hardware directly).
> 
> Thank you the summary. I see the issue.
> 
>> - For some targets with a simple bootloader that can only load one
>> device tree binary: Merge the overlays with the base tree.
> 
> OK. Can this be done in a tool like rtems-boot-image to merge them.
> 
>> The dts from FreeBSD could either be imported in libbsd or pulled from a
>> download (note: either many files for all dts, dtsi and headers or one
>> big file for the complete FreeBSD source tree). The overlays for RTEMS
>> are a bit less easy: There should be a place for them in RTEMS
>> somewhere. And I really don't know where would be a good one. Do you
>> have any suggestions?
> 
> It is tricky.
> 
> I suppose FDT is used to describe the hardware and we should be using it
> in RTEMS for drivers. If we locate them outside the rtems.git repo it
> will create an awkward relationship. I agree we do need to capture them
> somehow.
> 
> I am not sure what we need to do to handle these files.

Same problem here. What makes it worse is that there can be a dependency
between the libbsd version, RTEMS version and device tree files. So it's
three parts that have dependencies.

In the past discussions my approach was to document "use fdt from
FreeBSD in the same version as libbsd and use this overlay" (for example
I suggested that for last years GSoC project). But sooner or later that
won't work anymore. And it's definitively not automation friendly.

Best regards

Christian

> 
> Chris

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