[U-Boot] Merging device trees at runtime for module-based systems

[Mitch Bradley]

On 10/31/2012 6:36 PM, Stephen Warren wrote:
> On 10/31/2012 05:56 PM, Mitch Bradley wrote:
>> On 10/31/2012 1:00 PM, Daniel Mack wrote:
>>> cc devicetree-discuss. Here's a reference to the full thread:
>>>
>>>   http://thread.gmane.org/gmane.comp.boot-loaders.u-boot/145221/
>>>
>>> On 26.10.2012 20:39, Stephen Warren wrote:
>>>> On 10/24/2012 03:47 AM, Daniel Mack wrote:
>>>>> Hi,
>>>>>
>>>>> a project I'm involved in uses a module/baseboard combo, and components
>>>>> on either board are described in DT. I'm currently using separate dts
>>>>> files which build upon each other with include statements, which works
>>>>> fine for development.
>>>>>
>>>>> In production though, we will certainly have running changes (and hence
>>>>> different versions) over the lifetime of the product for both the
>>>>> baseboard and the module, and the hardware has support for identifying
>>>>> the versions of both sides at runtime.
> ...
>>> I start to believe that the cleanest solution to this would be to
>>> have full DTC functionality in U-Boot and compile the tree
>>
>> ... which is exactly the way that Open Firmware does it, since the
>> invention of the device tree.  The model is that the boot firmware,
>> which needs to know the system configuration to do its job anyway,
>> exports that configuration via the device tree.
> 
> Doesn't OF generate the DT from internal data structures (although I
> don't know where those come from...), whereas what Daniel mentions above
> is more like the bootloader having access to a bunch of .dts fragments,
> selecting the appropriate subset of those to use, parsing them into an
> internal data structure (i.e. running dtc), and then generating a DTB
> from it. The overall result is that the bootloader causes a DTB to be
> generated at run-time, so at that level it's the same, but the
> implementation seems pretty different.

Yes, which is why I cut the cited sentence at the place I did (before
the part about dts fragments).

>