[PATCH 2/3] dts: Add ability to build DTOs only from arch/$(ARCH)/dts

[Marek Vasut]

On 9/30/24 8:02 AM, Sumit Garg wrote:
> + Jan
> 
> Hi Marek,

Hi,

> On Sat, 28 Sept 2024 at 03:20, Marek Vasut <marex at denx.de> wrote:
>>
>> Currently the enablement of OF_UPSTREAM results on the build system
>> searching for DTs only in dts/upstream/ . There are platforms which
>> use U-Boot specific DTBOs applied on top of U-Boot control DT during
>> SPL stage, and source DTs for these are located in arch/$(ARCH)/dtb.
> 
> I would like to understand the need to maintain DTBOs separately from
> DTBs. Why aren't we pushing DTBOs to Linux kernel sources as we do for
> DTBs?

This is a stopgap measure, I would like to start reducing the amount of 
U-Boot DTs for iMX platforms, but the DTBOs are still in U-Boot only, so 
I would like to have some middle-of-the-road solution until the DTOs get 
upstreamed to Linux too.

> Jan recently pushed those so-called U-Boot specific DTBOs for a
> TI platform which were accepted in the Linux kernel upstream. This
> patch will just deny the ability to build those DTBOs from dts
> upstream tree. IMHO, this takes a step backwards on the whole notion
> of OF_UPSTREAM.

I don't think this will deny building those DTOs which are already 
upstream. With OF_UPSTREAM enabled, this will build:
- Upstream DTBs
- Upstream DTBOs
- U-Boot local DTBOs (and NOT U-Boot local DTBs)
The DTs that are bundled into u-boot.itb are searched exactly in that 
order too, upstream ones first, upstream DTBOs second and finally the 
U-Boot local DTBOs. The upstream content should always get higher 
priority if there are any leftover DTBOs in U-Boot which are also upstream.

> If we really want a middle ground solution to allow migration to
> OF_UPSTREAM easier then we need to find a way to build DTBOs from both
> directories (local and upstream dts). I would imagine that will likely
> complicate building and packaging DTBOs.

I believe this is exactly what this commit does ?