OF_UPSTREAM vs. additional dtbs

[Jan Kiszka]

On 26.08.24 09:10, Sumit Garg wrote:
> On Mon, 26 Aug 2024 at 12:19, Jan Kiszka <jan.kiszka at siemens.com> wrote:
>>
>> On 26.08.24 08:44, Sumit Garg wrote:
>>> Hi,
>>>
>>> On Wed, 14 Aug 2024 at 22:14, Jan Kiszka <jan.kiszka at siemens.com> wrote:
>>>>
>>>> On 14.08.24 11:41, Jan Kiszka wrote:
>>>>> On 13.08.24 14:52, Nishanth Menon wrote:
>>>>>> On 11:16-20240813, Jan Kiszka wrote:
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I'm trying to migrate the TI AM65x IOT2050 boards to OF_UPSTREAM but I'm
>>>>>>> facing issues because I need to still build the u-boot-only overlays. It
>>>>>>> is also a bit weird (but works) having to specify
>>>>>>>
>>>>>>> CONFIG_SPL_OF_LIST="../../../../arch/arm/dts/k3-am65-iot2050-spl"
>>>>>>>
>>>>>
>>>>> Actually, this does NOT work: I just had a long morning debugging SPL
>>>>> which no longer started because it picked the non-filtered dtb. The
>>>>> filtered one ended up in a folder outside of the u-boot sources because
>>>>> of all those ../ and hard-wiring to dts/upstream.
>>>>>
>>>>>>> for our spl dtb.
>>>>>>>
>>>>>>> Are there means to still build certain dtb[o] files in arch/<arch>/dts?
>>>>>>> I'm a bit lost in the Makefile forest.
>>>>>>>
>>>>>>
>>>>>> Sumit: Any suggestions?
>>>>>>
>>>
>>> Apologies for the delayed reply. I was a bit busy with other high
>>> priority stuff.
>>>
>>>>>
>>>>> I would really like to hear some better proposals than my local
>>>>> workarounds to far. They don't converge although I already patched some
>>>>> core Makefile (overlays are building now).
>>>>>
>>>>
>>>> OK, I side-stepped the spl issue by using one of our variant DTBs for
>>>> spl as well - happens to work.
>>>
>>> That's good to know.
>>>
>>>>
>>>> For the overlays, I need to add
>>>>
>>>> --- a/scripts/Makefile.dts
>>>> +++ b/scripts/Makefile.dts
>>>> @@ -1,5 +1,7 @@
>>>>  # SPDX-License-Identifier: GPL-2.0+
>>>>
>>>> +include $(srctree)/config.mk
>>>> +
>>>>  dtb-y += $(patsubst %,%.dtb,$(subst ",,$(CONFIG_DEFAULT_DEVICE_TREE) $(CONFIG_OF_LIST) $(CONFIG_SPL_OF_LIST)))
>>>>
>>>>  ifeq ($(CONFIG_OF_UPSTREAM_BUILD_VENDOR),y)
>>>>
>>>>
>>>> in order to then be able to do
>>>>
>>>> --- a/board/siemens/iot2050/config.mk
>>>> +++ b/board/siemens/iot2050/config.mk
>>>> @@ -5,4 +5,12 @@
>>>>  # Authors:
>>>>  #   Jan Kiszka <jan.kiszka at siemens.com>
>>>>
>>>> +ifneq ($(CONFIG_SPL_BUILD),y)
>>>> +dtbo-list = \
>>>> +       k3-am6548-iot2050-advanced-m2-bkey-usb3-overlay \
>>>> +       k3-am6548-iot2050-advanced-m2-bkey-ekey-pcie-overlay
>>>> +
>>>> +dtb-y += $(patsubst %,../../../../arch/arm/dts/%.dtbo,$(dtbo-list))
>>>> +endif
>>>> +
>>>>  flash.bin: all
>>>>
>>>>
>>>> Does that make sense?
>>>
>>> A switch to OF_UPSTREAM means that we build all the DT artifacts from
>>> dts/upstream/src/ directory with the only exception that we include
>>> U-Boot specific overrides via *-u-boot.dtsi from arch/<arch>/dts. In
>>> case of overlays, is there any reason for IOT2050 board overlays not
>>> being pushed into Linux kernel repo? AFAIU, overlays are also
>>> describing puggable hardware so they shouldn't be referred to as
>>> "u-boot-only" overlays.
>>
>> We are using the overlay to massage the DT presented to the OS based on
>> firmware configuration.
> 
> Agree and more than that I prefer the firmware to own the overall DT
> and present that to the OS.
> 
>> So, those two belong to the firmware logically,
>> but - with some disclaimers, we could also try to upstream them.
> 
> For historical reasons, Linux kernel source tree has become the
> defacto upstream repo for DT sources. So it's better to contribute
> there and sync back in U-Boot.

Will do ASAP, hope to hit at least 6.12 then.

Still, this will delay our next patches for U-Boot by many months. Also
for that reason, a plan B for U-Boot local DTs should remain, no
left-or-right policy.

Jan

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