OF_UPSTREAM vs. additional dtbs

[Sumit Garg]

On Mon, 26 Aug 2024 at 18:02, Jan Kiszka <jan.kiszka at siemens.com> wrote:
>
> 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.

Yeah, the U-Boot local DTs should be used until the board is fully
supported by the dts/upstream directory.

-Sumit

>
> Jan
>
> --
> Siemens AG, Technology
> Linux Expert Center
>