External dts building

[Simon Glass]

Hi Giulio,

On Thu, 14 Oct 2021 at 21:06, Giulio Benetti
<giulio.benetti at benettiengineering.com> wrote:
>
> Hi Simon,
>
> > Il giorno 15 ott 2021, alle ore 02:53, Simon Glass <sjg at chromium.org> ha scritto:
> >
> > Hi Giulio,
> >
> >> On Thu, 14 Oct 2021 at 15:12, Giulio Benetti
> >> <giulio.benetti at benettiengineering.com> wrote:
> >>
> >> Hi Simon,
> >>
> >> Il giorno 14 ott 2021, alle ore 22:43, Simon Glass <sjg at chromium.org> ha scritto:
> >>
> >> Hi Giulio,
> >>
> >> On Thu, 14 Oct 2021 at 13:23, Giulio Benetti
> >> <giulio.benetti at benettiengineering.com> wrote:
> >>
> >>
> >> Hi Simon,
> >>
> >>
> >> Il giorno 14 ott 2021, alle ore 20:24, Simon Glass <sjg at chromium.org> ha scritto:
> >>
> >>
> >> Hi,
> >>
> >>
> >> On Thu, 14 Oct 2021 at 07:46, Tom Rini <trini at konsulko.com> wrote:
> >>
> >>
> >> On Thu, Oct 14, 2021 at 02:53:30AM +0200, Giulio Benetti wrote:
> >>
> >>
> >> Hello All,
> >>
> >>
> >> is there a way to pass a dts file without touching the arch/arm/boot/dts/Makefile?
> >>
> >>
> >> On Buildroot we support the possibility to pass an external dts by copying it to the uboot sources to
> >>
> >> be built but since uboot version 2020.01 it doesn’t work anymore.
> >>
> >>
> >> So I’ve proposed a patch to prepend the dts file in the Makefile above, but this has drawbacks, like we reconfigure(it keeps adding files every time).
> >>
> >>
> >> So I ask you, is there a more canonical way already to achieve this?
> >>
> >>
> >> Not exactly, and it's something we're very much actively discussing
> >>
> >> right now.
> >>
> >>
> >> Are you using 'make DEVICE_TREE=xxx' ?
> >>
> >>
> >> Yes but it doesn’t work if you don’t add an entry into arch/arm/dts/Makefile
> >>
> >> Before version 2020.01 worked, but not after it.
> >>
> >>
> >> What board are you building?
> >>
> >>
> >> A20-OLinuXino-Lime_defconfig for but without CONFIG_DEFAULT_DEVICE_TREE undefined,
> >> so if you try to pass DEVICE_TREE= pointing to an external .dts file copied to arch/arm/dts/ make doesn’t find the entry in Makefile and it can’t build it.
> >>
> >> This is useful in build systems like Buildroot where you can provide an external defconfig as well as an external .dts file.
> >>
> >> So here the solution I see is to create an entry in arch/arm/dts/Makefile on the top of the file afte copying the .dts file we want to build.
> >> But on Buildroot they’ve pointed me to ask upstream(here) if there’s a more canonical way or to work together to achieve the goal:
> >>
> >> https://patchwork.ozlabs.org/project/buildroot/patch/20210209201303.195093-1-giulio.benetti@benettiengineering.com/
> >
> > How about not disabling CONFIG_DEFAULT_DEVICE_TREE ? That should work OK.
>
> But if I’m not wrong the problem of the dts/Makefile remains. If .dts file is not assigned to dtb-y it won’t be built.
>
> And in the case of Buildroot we have 2 ways to use external dts files:
> 1) patch uboot adding the dts and the entry in dts/Makefile
> 2) copy .dts file(let’s say located in ~/my-folder/my.dts) to arch/arm/dts/my.dts and prepend
> the dtb-y += my.dts in arch/arm/dts/Makefile and here problem arises.
> Because it can work once but we need to make it possible to have ‘make uboot-rebuild/reconfigure’
> (Buildroot has such targets). This way is not easy at all to prepend the dtb-y at the top of the file without re-prepending it again and again.
>
> It worked up to uboot < 2020.01, but I still haven’t bisected to see the “offending” commit.
> Maybe I can try and find out why it behaves like that.
>
> What about that?

Have you tried EXT_DTB? It looks like DEVICE_TREE is designed for
changing the name of the file.

EXT_DTB=/tmp/b/sandbox/u-boot.dtb
CROSS_COMPILE=/home/sglass/.buildman-toolchains/gcc-9.2.0-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-
make O=/tmp/b/snow -j30 snow_defconfig all

You need to compile it first though.

For your case, I did a bisect with:

git bisect run make -s DEVICE_TREE=try
CROSS_COMPILE=/home/sglass/.buildman-toolchains/gcc-9.2.0-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-
O=/tmp/b/snow -j30 mrproper snow_defconfig all

and got:

a3444bd09af (refs/bisect/bad) Revert "Ensure device tree DTS is compiled"

+Masahiro Yamada who might know

BTW if you rely on this feature, once it is working again, we should
add a test for it.

Regards,
Simon