Re: [PATCH 4/4] microblaze: remove unnecessary system.dts

[Masahiro Yamada <masahiroy@kernel.org>]

On Sat, Feb 1, 2025 at 7:25 AM Rob Herring <robh@kernel.org> wrote:
>
> On Tue, Jan 14, 2025 at 12:15 PM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > The default image linux.bin does not contain any DTB, but a separate
> > system.dtb is compiled.
> >
> > Michal Simek clearly explained "system.dtb is really old dtb more for
> > demonstration purpose and nothing else and likely it is not working on
> > any existing board." [1]
> >
> > The system.dts is not necessary even for demonstration purposes. There
> > is no need to compile out-of-tree *.dts under arch/microblaze/boot/dts/
> > unless it is embedded into the kernel. Users can directly use dtc.
> >
> > [1]: https://lore.kernel.org/all/d2bdfbfd-3721-407f-991e-566d48392add@amd.com/
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> >  arch/microblaze/boot/dts/Makefile   |   3 +-
> >  arch/microblaze/boot/dts/system.dts | 353 ----------------------------
> >  2 files changed, 1 insertion(+), 355 deletions(-)
> >  delete mode 100644 arch/microblaze/boot/dts/system.dts
> >
> > diff --git a/arch/microblaze/boot/dts/Makefile b/arch/microblaze/boot/dts/Makefile
> > index 932dc7550a1b..fa0a6c0854ca 100644
> > --- a/arch/microblaze/boot/dts/Makefile
> > +++ b/arch/microblaze/boot/dts/Makefile
> > @@ -1,8 +1,6 @@
> >  # SPDX-License-Identifier: GPL-2.0
> >  #
> >
> > -dtb-y := system.dtb
> > -
> >  ifneq ($(DTB),)
> >  obj-y += linked_dtb.o
> >
> > @@ -11,6 +9,7 @@ $(obj)/linked_dtb.o: $(obj)/system.dtb
> >
> >  # Generate system.dtb from $(DTB).dtb
> >  ifneq ($(DTB),system)
>
> Can't this be dropped as setting DTB=system.dtb should work if there's
> not an in-tree system.dts anymore.

I believe this ifneq is necessary, just in case
a user adds system.dtb to arch/microblaze/boot/dts/.

'system.dtb' is a special name because
arch/microblaze/boot/dts/linked_dtb.S wraps it.

So, $(DTB) is copied to system.dtb, and then
it is wrapped by linked_dtb.S.

If $(DTB) is already 'system',
we cannot copy system.dtb to itself.


See the definition of cmd_copy in scripts/Makefile.lib

cmd_copy = cat $< > $@


"cat system.dtb > system.dtb"
would create an empty system.dtb






>
> > +targets += system.dtb
> >  $(obj)/system.dtb: $(obj)/$(DTB).dtb FORCE
> >         $(call if_changed,copy)
> >  endif



-- 
Best Regards
Masahiro Yamada