linux-kernel - Re: [PATCH] microblaze: use the common infrastructure to support built-in DTB

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Message-ID: <CAK7LNASKooM0_LuPhB0c6AfUsEB0b1Q_mo0TQvuCO2BZqYJBsQ@mail.gmail.com>
Date: Sat, 9 Nov 2024 02:27:40 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Michal Simek <monstr@...str.eu>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] microblaze: use the common infrastructure to support
 built-in DTB

On Fri, Nov 8, 2024 at 8:54 PM Michal Simek <monstr@...str.eu> wrote:
>
>
>
> On 9/18/24 06:52, Masahiro Yamada wrote:
> > MicroBlaze is the only architecture that supports a built-in DTB in
> > its own way.
> >
> > Other architectures (e.g., ARC, NIOS2, RISC-V, etc.) use the common
> > infrastructure introduced by commit aab94339cd85 ("of: Add support for
> > linking device tree blobs into vmlinux").
> >
> > This commit migrates MicroBlaze to this common infrastructure.
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
> > ---
> >
> > I do not know why MicroBlaze still adopts its own way.
> > Perhaps, because MicroBlaze supports the built-in DTB
> > before aab94339cd85 and nobody attempted migration.
> > Anyway, I only compile-tested this patch.
> > I hope the maintainer can do boot-testing.
>
> I took a look at it and it is changing current behavior.
> If you look at linux.bin and there is no DT inside. But when you patch is
> applied linux.bin contains system.dtb inside which is regression.
> Or is it intention of this patch?


I do not understand your comment.

If you look at the code in arch/microblaze/Makefile,
DTB is empty unless you build simpleImage.%


My patch still keeps obj-y within the
ifneq ($(DTB),) ... endif  block.


ifneq ($(DTB),)
obj-y += system.dtb.o
  [ snip ]
endif


So, when you build linux.bin, system.dtb is not embedded in vmlinux,
is it?



> I think there was any documentation about it's usage in past but never really
> described in upstream kernel.
> But idea was that linux.bin requires DT to be passed from bootloader via R7 reg
> but simpleImage.X is linux.bin+DTB inside and can be used without bootloader.

With my patch applied, it should still work like this.


-- 
Best Regards
Masahiro Yamada