linux-kernel - Re: [PATCH 05/11] vmlinux.lds.h: Preserve DTB sections from being discarded after init

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Message-ID: <CAK7LNAQ1oUvuMcHs-idZcPxE-c4fJgMDt-cURATsrVkjjFPNWg@mail.gmail.com>
Date: Tue, 24 Sep 2024 11:45:58 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: Stephen Boyd <sboyd@...nel.org>
Cc: Andrea della Porta <andrea.porta@...e.com>, Andrew Lunn <andrew@...n.ch>, Arnd Bergmann <arnd@...db.de>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, 
	Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, 
	Catalin Marinas <catalin.marinas@....com>, Claudiu Beznea <claudiu.beznea@...on.dev>, 
	Conor Dooley <conor+dt@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
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	Eric Dumazet <edumazet@...gle.com>, Florian Fainelli <florian.fainelli@...adcom.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jakub Kicinski <kuba@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Lee Jones <lee@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Michael Turquette <mturquette@...libre.com>, 
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	Will Deacon <will@...nel.org>, devicetree@...r.kernel.org, linux-arch@...r.kernel.org, 
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Subject: Re: [PATCH 05/11] vmlinux.lds.h: Preserve DTB sections from being
 discarded after init

On Tue, Sep 24, 2024 at 3:13 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Masahiro Yamada (2024-09-22 01:14:12)
> >
> > Rather, I'd modify my patch as follows:
> >
> > --- a/scripts/Makefile.dtbs
> > +++ b/scripts/Makefile.dtbs
> > @@ -34,12 +34,14 @@ $(obj)/dtbs-list: $(dtb-y) FORCE
> >  # Assembly file to wrap dtb(o)
> >  # ---------------------------------------------------------------------------
> >
> > +builtin-dtb-section = $(if $(filter arch/%, $(obj)),.dtb.init.rodata,.rodata)
>
> I think we want to free the empty root dtb that's always builtin. That
> is in drivers/of/ right?


drivers/of/empty_root.dts is really small.

That is not a big deal even if empty_root.dtb
remains in the .rodata section.



> And I worry that an overlay could be in arch/
> and then this breaks again. That's why it feels more correct to treat
> dtbo.o vs. dtb.o differently. Perhaps we can check $(obj) for dtbo vs
> dtb?


This is not a problem either.


Checking $(obj)/ is temporary.

See this later patch:

https://lore.kernel.org/linux-kbuild/20240904234803.698424-16-masahiroy@kernel.org/T/#u

After my work is completed, DTB and DTBO will go
to the .rodata section unconditionally.



> Also, modpost code looks for .init* named sections and treats them as
> initdata already. Can we rename .dtb.init.rodata to .init.dtb.rodata so
> that modpost can find that?


My previous patch checked .dtb.init.rodata.

I do not mind renaming it to .init.dtb.rodata.







-- 
Best Regards
Masahiro Yamada