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

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Message-ID: <2113b8df52164733a0ee3860bb793d6e.sboyd@kernel.org>
Date: Fri, 30 Aug 2024 12:46:35 -0700
From: Stephen Boyd <sboyd@...nel.org>
To: 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>, Derek Kiernan <derek.kiernan@....com>, Dragan Cvetic <dragan.cvetic@....com>, 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>, Nicolas Ferre <nicolas.ferre@...rochip.com>, Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>, Stefan Wahren <wahrenst@....net>, Will Deacon <will@...nel.o
 rg>, devicetree@...r.kernel.org, linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org, linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, linux-rpi-kernel@...ts.infradead.org, netdev@...r.kernel.org
Subject: Re: [PATCH 05/11] vmlinux.lds.h: Preserve DTB sections from being discarded after init

Quoting Andrea della Porta (2024-08-20 07:36:07)
> The special section .dtb.init.rodata contains dtb and dtbo compiled
> as objects inside the kernel and ends up in .init.data sectiion that
> will be discarded early after the init phase. This is a problem for
> builtin drivers that apply dtb overlay at runtime since this happens
> later (e.g. during bus enumeration) and also for modules that should
> be able to do it dynamically during runtime.
> Move the dtb section to .data.
> 
> Signed-off-by: Andrea della Porta <andrea.porta@...e.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index ad6afc5c4918..3ae9097774b0 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -365,6 +365,7 @@
>         TRACE_PRINTKS()                                                 \
>         BPF_RAW_TP()                                                    \
>         TRACEPOINT_STR()                                                \
> +       KERNEL_DTB()                                                    \

The KERNEL_DTB() macro shows the section name is dtb.init.rodata. Can
you remove the ".init." part if this isn't initdata anymore? And
shouldn't it be in the RO_DATA() macro?

It would be nice to keep the initdata properties when this isn't used
after init as well. Perhaps we need another macro and/or filename to
indicate that the DTB{O} can be thrown away after init/module init.