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From:   Jonas Gorski <jonas.gorski@gmail.com>
Date:   Thu, 21 Feb 2019 22:13:55 +0100
Message-ID: <CAOiHx=k--4gOnERK4qJ6QfMyqqeAn4CQfYFeBZYRieWAa19cDw@mail.gmail.com>
Subject: Re: [PATCH] MIPS: ingenic: Add support for appended devicetree
To:     Paul Cercueil <paul@crapouillou.net>
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>,
        James Hogan <jhogan@kernel.org>, linux-mips@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Thu, 21 Feb 2019 at 21:39, Paul Cercueil <paul@crapouillou.net> wrote:
>
> Add support for booting the kernel from an externally-appended
> devicetree, if no devicetree was built-in.
>
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> ---
>  arch/mips/Kconfig        |  2 +-
>  arch/mips/jz4740/setup.c | 14 +++++++++++---
>  2 files changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index a84c24d894aa..8b7ea9062198 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -391,7 +391,7 @@ config MACH_INGENIC
>         select GPIOLIB
>         select COMMON_CLK
>         select GENERIC_IRQ_CHIP
> -       select BUILTIN_DTB
> +       select BUILTIN_DTB if MIPS_NO_APPENDED_DTB
>         select USE_OF
>         select LIBFDT
>
> diff --git a/arch/mips/jz4740/setup.c b/arch/mips/jz4740/setup.c
> index afb40f8bce96..5c00064937c4 100644
> --- a/arch/mips/jz4740/setup.c
> +++ b/arch/mips/jz4740/setup.c
> @@ -31,6 +31,7 @@
>
>  #define JZ4740_EMC_SDRAM_CTRL 0x80
>
> +extern const char __appended_dtb;

Does this build/link with MIPS_NO_APPENDED_DTB? I would assume it
won't be able to resolve the symbol in that case.

You can also just use fw_passed_dtb from asm/bootinfo.h, which will be
populated automatically from fw_args (if UHI) or __appended_dtb (if
present and valid)[1], without having to care where it came from.

Regards
Jonas

[1] https://elixir.bootlin.com/linux/latest/source/arch/mips/kernel/head.S#L96