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Date:   Thu, 16 May 2019 09:37:05 -0500
From:   Rob Herring <>
To:     Hsin-Yi Wang <>
        "" <>,
        Frank Rowand <>,
        Catalin Marinas <>,
        Will Deacon <>,
        Andrew Morton <>,
        Mike Rapoport <>,
        Ard Biesheuvel <>,
        Miles Chen <>,
        James Morse <>,
        Andrew Murray <>,
        Mark Rutland <>,
        Chintan Pandya <>,
        Jun Yao <>, Yu Zhao <>,
        Robin Murphy <>,
        Laura Abbott <>,
        Stephen Boyd <>,
        Kees Cook <>
Subject: Re: [PATCH v3 2/3] arm64: implement update_fdt_pgprot()

On Thu, May 16, 2019 at 5:28 AM Hsin-Yi Wang <> wrote:
> Basically does similar things like __fixmap_remap_fdt(). It's supposed
> to be called after fixmap_remap_fdt() is called at least once, so region
> checking can be skipped. Since it needs to know dt physical address, make
> a copy of the value of __fdt_pointer.
> Signed-off-by: Hsin-Yi Wang <>
> ---
>  arch/arm64/kernel/setup.c |  2 ++
>  arch/arm64/mm/mmu.c       | 17 +++++++++++++++++
>  2 files changed, 19 insertions(+)

Why not just map the FDT R/W at the start and change it to RO just
before calling unflatten_device_tree? Then all the FDT scanning
functions or any future fixups we need can just assume R/W. That is
essentially what Stephen suggested. However, there's no need for a
weak function as it can all be done within the arch code.

However, I'm still wondering why the FDT needs to be RO in the first place.


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