Re: [PATCH] ARM: head.S: explicitly map DT even if it lives in the first physical section

[Linus Walleij <linus.walleij@linaro.org>]

On Mon, Nov 16, 2020 at 3:57 PM Ard Biesheuvel <ardb@kernel.org> wrote:

> The early ATAGS/DT mapping code uses SECTION_SHIFT to mask low order
> bits of R2, and decides that no ATAGS/DTB were provided if the resulting
> value is 0x0.
>
> This means that on systems where DRAM starts at 0x0 (such as Raspberry
> Pi), no explicit mapping of the DT will be created if R2 points into the
> first 1 MB section of memory. This was not a problem before, because the
> decompressed kernel is loaded at the base of DRAM and mapped using
> sections as well, and so as long as the DT is referenced via a virtual
> address that uses the same translation (the linear map, in this case),
> things work fine.
>
> However, commit 149a3ffe62b9dbc3 ("9012/1: move device tree mapping out of
> linear region") changes this, and now the DT is referenced via a virtual
> address that is disjoint from the linear mapping of DRAM, and so we need
> the early code to create the DT mapping unconditionally.
>
> So let's create the early DT mapping for any value of R2 != 0x0.
>
> Fixes: 149a3ffe62b9dbc3 ("9012/1: move device tree mapping out of linear region")
> Reported-by: Guillaume Tucker <guillaume.tucker@collabora.com>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

That's a good catch!
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij

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