[PATCH] mm: use correct section size macro to describe the FDT virtual address

[Linus Walleij]

On Wed, Oct 28, 2020 at 2:25 PM Ard Biesheuvel <ardb at kernel.org> wrote:

>   149a3ffe62b9dbc3 ("9012/1: move device tree mapping out of linear region")
>
> created a permanent, read-only section mapping of the device tree blob
> provided by the firmware, and added a set of macros to get the base and
> size of the virtually mapped FDT based on the physical address. However,
> while the mapping code uses the SECTION_SIZE macro correctly, the macros
> use PMD_SIZE instead, which means something entirely different on ARM when
> using short descriptors, and is therefore not the right quantity to use
> here. So replace PMD_SIZE with SECTION_SIZE. While at it, change the names
> of the macro and its parameter to clarify that it returns the virtual
> address of the start of the FDT in memory, based on the physical address
> in memory.
>
> Tested-by: Joel Stanley <joel at jms.id.au>
> Tested-by: Marek Szyprowski <m.szyprowski at samsung.com>
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>

2 * SECTION_SIZE will be 2 MB on classic MMU and 4MB on
LPAE right?

Note in Documentation/arm/memory.rst:

> -ffc00000 ffefffff Fixmap mapping region.  Addresses provided
> +ffc80000 ffefffff Fixmap mapping region.  Addresses provided
>      by fix_to_virt() will be located here.
>
> +ffc00000 ffc7ffff Guard region
> +
> +ff800000 ffbfffff Permanent, fixed read-only mapping of the
> + firmware provided DT blob

So on the classic MMU the DTB mapping will use 0xff800000-0xff9fffff
and on LPAE it will use the whole 0xff800000-0xffbfffff as in the doc?

Just verifying that I understand this right...

If I have understood what I just reviewed right:
Reviewed-by: Linus Walleij <linus.walleij at linaro.org>

Yours,
Linus Walleij