[PATCH v3 05/11] arm64/efi: adapt to relaxed FDT placement requirements

[ard.biesheuvel@linaro.org (Ard Biesheuvel)]

On 13 April 2015 at 18:35, Mark Rutland <mark.rutland@arm.com> wrote:
> On Mon, Apr 13, 2015 at 05:25:55PM +0100, Ard Biesheuvel wrote:
>> On 13 April 2015 at 18:20, Mark Rutland <mark.rutland@arm.com> wrote:
>> > On Fri, Apr 10, 2015 at 02:53:49PM +0100, Ard Biesheuvel wrote:
>> >> With the relaxed FDT placement requirements in place, we can change
>> >> the allocation strategy used by the stub to put the FDT image higher
>> >> up in memory. At the same time, reduce the minimal alignment to 8 bytes,
>> >> and impose a 2 MB size limit, as per the new requirements.
>> >>
>> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> >> ---
>> >>  arch/arm64/include/asm/efi.h            |  8 +++-----
>> >>  drivers/firmware/efi/libstub/arm-stub.c |  5 ++---
>> >>  drivers/firmware/efi/libstub/efistub.h  |  1 -
>> >>  drivers/firmware/efi/libstub/fdt.c      | 23 +++++++++++++----------
>> >>  4 files changed, 18 insertions(+), 19 deletions(-)
>> >>
>> >> diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
>> >> index ef572206f1c3..bd513dd663b9 100644
>> >> --- a/arch/arm64/include/asm/efi.h
>> >> +++ b/arch/arm64/include/asm/efi.h
>> >> @@ -39,12 +39,10 @@ extern void efi_init(void);
>> >>  /* arch specific definitions used by the stub code */
>> >>
>> >>  /*
>> >> - * AArch64 requires the DTB to be 8-byte aligned in the first 512MiB from
>> >> - * start of kernel and may not cross a 2MiB boundary. We set alignment to
>> >> - * 2MiB so we know it won't cross a 2MiB boundary.
>> >> + * AArch64 requires the DTB to be 8-byte aligned and not exceed 2MiB in size.
>> >>   */
>> >> -#define EFI_FDT_ALIGN        SZ_2M   /* used by allocate_new_fdt_and_exit_boot() */
>> >> -#define MAX_FDT_OFFSET       SZ_512M
>> >> +#define EFI_FDT_ALIGN                8
>> >> +#define EFI_FDT_MAX_SIZE     SZ_2M
>> >
>> > Is there any way we can organise things so we can share the kernel's
>> > MAX_FDT_SIZE definition, so as to keep the stub and kernel in sync?
>> >
>>
>> I'll put MAX_FDT_SIZE in asm/page.h (unless you can propose a better place)
>> That way, both fixmap.h and efi.h can refer to it.
>
> Using page.h feels a little weird, but I can't see that a better header
> exists currently.
>
> We could add asm/boot.h for things related to boot protocol that we want
> to have shareable with the stub, but I can't see anything else that we'd
> want to put in there at the moment. If there are other things we could
> deduplicate it would probably make sense, but it seems overkill for a
> single definition. :/
>

I was going to add '#define MIN_FDT_ALIGN 8' to it as well, and refer
to it from efi.h.

I think asm/boot.h is not so bad actually.