[PATCH] arm64: expose kernel page size in Image header flags

[Suzuki K. Poulose]

On 17/09/15 10:32, Ard Biesheuvel wrote:
> In order for a bootloader to be able to decide whether a certain
> arm64 kernel image is compatible with the hardware it is running
> on, it needs to be able to find out for which page size the kernel
> was built. This is necessary, since the architecture does not
> mandate support for all page sizes it defines, and the kernel cannot
> boot to a state where it can print a diagnostic if it was built for
> a page size that is not supported by the hardware.
>
> So assign two bits in the flags field of the Image header, and set
> them according to the build time page size. For backward compatibility,
> retain the 0b00 value as 'unspecified'.
>
> Acked-by: Catalin Marinas <catalin.marinas at arm.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

Ard,

I picked this patch based on the our initial discussion on 16K page size
series, and added it to the V2 of the series.

	https://lkml.org/lkml/2015/9/15/716


> ---
>   Documentation/arm64/booting.txt | 3 ++-
>   arch/arm64/kernel/image.h       | 4 +++-
>   2 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
> index 1690350f16e7..46056e7d766e 100644
> --- a/Documentation/arm64/booting.txt
> +++ b/Documentation/arm64/booting.txt
> @@ -104,7 +104,8 @@ Header notes:
>   - The flags field (introduced in v3.17) is a little-endian 64-bit field
>     composed as follows:
>     Bit 0: 	Kernel endianness.  1 if BE, 0 if LE.
> -  Bits 1-63:	Reserved.
> +  Bits 1-2:	Kernel page size.   0=unspecified, 1=4K, 2=16K, 3=64K
> +  Bits 3-63:	Reserved.
>
>   - When image_size is zero, a bootloader should attempt to keep as much
>     memory as possible free for use by the kernel immediately after the
> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
> index 8fae0756e175..5def289bda84 100644
> --- a/arch/arm64/kernel/image.h
> +++ b/arch/arm64/kernel/image.h
> @@ -47,7 +47,9 @@
>   #define __HEAD_FLAG_BE	0
>   #endif
>
> -#define __HEAD_FLAGS	(__HEAD_FLAG_BE << 0)
> +#define __HEAD_FLAG_PAGE_SIZE ((PAGE_SHIFT - 10) / 2)
> +
> +#define __HEAD_FLAGS	(__HEAD_FLAG_BE << 0) | (__HEAD_FLAG_PAGE_SIZE << 1)
>

FWIW,

	Tested-by: Suzuki K. Poulose <suzuki.poulose at arm.com>


Thanks
Suzuki