Re: [PATCH] MIPS: Octeon: byteswap initramfs in little endian mode

[David Daney <ddaney@caviumnetworks.com>]

On 05/05/2016 02:33 PM, Aurelien Jarno wrote:
> The initramfs if loaded in memory by U-Boot running in big endian mode.
> When the kernel is running in little endian mode, we need to byteswap it
> as it is accessed byte by byte.

Ouch!

Really it should be fixed in the bootloader, but that probably won't happen.

I wonder, is there a magic number that the initrd has?  If so, we could 
probe for a byteswapped initrd and not do the byte reversal unconditionally.

The logic seems correct, we need to byte swap each 8-byte aligned 8-byte 
word in the image.

>
> Cc: David Daney <david.daney@cavium.com>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>   arch/mips/kernel/setup.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
>
> Note: It might not be the best place to byteswap the initramfs not the
> best way to do it. At least it shows the problem and what shoudl be done.
> Suggestions to improve the patch are welcome.
>
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 4f60734..e7d015e 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -263,6 +263,16 @@ static void __init finalize_initrd(void)
>   		goto disable;
>   	}
>
> +#if defined(CONFIG_CPU_CAVIUM_OCTEON) && defined(CONFIG_CPU_LITTLE_ENDIAN)
> +	{
> +		unsigned long i;
> +		pr_info("Cavium Octeon kernel in little endian mode "
> +			"detected, byteswapping ramdisk\n");
> +		for (i = initrd_start; i < ALIGN(initrd_end, 8); i += 8)
> +			*((unsigned long *)i) = swab64(*((unsigned long *)i));
> +	}
> +#endif
> +
>   	reserve_bootmem(__pa(initrd_start), size, BOOTMEM_DEFAULT);
>   	initrd_below_start_ok = 1;
>
>