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SubjectRe: [PATCH 1/8] arm/dt: Make __vet_atags also accept a dtb image
On Tue, 18 Jan 2011, Grant Likely wrote:

> The dtb is passed to the kernel via register r2, which is the same
> method that is used to pass an atags pointer. This patch modifies
> __vet_atags to not clear r2 when it encounters a dtb image.
>
> Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
> ---
> arch/arm/kernel/head-common.S | 19 +++++++++++++------
> arch/arm/kernel/head.S | 8 ++++----
> 2 files changed, 17 insertions(+), 10 deletions(-)
>
> diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
> index 8f57515..d9a9105 100644
> --- a/arch/arm/kernel/head-common.S
> +++ b/arch/arm/kernel/head-common.S
> @@ -14,6 +14,7 @@
> #define ATAG_CORE 0x54410001
> #define ATAG_CORE_SIZE ((2*4 + 3*4) >> 2)
> #define ATAG_CORE_SIZE_EMPTY ((2*4) >> 2)
> +#define OF_DT_MAGIC 0xedfe0dd0 /* 0xd00dfeed in big-endian */

ARM can be big endian too. Would be nice to make this endian
independent, or at least list this limitation in the commit log.

> /*
> * Exception handling. Something went wrong and we can't proceed. We
> @@ -105,22 +106,28 @@ __lookup_machine_type_data:
>
> /* Determine validity of the r2 atags pointer. The heuristic requires
> * that the pointer be aligned, in the first 16k of physical RAM and
> - * that the ATAG_CORE marker is first and present. Future revisions
> + * that the ATAG_CORE marker is first and present. If CONFIG_OF_FLATTREE
> + * is selected, then it will also accept a dtb pointer. Future revisions
> * of this function may be more lenient with the physical address and
> * may also be able to move the ATAGS block if necessary.
> *
> * r8 = machinfo
> *
> * Returns:
> - * r2 either valid atags pointer, or zero
> + * r2 either valid atags pointer, valid dtb pointer, or zero
> * r5, r6 corrupted
> */
> __vet_atags:
> tst r2, #0x3 @ aligned?
> bne 1f
>
> - ldr r5, [r2, #0] @ is first tag ATAG_CORE?
> - cmp r5, #ATAG_CORE_SIZE
> +#ifdef CONFIG_OF_FLATTREE
> + ldr r5, [r2, #0] @ is it a DTB?
> + ldr r6, =OF_DT_MAGIC
> + cmp r5, r6
> + beq 2f
> +#endif
> + cmp r5, #ATAG_CORE_SIZE @ is first tag ATAG_CORE?

The "ldr r5 ..." is now done only within #ifdef CONFIG_OF_FLATTREE. So
if CONFIG_OF_FLATTREE is undefined then r5 will contain garbage.


Nicolas


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