Messages in this thread | | | Date | Tue, 18 Jan 2011 16:26:17 -0500 (EST) | From | Nicolas Pitre <> | Subject | Re: [PATCH 1/8] arm/dt: Make __vet_atags also accept a dtb image |
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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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