Hi Nicolas,

On Tue, Jan 18, 2011 at 2:26 PM, Nicolas Pitre [off-list ref] wrote:

On Tue, 18 Jan 2011, Grant Likely wrote:

quoted

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 <redacted>
---
?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.

How about:
#ifdef CONFIG_CPU_BIG_ENDIAN
#define OF_DT_MAGIC 0xd00dfeed
#else
#define OF_DT_MAGIC 0xedfe0dd0 /* 0xd00dfeed in big-endian */
#endif

Or is there a better way for loading and comparing big endian values in ARM?

quoted

?/*
? * 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.

Oops, that was a silly oversight.  Fixed now.

g.

Nicolas

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.