[PATCH] powerpc: set some low memory contents to 0 early

[Olof Johansson]

The little-endian code adds some code path to __start, which essentially ends
up adding memory contents in low memory that didn't use to be there.

That seems to have triggered a latent bug, either in firmware or kernel, where
the 64-bit word located at physical address 8 needs to be 0.

The simple hack for this right now is to write it to 0 after we're done
executing it, which is what this patch does. Unfortunately I no longer
seem to have a working JTAG setup nor firmware sources, so debugging
this down to root cause might be more trouble than it's worth given the
relatively simple workaround.

Signed-off-by: Olof Johansson <olof@xxxxxxxxx>
---
 arch/powerpc/kernel/head_64.S |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 2ae41ab..437d8bd 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -69,6 +69,13 @@ _GLOBAL(__start)
 	/* NOP this out unconditionally */
 BEGIN_FTR_SECTION
 	FIXUP_ENDIAN
+	/* Hack for PWRficient platforms: Due to CFE(?) bug, the 64-bit
+	 * word at 0x8 needs to be set to 0. Patch it up here once we're
+	 * done executing it (we can be lazy and avoid invalidating
+	 * icache)
+	 */
+	li	r0,0
+	std	0,8(0)
 	b	.__start_initialization_multiplatform
 END_FTR_SECTION(0, 1)
 
-- 
1.7.10.4

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