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

From: Olof Johansson
Date: Fri Jan 03 2014 - 03:09:28 EST

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 */
+ /* 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


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