powerpc/ppc476: Disable BTAC

This patch disables the branch target address CAM which under specific
circumstances may cause the processor to skip execution of 1-4
instructions. This fixes IBM Erratum #47.

Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/powerpc/kernel/head_44x.S b/arch/powerpc/kernel/head_44x.S
index c334f53453f7..b5061abbd2e0 100644
--- a/arch/powerpc/kernel/head_44x.S
+++ b/arch/powerpc/kernel/head_44x.S
@@ -1210,10 +1210,12 @@ clear_utlb_entry:
 
         /* We configure icbi to invalidate 128 bytes at a time since the
          * current 32-bit kernel code isn't too happy with icache != dcache
-         * block size
+         * block size. We also disable the BTAC as this can cause errors
+         * in some circumstances (see IBM Erratum 47).
          */
         mfspr   r3,SPRN_CCR0
         oris    r3,r3,0x0020
+        ori     r3,r3,0x0040
         mtspr   SPRN_CCR0,r3
         isync