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-rw-r--r--include/asm-powerpc/ppc_asm.h6
1 files changed, 6 insertions, 0 deletions
diff --git a/include/asm-powerpc/ppc_asm.h b/include/asm-powerpc/ppc_asm.h
index 2dbd4e7884f..ef96bfd4ef4 100644
--- a/include/asm-powerpc/ppc_asm.h
+++ b/include/asm-powerpc/ppc_asm.h
@@ -356,6 +356,12 @@ END_FTR_SECTION_IFCLR(CPU_FTR_601)
#define toreal(rd)
#define fromreal(rd)
+/*
+ * We use addis to ensure compatibility with the "classic" ppc versions of
+ * these macros, which use rs = 0 to get the tophys offset in rd, rather than
+ * converting the address in r0, and so this version has to do that too
+ * (i.e. set register rd to 0 when rs == 0).
+ */
#define tophys(rd,rs) \
addis rd,rs,0