On 04/22/2013 05:11 AM, Michael Ellerman wrote:

On Thu, Apr 18, 2013 at 05:56:12PM +0530, Anshuman Khandual wrote:

quoted

This patch adds new POWER8 instruction encoding for reading
the BHRB buffer entries and also clearing it. Encoding for
"clrbhrb" instruction is straight forward.

Which is "clear branch history rolling buffer" ?

quoted

But "mfbhrbe"
encoding involves reading a certain index of BHRB buffer
into a particular GPR register.

And "Move from branch history rolling buffer entry" ?

Sure, would add these descriptions in the change log.

quoted

diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
index 8752bc8..93ae5a1 100644
--- a/arch/powerpc/include/asm/ppc-opcode.h
+++ b/arch/powerpc/include/asm/ppc-opcode.h

@@ -82,6 +82,7 @@
 #define	__REGA0_R31	31
 
 /* sorted alphabetically */
+#define PPC_INST_BHRBE			0x7c00025c

I don't think you really need this, just use the literal value below.

quoted

@@ -297,6 +298,12 @@
 #define PPC_NAP			stringify_in_c(.long PPC_INST_NAP)
 #define PPC_SLEEP		stringify_in_c(.long PPC_INST_SLEEP)
 
+/* BHRB instructions */
+#define PPC_CLRBHRB		stringify_in_c(.long 0x7c00035c)
+#define PPC_MFBHRBE(r, n)	stringify_in_c(.long PPC_INST_BHRBE | \
+						__PPC_RS(r) | \
+							(((n) & 0x1f) << 11))

Why are you not using ___PPC_RB(n) here ?

I would replace __PPC_RS(r) with __PPC_RT(r) which makes more sense from
instruction encoding point of view.

Regards
Anshuman