[PATCH 3.18 06/39] powerpc/powernv: Fix opal_exit tracepoint opcode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Ellerman <mpe@ellerman.id.au>

commit a7e0fb6c2029a780444d09560f739e020d54fe4d upstream.

Currently the opal_exit tracepoint usually shows the opcode as 0:

  <idle>-0     [047] d.h.   635.654292: opal_entry: opcode=63
  <idle>-0     [047] d.h.   635.654296: opal_exit: opcode=0 retval=0
  kopald-1209  [019] d...   636.420943: opal_entry: opcode=10
  kopald-1209  [019] d...   636.420959: opal_exit: opcode=0 retval=0

This is because we incorrectly load the opcode into r0 before calling
__trace_opal_exit(), whereas it expects the opcode in r3 (first function
parameter). In fact we are leaving the retval in r3, so opcode and
retval will always show the same value.

Instead load the opcode into r3, resulting in:

  <idle>-0     [040] d.h.   636.618625: opal_entry: opcode=63
  <idle>-0     [040] d.h.   636.618627: opal_exit: opcode=63 retval=0

Fixes: c49f63530bb6 ("powernv: Add OPAL tracepoints")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/powerpc/platforms/powernv/opal-wrappers.S |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/powerpc/platforms/powernv/opal-wrappers.S
+++ b/arch/powerpc/platforms/powernv/opal-wrappers.S
@@ -148,7 +148,7 @@ opal_tracepoint_entry:
 opal_tracepoint_return:
 	std	r3,STK_REG(R31)(r1)
 	mr	r4,r3
-	ld	r0,STK_REG(R23)(r1)
+	ld	r3,STK_REG(R23)(r1)
 	bl	__trace_opal_exit
 	ld	r3,STK_REG(R31)(r1)
 	addi	r1,r1,STACKFRAMESIZE