[PATCH 1/2] powerpc/perf: Use stack siar instead of mfspr

Minor optimization in the 'perf_instruction_pointer' function code by
making use of stack siar instead of mfspr.

Fixes: 75382aa72f06 ("powerpc/perf: Move code to select SIAR or pt_regs
into perf_read_regs")
Signed-off-by: Kajol Jain <redacted>
---
 arch/powerpc/perf/core-book3s.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index bb0ee716de91..1b464aad29c4 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c

@@ -2260,7 +2260,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
 		else
 			return regs->nip;
 	} else if (use_siar && siar_valid(regs))
-		return mfspr(SPRN_SIAR) + perf_ip_adjust(regs);
+		return siar + perf_ip_adjust(regs);
 	else if (use_siar)
 		return 0;		// no valid instruction pointer
 	else

-- 
2.26.2

Incase of random sampling, there can be scenarios where SIAR is not
latching sample address and results in 0 value. Since current code
directly returning the siar value, we could see multiple instruction
pointer values as 0 in perf report.
Patch resolves this issue by adding a ternary condition to return
regs->nip incase SIAR is 0.

Fixes: 75382aa72f06 ("powerpc/perf: Move code to select SIAR or pt_regs
into perf_read_regs")
Signed-off-by: Kajol Jain <redacted>
---
 arch/powerpc/perf/core-book3s.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 1b464aad29c4..aeecaaf6810f 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c

@@ -2260,7 +2260,7 @@ unsigned long perf_instruction_pointer(struct pt_regs *regs)
 		else
 			return regs->nip;
 	} else if (use_siar && siar_valid(regs))
-		return siar + perf_ip_adjust(regs);
+		return siar ? siar + perf_ip_adjust(regs) : regs->nip;
 	else if (use_siar)
 		return 0;		// no valid instruction pointer
 	else

-- 
2.26.2