powerpc/perf: Add regs_no_sipr()

On power8 the presence or absence of SIPR depends on settings at runtime,
so convert to using a dynamic flag for NO_SIPR. Existing backends that
set NO_SIPR unconditionally set the dynamic flag obviously.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/perf/core-book3s.c

@@ -156,6 +156,11 @@ static bool regs_sipr(struct pt_regs *regs)
 	return !!(regs->dsisr & sipr);
 }
 
+static bool regs_no_sipr(struct pt_regs *regs)
+{
+	return !!(regs->result & 2);
+}
+
 static inline u32 perf_flags_from_msr(struct pt_regs *regs)
 {
 	if (regs->msr & MSR_PR)
@@ -178,7 +183,7 @@ static inline u32 perf_get_misc_flags(struct pt_regs *regs)
 	 * SIAR which should give slightly more reliable
 	 * results
 	 */
-	if (ppmu->flags & PPMU_NO_SIPR) {
+	if (regs_no_sipr(regs)) {
 		unsigned long siar = mfspr(SPRN_SIAR);
 		if (siar >= PAGE_OFFSET)
 			return PERF_RECORD_MISC_KERNEL;
@@ -208,6 +213,10 @@ static inline void perf_read_regs(struct pt_regs *regs)
 	int use_siar;
 
 	regs->dsisr = mmcra;
+	regs->result = 0;
+
+	if (ppmu->flags & PPMU_NO_SIPR)
+		regs->result |= 2;
 
 	/*
 	 * If this isn't a PMU exception (eg a software event) the SIAR is
@@ -232,12 +241,12 @@ static inline void perf_read_regs(struct pt_regs *regs)
 		use_siar = 1;
 	else if ((ppmu->flags & PPMU_NO_CONT_SAMPLING))
 		use_siar = 0;
-	else if (!(ppmu->flags & PPMU_NO_SIPR) && regs_sipr(regs))
+	else if (!regs_no_sipr(regs) && regs_sipr(regs))
 		use_siar = 0;
 	else
 		use_siar = 1;
 
-	regs->result = use_siar;
+	regs->result |= use_siar;
 }
 
 /*