pt_config() enables tracing by allowing NMIs and pause/resume, issuing
the necessary barriers, and calling pt_config_start().  A later change
needs to re-enable tracing on a (re-)start path without repeating the
full pt_config() setup (filters, RTIT_CTL, buffer configuration).

Factor that enabling sequence out into a new helper, pt_config_enable(),
so it can be called on its own.

No functional change intended.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
 arch/x86/events/intel/pt.c | 41 ++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index b5726b50e77d..dc1be7f6e04b 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -502,6 +502,29 @@ static u64 pt_config_filters(struct perf_event *event)
 	return rtit_ctl;
 }
 
+static void pt_config_enable(struct perf_event *event)
+{
+	struct pt *pt = this_cpu_ptr(&pt_ctx);
+
+	/*
+	 * Allow resume before starting so as not to overwrite a value set by a
+	 * PMI.
+	 */
+	barrier();
+	WRITE_ONCE(pt->resume_allowed, 1);
+	/* Configuration is complete, it is now OK to handle an NMI */
+	barrier();
+	WRITE_ONCE(pt->handle_nmi, 1);
+	barrier();
+	pt_config_start(event);
+	barrier();
+	/*
+	 * Allow pause after starting so its pt_config_stop() doesn't race with
+	 * pt_config_start().
+	 */
+	WRITE_ONCE(pt->pause_allowed, 1);
+}
+
 static void pt_config(struct perf_event *event)
 {
 	struct pt *pt = this_cpu_ptr(&pt_ctx);
@@ -541,23 +564,7 @@ static void pt_config(struct perf_event *event)
 
 	event->hw.aux_config = reg;
 
-	/*
-	 * Allow resume before starting so as not to overwrite a value set by a
-	 * PMI.
-	 */
-	barrier();
-	WRITE_ONCE(pt->resume_allowed, 1);
-	/* Configuration is complete, it is now OK to handle an NMI */
-	barrier();
-	WRITE_ONCE(pt->handle_nmi, 1);
-	barrier();
-	pt_config_start(event);
-	barrier();
-	/*
-	 * Allow pause after starting so its pt_config_stop() doesn't race with
-	 * pt_config_start().
-	 */
-	WRITE_ONCE(pt->pause_allowed, 1);
+	pt_config_enable(event);
 }
 
 static void pt_config_stop(struct perf_event *event)
-- 
2.53.0