[PATCH] drm: Add high-precision time to vblank trace event

[Heinrich]

Store the timestamp of the current vblank in the new field 'time' of the
vblank trace event. If the timestamp is calculated by a driver that
supports high-precision vblank timing, set the field 'high-prec' to
'true'.

User space can now access actual hardware vblank times via the tracing
infrastructure. Tracing applications (such as GPUVis, see [0] for
related discussion), can use the newly added information to conduct a
more accurate analysis of display timing.

[0] https://github.com/mikesart/gpuvis/issues/30

Signed-off-by: Heinrich <heinrich.fink at daqri.com>
---
 drivers/gpu/drm/drm_trace.h  | 14 ++++++++++----
 drivers/gpu/drm/drm_vblank.c |  3 ++-
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/drm_trace.h b/drivers/gpu/drm/drm_trace.h
index baccc63db106..45f21d7fcfa1 100644
--- a/drivers/gpu/drm/drm_trace.h
+++ b/drivers/gpu/drm/drm_trace.h
@@ -11,17 +11,23 @@
 #define TRACE_INCLUDE_FILE drm_trace
 
 TRACE_EVENT(drm_vblank_event,
-	    TP_PROTO(int crtc, unsigned int seq),
-	    TP_ARGS(crtc, seq),
+	    TP_PROTO(int crtc, unsigned int seq, ktime_t time, bool high_prec),
+	    TP_ARGS(crtc, seq, time, high_prec),
 	    TP_STRUCT__entry(
 		    __field(int, crtc)
 		    __field(unsigned int, seq)
+		    __field(ktime_t, time)
+		    __field(bool, high_prec)
 		    ),
 	    TP_fast_assign(
 		    __entry->crtc = crtc;
 		    __entry->seq = seq;
-		    ),
-	    TP_printk("crtc=%d, seq=%u", __entry->crtc, __entry->seq)
+		    __entry->time = time;
+		    __entry->high_prec = high_prec;
+			),
+	    TP_printk("crtc=%d, seq=%u, time=%lld, high-prec=%s",
+			__entry->crtc, __entry->seq, __entry->time,
+			__entry->high_prec ? "true" : "false")
 );
 
 TRACE_EVENT(drm_vblank_event_queued,
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index a1b65d26d761..fb089a88b516 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -1706,7 +1706,8 @@ static void drm_handle_vblank_events(struct drm_device *dev, unsigned int pipe)
 		send_vblank_event(dev, e, seq, now);
 	}
 
-	trace_drm_vblank_event(pipe, seq);
+	trace_drm_vblank_event(pipe, seq, now,
+			dev->driver->get_vblank_timestamp != NULL);
 }
 
 /**
-- 
2.23.0.rc1