trace-read: parse high-precision timestamp from drm_vblank_event

When reading drm_vblank_event events, parse the following optional
fields:

- 'time': a possibly more accurate timestamp better representing the
actual HW vblank timestamp

- 'high_prec': true if 'time' is a high-precision HW timestamp from a
drm driver with this particular capability

Fields are only parsed if the ftrace clock was set to `mono`, otherwise
the timestamps can't be aligned in a meaningful way.

With ftrace, the tracing clock can be set to `mono like this:

`echo mono > /sys/kernel/tracing/trace_clock`

Also add helper functions to retrieve the high-precision timestamp.

src/trace-cmd/trace-read.cpp

@@ -1575,6 +1575,8 @@ class trace_data_t
         ftrace_function_str = strpool.getstr( "ftrace-function" );
         drm_vblank_event_str = strpool.getstr( "drm_vblank_event" );
         sched_switch_str = strpool.getstr( "sched_switch" );
+        time_str = strpool.getstr( "time" );
+        high_prec_str = strpool.getstr( "high_prec" );
     }
 
 public:
@@ -1593,6 +1595,8 @@ class trace_data_t
     const char *ftrace_function_str;
     const char *drm_vblank_event_str;
     const char *sched_switch_str;
+    const char *time_str;
+    const char *high_prec_str;
 };
 
 static void init_event_flags( trace_data_t &trace_data, trace_event_t &event )
@@ -1727,6 +1731,30 @@ static int trace_enum_events( trace_data_t &trace_data, tracecmd_input_t *handle
 
                     trace_event.crtc = val;
                 }
+                else if ( trace_event.name == trace_data.drm_vblank_event_str &&
+                          format_name == trace_data.time_str &&
+                          !strcmp(handle->pevent->trace_clock, "mono"))
+                {
+                    // for drm_vblank_event, if "time" field is available,
+                    // and the trace-clock is monotonic, store the timestamp
+                    // passed along with the vblank event
+                    unsigned long long val = pevent_read_number( pevent,
+                               ( char * )record->data + format->offset, format->size );
+
+                    trace_event.vblank_ts = val - trace_data.trace_info.min_file_ts;
+                }
+                else if ( trace_event.name == trace_data.drm_vblank_event_str &&
+                          format_name == trace_data.high_prec_str &&
+                          !strcmp(handle->pevent->trace_clock, "mono"))
+                {
+                    // for drm_vblank_event, if "high_prec" field is available,
+                    // and the trace-lock is monotonic, store the field whether or not
+                    // the passed timestamp is actually from a high-precision source
+                    unsigned long long val = pevent_read_number( pevent,
+                               ( char * )record->data + format->offset, format->size );
+
+                    trace_event.vblank_ts_high_prec = val != 0;
+                }
                 else if ( is_ftrace_function )
                 {
                     bool is_ip = ( format_name == trace_data.ip_str );

src/trace-cmd/trace-read.h

@@ -178,16 +178,18 @@ struct trace_event_t
 public:
     bool is_filtered_out = false;
 
-    int pid;                        // event process id
-    uint32_t id;                    // event id
-    uint32_t cpu;                   // cpu this event was hit on
-    int64_t ts;                     // timestamp
-
-    uint32_t flags = 0;             // TRACE_FLAGS_IRQS_OFF, TRACE_FLAG_HARDIRQ, TRACE_FLAG_SOFTIRQ
-    uint32_t seqno = 0;             // event seqno (from fields)
-    uint32_t id_start = INVALID_ID; // start event if this is a graph sequence event (ie amdgpu_sched_run_job, fence_signaled)
+    int pid;                          // event process id
+    uint32_t id;                      // event id
+    uint32_t cpu;                     // cpu this event was hit on
+    int64_t ts;                       // timestamp
+
+    uint32_t flags = 0;               // TRACE_FLAGS_IRQS_OFF, TRACE_FLAG_HARDIRQ, TRACE_FLAG_SOFTIRQ
+    uint32_t seqno = 0;               // event seqno (from fields)
+    uint32_t id_start = INVALID_ID;   // start event if this is a graph sequence event (ie amdgpu_sched_run_job, fence_signaled)
     uint32_t graph_row_id = 0;
-    int crtc = -1;                  // drm_vblank_event crtc (or -1)
+    int crtc = -1;                    // drm_vblank_event crtc (or -1)
+    int64_t vblank_ts = INT64_MAX;    // time-stamp that is passed with the drm_event_vblank event
+    bool vblank_ts_high_prec = false; // denotes whether or not the hardware timestamp is high-precision
 
     uint32_t color = 0;             // color of the event (or 0 for default)
 
@@ -207,13 +209,14 @@ struct trace_event_t
     event_field_t *fields = nullptr;
 
 public:
-    bool is_fence_signaled() const  { return !!( flags & TRACE_FLAG_FENCE_SIGNALED ); }
-    bool is_ftrace_print() const    { return !!( flags & TRACE_FLAG_FTRACE_PRINT ); }
-    bool is_vblank() const          { return !!( flags & TRACE_FLAG_VBLANK ); }
-    bool is_timeline() const        { return !!( flags & TRACE_FLAG_TIMELINE ); }
-    bool is_sched_switch() const    { return !!( flags & TRACE_FLAG_SCHED_SWITCH ); }
-
-    bool has_duration() const       { return duration != INT64_MAX; }
+    bool is_fence_signaled() const             { return !!( flags & TRACE_FLAG_FENCE_SIGNALED ); }
+    bool is_ftrace_print() const               { return !!( flags & TRACE_FLAG_FTRACE_PRINT ); }
+    bool is_vblank() const                     { return !!( flags & TRACE_FLAG_VBLANK ); }
+    bool is_timeline() const                   { return !!( flags & TRACE_FLAG_TIMELINE ); }
+    bool is_sched_switch() const               { return !!( flags & TRACE_FLAG_SCHED_SWITCH ); }
+
+    bool has_duration() const                  { return duration != INT64_MAX; }
+    int64_t get_vblank_ts(bool want_high_prec) const { return want_high_prec && (vblank_ts != INT64_MAX) && vblank_ts_high_prec ? vblank_ts : ts; }
 
     const char *get_timeline_name( const char *def = NULL ) const
     {