perf cs-etm: Treat NO_SYNC element as trace discontinuity

The CoreSight tracer driver might insert barrier packets between
different buffers, thus the decoder can spot the boundaries based on the
barrier packet; it is possible for the decoder to hit a barrier packet
and emit a NO_SYNC element, then the decoder will find a periodic
synchronisation point inside that next trace block that starts the trace
again but does not have the TRACE_ON element as indicator - usually
because this trace block has wrapped the buffer so we have lost the
original point when the trace was enabled.

In the first case it causes the insertion of a OCSD_GEN_TRC_ELEM_NO_SYNC
in the middle of the tracing stream, but as we were not handling the
NO_SYNC element properly this ends up making users miss the
discontinuity indications.

Though OCSD_GEN_TRC_ELEM_NO_SYNC is different from CS_ETM_TRACE_ON when
output from the decoder, both indicate that the trace data is
discontinuous; this patch treats OCSD_GEN_TRC_ELEM_NO_SYNC as a trace
discontinuity and generates a CS_ETM_DISCONTINUITY packet for it, so
cs-etm can handle the discontinuity for this case, finally it saves the
last trace data for the previous trace block and restart samples for the
new block.

Signed-off-by: Leo Yan <[email protected]>
Reviewed-by: Mathieu Poirier <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mike Leach <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Robert Walker <[email protected]>
Cc: coresight ml <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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