Prior to Armv8.4, the feature FEAT_TRF is not supported by Arm CPUs.
Consequently, the sysfs node 'ts_source' will not be set as 1 by the
CoreSight ETM driver.  On the other hand, the perf tool relies on the
'ts_source' node to determine whether the kernel timestamp is traced.
Since the 'ts_source' is not set for Arm CPUs prior to Armv8.4,
platforms in this case cannot utilize the traced timestamp as the kernel
time.

This patch enables the 'T' itrace option, which forcibly utilizes the
traced timestamp as the kernel time.  If users are aware that their
working platform's Arm CoreSight shares the same counter with the kernel
time, they can specify 'T' option to decode the traced timestamp as the
kernel time.

An usage example is:

  # perf record -e cs_etm// -- test_program
  # perf script --itrace=i10ibT
  # perf report --itrace=i10ibT
Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20231014074513.1668000-3-leo.yan@linaro.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>