[PATCH v2 2/3] perf jevents: Make the model argument optional

[TAKANO Mitsuhiro <takano32@gmail.com>]

The model argument carries a default of "all", but a positional argument
with a default and no nargs is still required: "jevents.py x86 <dir>" exits
with "the following arguments are required: model", and so does any caller
that only wants the tables for an architecture.

Make it nargs='?' so the default is reachable and an omitted model means
"all".  Builds pass it explicitly, so the generated tables do not change.

Fixes: 5a09b1fd1b1f ("perf jevents: Add model list option")
Signed-off-by: TAKANO Mitsuhiro <takano32@gmail.com>
---
 tools/perf/pmu-events/jevents.py | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
index 86060a228b75..844fa82887bb 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -1486,10 +1486,10 @@ def main() -> None:
 
   ap = argparse.ArgumentParser()
   ap.add_argument('arch', help='Architecture name like x86')
-  ap.add_argument('model', help='''Select a model such as skylake to
-reduce the code size.  Normally set to "all". For architectures like
-ARM64 with an implementor/model, the model must include the implementor
-such as "arm/cortex-a34".''',
+  ap.add_argument('model', nargs='?', help='''Select a model such as skylake to
+reduce the code size.  Normally set to "all", and that is what an omitted
+model means. For architectures like ARM64 with an implementor/model, the
+model must include the implementor such as "arm/cortex-a34".''',
                   default='all')
   ap.add_argument(
       'starting_dir',
-- 
2.53.0