[PATCH v5 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>
---
v5: patch 3 says which keys a table may carry and checks the tree
    against that list, replacing the near-miss report that v4 had.
    The list is 51 names, 47 of which jevents.py reads; an architecture
    that is not there or is named as a path is an error (status 2)
    instead of a silent pass, and an object written without the list
    brackets is reported.  The name of a metricgroup is not treated as
    a key.  jsonschema is not used because perf's build would then
    require it, and the list holds the same names a schema would.
    The target is check-jevents, next to check-headers, and takes
    JEVENTS_CHECK_ARCH; a shell test covers a reported key, a clean
    tree and a missing architecture.

 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 61f778dcc1e5..f4dca47eb49b 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