perf pmus: Create placholder regardless of scanning core_only

If scanning all PMUs the placeholder is still necessary if no core PMU
is found. This situation occurs in perf test's parse-events test,
when uncore events appear before core.

Fixes: 628eaa4e ("perf pmus: Add placeholder core PMU")
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: Thomas Richter <tmricht@linux.ibm.com>
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: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@amd.com>
Cc: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230706183705.601412-1-irogers@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/pmus.c

@@ -152,16 +152,14 @@ static void pmu_read_sysfs(bool core_only)
 	}
 
 	closedir(dir);
-	if (core_only) {
-		if (!list_empty(&core_pmus))
-			read_sysfs_core_pmus = true;
-		else {
-			if (perf_pmu__create_placeholder_core_pmu(&core_pmus))
-				read_sysfs_core_pmus = true;
-		}
-	} else {
+	if (list_empty(&core_pmus)) {
+		if (!perf_pmu__create_placeholder_core_pmu(&core_pmus))
+			pr_err("Failure to set up any core PMUs\n");
+	}
+	if (!list_empty(&core_pmus)) {
 		read_sysfs_core_pmus = true;
-		read_sysfs_all_pmus = true;
+		if (!core_only)
+			read_sysfs_all_pmus = true;
 	}
 }