From: Xu Yang <xu.yang_2@nxp.com>

When do perf stat on sys metric, perf tool output nothing now:
$ perf stat -a -M imx95_ddr_read.all -I 1000
$

This command runs on an arm64 machine and the Soc has one DDR hw pmu
except one armv8_cortex_a55 pmu. Their maps show as follows:

const struct pmu_events_map pmu_events_map[] = {
{
	.arch = "arm64",
	.cpuid = "0x00000000410fd050",
	.event_table = {
		.pmus = pmu_events__arm_cortex_a55,
		.num_pmus = ARRAY_SIZE(pmu_events__arm_cortex_a55)
	},
	.metric_table = {
		.pmus = NULL,
		.num_pmus = 0
	}
},

static const struct pmu_sys_events pmu_sys_event_tables[] = {
{
	.event_table = {
		.pmus = pmu_events__freescale_imx95_sys,
		.num_pmus = ARRAY_SIZE(pmu_events__freescale_imx95_sys)
	},
	.metric_table = {
		.pmus = pmu_metrics__freescale_imx95_sys,
		.num_pmus = ARRAY_SIZE(pmu_metrics__freescale_imx95_sys)
	},
	.name = "pmu_events__freescale_imx95_sys",
},

Currently, pmu_metrics_table__find() will return NULL when only do perf
stat on sys metric. Then parse_groups() will never be called to parse
sys metric_name, finally perf tool will exit directly. This should be a
common problem. To fix the issue, this will keep the logic before commit
f20c15d13f01 ("perf pmu-events: Remember the perf_events_map for a PMU")
to return a empty metric table rather than a NULL pointer. This should
be fine since the removed part just check if the table match provided
metric_name. Without these code, the code in parse_groups() will also
check the validity of metrci_name too.

Fixes: f20c15d13f01 ("perf pmu-events: Remember the perf_events_map for a PMU")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Acked-by: Ian Rogers <irogers@google.com>
Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/perf/pmu-events/empty-pmu-events.c | 12 +-----------
 tools/perf/pmu-events/jevents.py         | 12 +-----------
 2 files changed, 2 insertions(+), 22 deletions(-)

diff --git a/tools/perf/pmu-events/empty-pmu-events.c b/tools/perf/pmu-events/empty-pmu-events.c
index 2b7516946ded..b8719dab264d 100644
--- a/tools/perf/pmu-events/empty-pmu-events.c
+++ b/tools/perf/pmu-events/empty-pmu-events.c
@@ -585,17 +585,7 @@ const struct pmu_metrics_table *perf_pmu__find_metrics_table(struct perf_pmu *pm
         if (!map)
                 return NULL;
 
-        if (!pmu)
-                return &map->metric_table;
-
-        for (size_t i = 0; i < map->metric_table.num_pmus; i++) {
-                const struct pmu_table_entry *table_pmu = &map->metric_table.pmus[i];
-                const char *pmu_name = &big_c_string[table_pmu->pmu_name.offset];
-
-                if (pmu__name_match(pmu, pmu_name))
-                           return &map->metric_table;
-        }
-        return NULL;
+	return &map->metric_table;
 }
 
 const struct pmu_events_table *find_core_events_table(const char *arch, const char *cpuid)
diff --git a/tools/perf/pmu-events/jevents.py b/tools/perf/pmu-events/jevents.py
index 6e71b09dbc2a..70f4fd5395fb 100755
--- a/tools/perf/pmu-events/jevents.py
+++ b/tools/perf/pmu-events/jevents.py
@@ -1101,17 +1101,7 @@ const struct pmu_metrics_table *perf_pmu__find_metrics_table(struct perf_pmu *pm
         if (!map)
                 return NULL;
 
-        if (!pmu)
-                return &map->metric_table;
-
-        for (size_t i = 0; i < map->metric_table.num_pmus; i++) {
-                const struct pmu_table_entry *table_pmu = &map->metric_table.pmus[i];
-                const char *pmu_name = &big_c_string[table_pmu->pmu_name.offset];
-
-                if (pmu__name_match(pmu, pmu_name))
-                           return &map->metric_table;
-        }
-        return NULL;
+	return &map->metric_table;
 }
 
 const struct pmu_events_table *find_core_events_table(const char *arch, const char *cpuid)
-- 
2.47.0.199.ga7371fff76-goog