ARM: perf: only register a CPU PMU when present

Currently, an "empty" struct pmu is registered as the CPU PMU,
regardless of whether there is a physical PMU. This burdens the
accessor functions with checks to see whether a PMU is actually
present.

This patch changes initialisation to register a PMU only if there is a
supported PMU present, and removes the checks that this change makes
redundant.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Reviewed-by: Jamie Iles <jamie@jamieiles.com>
Reviewed-by: Ashwin Chaugule <ashwinc@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 2 insertions, 16 deletions

diff --git a/arch/arm/kernel/perf_event.c b/arch/arm/kernel/perf_event.c
index 5d60c9c25964..753648cf9af6 100644
--- a/arch/arm/kernel/perf_event.c
+++ b/arch/arm/kernel/perf_event.c
@@ -250,9 +250,6 @@ armpmu_stop(struct perf_event *event, int flags)
 {
         struct hw_perf_event *hwc = &event->hw;
 
-        if (!armpmu)
-                return;
-
         /*
          * ARM pmu always has to update the counter, so ignore
          * PERF_EF_UPDATE, see comments in armpmu_start().
@@ -270,9 +267,6 @@ armpmu_start(struct perf_event *event, int flags)
 {
         struct hw_perf_event *hwc = &event->hw;
 
-        if (!armpmu)
-                return;
-
         /*
          * ARM pmu always has to reprogram the period, so ignore
          * PERF_EF_RELOAD, see the comment below.
@@ -567,9 +561,6 @@ static int armpmu_event_init(struct perf_event *event)
                 return -ENOENT;
         }
 
-        if (!armpmu)
-                return -ENODEV;
-
         event->destroy = hw_perf_event_destroy;
 
         if (!atomic_inc_not_zero(&active_events)) {
@@ -599,9 +590,6 @@ static void armpmu_enable(struct pmu *pmu)
         int idx, enabled = 0;
         struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
 
-        if (!armpmu)
-                return;
-
         for (idx = 0; idx < armpmu->num_events; ++idx) {
                 struct perf_event *event = cpuc->events[idx];
 
@@ -618,8 +606,7 @@ static void armpmu_enable(struct pmu *pmu)
 
 static void armpmu_disable(struct pmu *pmu)
 {
-        if (armpmu)
-                armpmu->stop();
+        armpmu->stop();
 }
 
 static struct pmu pmu = {
@@ -738,12 +725,11 @@ init_hw_perf_events(void)
         if (armpmu) {
                 pr_info("enabled with %s PMU driver, %d counters available\n",
                         armpmu->name, armpmu->num_events);
+                perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
         } else {
                 pr_info("no hardware support available\n");
         }
 
-        perf_pmu_register(&pmu, "cpu", PERF_TYPE_RAW);
-
         return 0;
 }
 early_initcall(init_hw_perf_events);