perf/core: Introduce perf_get_pmu_by_node API

Add a new public API to fetch a pointer to struct pmu from a devicetree
node devicetree node. This is meant to be used by other drivers to
create in-kernel counter for custom hardware PMUs with automatically
allocated pmu->type.

This is implementated by adding a new "parent_dev" field which pmu
drivers can optionally fill. This parent device is set as the parent of
the pmu->dev created on the pmu_bus. This also has the nice side-effect
of creating additional symlinks inside sysfs.

The actual per_get_pmu_by_node function is implemented through
bus_find_device and callers are asked to "put_device(pmu->dev)" when
done. This might cause problems if pmu_bus is initialize late but
consumers should handle errors by returning -EPROBE_DEFER anyway.
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>

drivers/perf/arm_pmu_platform.c

@@ -202,6 +202,7 @@ int arm_pmu_device_probe(struct platform_device *pdev,
 		return -ENOMEM;
 
 	pmu->plat_device = pdev;
+	pmu->pmu.parent_dev = &pdev->dev;
 
 	ret = pmu_parse_irqs(pmu);
 	if (ret)

drivers/perf/fsl_imx8_ddr_perf.c

@@ -673,6 +673,7 @@ static int ddr_perf_probe(struct platform_device *pdev)
 		goto ddr_perf_err;
 	}
 
+	pmu->pmu.parent_dev = &pdev->dev;
 	ret = perf_pmu_register(&pmu->pmu, name, -1);
 	if (ret)
 		goto ddr_perf_err;

include/linux/perf_event.h

@@ -271,6 +271,7 @@ struct pmu {
 
 	struct module			*module;
 	struct device			*dev;
+	struct device			*parent_dev;
 	const struct attribute_group	**attr_groups;
 	const struct attribute_group	**attr_update;
 	const char			*name;
@@ -937,6 +938,14 @@ extern void perf_event_itrace_started(struct perf_event *event);
 extern int perf_pmu_register(struct pmu *pmu, const char *name, int type);
 extern void perf_pmu_unregister(struct pmu *pmu);
 
+#ifdef CONFIG_OF
+extern struct pmu* perf_get_pmu_by_node(struct device_node *node);
+#else
+static inline struct pmu* perf_get_pmu_by_node(struct device_node *node) {
+	return NULL;
+}
+#endif
+
 extern int perf_num_counters(void);
 extern const char *perf_pmu_name(void);
 extern void __perf_event_task_sched_in(struct task_struct *prev,

kernel/events/core.c

@@ -10667,6 +10667,7 @@ static int pmu_dev_alloc(struct pmu *pmu)
 
 	dev_set_drvdata(pmu->dev, pmu);
 	pmu->dev->bus = &pmu_bus;
+	pmu->dev->parent = pmu->parent_dev;
 	pmu->dev->release = pmu_dev_release;
 	ret = device_add(pmu->dev);
 	if (ret)
@@ -10696,6 +10697,30 @@ static int pmu_dev_alloc(struct pmu *pmu)
 	goto out;
 }
 
+#ifdef CONFIG_OF
+static int perf_match_parent_of_node(struct device *dev, const void *np)
+{
+       return dev->parent && dev->parent->of_node == np;
+}
+
+/**
+ * perf_get_pmu_by_node() - Fetch PMU instance via devicetree node
+ *
+ * @node: devicetree node for PMU
+ *
+ * Caller should put_device(pmu-dev) when done.
+ */
+struct pmu* perf_get_pmu_by_node(struct device_node *node)
+{
+       struct device* dev;
+
+       dev = bus_find_device(&pmu_bus, NULL, node, perf_match_parent_of_node);
+
+       return dev ? dev_get_drvdata(dev) : NULL;
+}
+EXPORT_SYMBOL_GPL(perf_get_pmu_by_node);
+#endif
+
 static struct lock_class_key cpuctx_mutex;
 static struct lock_class_key cpuctx_lock;