[PATCH v2 05/12] coresight-replicator: Defer probe when associated CPUs are offline

[Yuanfang Zhang <yuanfang.zhang@oss.qualcomm.com>]

Per-cluster replicators rely on the associated CPU cluster being online
to securely access registers during initialization. If all CPUs in the
cluster are offline during probe, these operations fail.

Support deferred initialization for these devices:
1. Track replicators that fail to probe due to offline CPUs in a global
   list.
2. Register a CPU hotplug notifier (`replicator_online_cpu`) to detect
   when a relevant CPU comes online.
3. Upon CPU online, retry the hardware initialization and registration
   with the CoreSight framework.

Signed-off-by: Yuanfang Zhang <yuanfang.zhang@oss.qualcomm.com>
---
 drivers/hwtracing/coresight/coresight-replicator.c | 65 ++++++++++++++++++++--
 1 file changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-replicator.c b/drivers/hwtracing/coresight/coresight-replicator.c
index c11da452559c73af6709b39d03b646cb4779736f..f8d13894098f1e414fb0da8d6eeb1da4f0d55a8c 100644
--- a/drivers/hwtracing/coresight/coresight-replicator.c
+++ b/drivers/hwtracing/coresight/coresight-replicator.c
@@ -26,6 +26,9 @@
 #define REPLICATOR_IDFILTER1		0x004
 
 DEFINE_CORESIGHT_DEVLIST(replicator_devs, "replicator");
+static LIST_HEAD(replicator_delay_probe);
+static enum cpuhp_state hp_online;
+static DEFINE_SPINLOCK(delay_lock);
 
 /**
  * struct replicator_drvdata - specifics associated to a replicator component
@@ -37,6 +40,8 @@ DEFINE_CORESIGHT_DEVLIST(replicator_devs, "replicator");
  * @spinlock:	serialize enable/disable operations.
  * @check_idfilter_val: check if the context is lost upon clock removal.
  * @supported_cpus:	Represent the CPUs related to this funnel.
+ * @dev:	pointer to the device associated with this replicator.
+ * @link:	link to the delay_probed list.
  */
 struct replicator_drvdata {
 	void __iomem		*base;
@@ -46,6 +51,8 @@ struct replicator_drvdata {
 	raw_spinlock_t		spinlock;
 	bool			check_idfilter_val;
 	struct cpumask		*supported_cpus;
+	struct device		*dev;
+	struct list_head	link;
 };
 
 struct replicator_smp_arg {
@@ -394,7 +401,7 @@ static int replicator_probe(struct device *dev, struct resource *res)
 		drvdata->supported_cpus = replicator_get_supported_cpus(dev);
 		if (!drvdata->supported_cpus)
 			return -EINVAL;
-
+		drvdata->dev = dev;
 		cpus_read_lock();
 		for_each_cpu(cpu, drvdata->supported_cpus) {
 			ret = smp_call_function_single(cpu,
@@ -402,10 +409,15 @@ static int replicator_probe(struct device *dev, struct resource *res)
 			if (!ret)
 				break;
 		}
-		cpus_read_unlock();
 
-		if (ret)
+		if (ret) {
+			scoped_guard(spinlock,  &delay_lock)
+				list_add(&drvdata->link, &replicator_delay_probe);
+			cpus_read_unlock();
 			return 0;
+		}
+
+		cpus_read_unlock();
 	} else if (res) {
 		replicator_init_hw(drvdata);
 	}
@@ -419,8 +431,13 @@ static int replicator_remove(struct device *dev)
 {
 	struct replicator_drvdata *drvdata = dev_get_drvdata(dev);
 
-	if (drvdata->csdev)
+	if (drvdata->csdev) {
 		coresight_unregister(drvdata->csdev);
+	} else {
+		scoped_guard(spinlock,  &delay_lock)
+			list_del(&drvdata->link);
+	}
+
 	return 0;
 }
 
@@ -552,8 +569,44 @@ static struct amba_driver dynamic_replicator_driver = {
 	.id_table	= dynamic_replicator_ids,
 };
 
+static int replicator_online_cpu(unsigned int cpu)
+{
+	struct replicator_drvdata *drvdata, *tmp;
+	int ret;
+
+	spin_lock(&delay_lock);
+	list_for_each_entry_safe(drvdata, tmp, &replicator_delay_probe, link) {
+		if (cpumask_test_cpu(cpu, drvdata->supported_cpus)) {
+			list_del(&drvdata->link);
+			spin_unlock(&delay_lock);
+			ret = pm_runtime_resume_and_get(drvdata->dev);
+			if (ret < 0)
+				return 0;
+
+			replicator_clear_self_claim_tag(drvdata);
+			replicator_reset(drvdata);
+			replicator_add_coresight_dev(drvdata->dev);
+			pm_runtime_put(drvdata->dev);
+			spin_lock(&delay_lock);
+		}
+	}
+	spin_unlock(&delay_lock);
+	return 0;
+}
+
 static int __init replicator_init(void)
 {
+	int ret;
+
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"arm/coresight-replicator:online",
+					replicator_online_cpu, NULL);
+
+	if (ret > 0)
+		hp_online = ret;
+	else
+		return ret;
+
 	return coresight_init_driver("replicator", &dynamic_replicator_driver, &replicator_driver,
 				     THIS_MODULE);
 }
@@ -561,6 +614,10 @@ static int __init replicator_init(void)
 static void __exit replicator_exit(void)
 {
 	coresight_remove_driver(&dynamic_replicator_driver, &replicator_driver);
+	if (hp_online) {
+		cpuhp_remove_state_nocalls(hp_online);
+		hp_online = 0;
+	}
 }
 
 module_init(replicator_init);

-- 
2.34.1