linux-kernel - [PATCH v2 03/12] coresight-funnel: Defer probe when associated CPUs are offline

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Message-Id: <20251218-cpu_cluster_component_pm-v2-3-2335a6ae62a0@oss.qualcomm.com>
Date: Thu, 18 Dec 2025 00:09:43 -0800
From: Yuanfang Zhang <yuanfang.zhang@....qualcomm.com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
        Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@...aro.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Leo Yan <leo.yan@...ux.dev>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: kernel@....qualcomm.com, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        Yuanfang Zhang <yuanfang.zhang@....qualcomm.com>,
        maulik.shah@....qualcomm.com
Subject: [PATCH v2 03/12] coresight-funnel: Defer probe when associated
 CPUs are offline

Per-cluster funnels 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 funnels that fail to probe due to offline CPUs in a global
   list.
2. Register a CPU hotplug notifier (funnel_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@....qualcomm.com>
---
 drivers/hwtracing/coresight/coresight-funnel.c | 62 +++++++++++++++++++++++---
 1 file changed, 57 insertions(+), 5 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
index a1264df84ab4c625c63dfbb9b7710b983a10c6b4..5d114ce1109f4f9a8b108110bdae258f216881d8 100644
--- a/drivers/hwtracing/coresight/coresight-funnel.c
+++ b/drivers/hwtracing/coresight/coresight-funnel.c
@@ -32,6 +32,9 @@
 #define FUNNEL_ENSx_MASK	0xff
 
 DEFINE_CORESIGHT_DEVLIST(funnel_devs, "funnel");
+static LIST_HEAD(funnel_delay_probe);
+static enum cpuhp_state hp_online;
+static DEFINE_SPINLOCK(delay_lock);
 
 /**
  * struct funnel_drvdata - specifics associated to a funnel component
@@ -42,6 +45,8 @@ DEFINE_CORESIGHT_DEVLIST(funnel_devs, "funnel");
  * @priority:	port selection order.
  * @spinlock:	serialize enable/disable operations.
  * @supported_cpus:	Represent the CPUs related to this funnel.
+ * @dev:	pointer to the device associated with this funnel.
+ * @link:	list node for adding this funnel to the delayed probe list.
  */
 struct funnel_drvdata {
 	void __iomem		*base;
@@ -51,6 +56,8 @@ struct funnel_drvdata {
 	unsigned long		priority;
 	raw_spinlock_t		spinlock;
 	struct cpumask		*supported_cpus;
+	struct device		*dev;
+	struct list_head	link;
 };
 
 struct funnel_smp_arg {
@@ -371,7 +378,7 @@ static int funnel_probe(struct device *dev, struct resource *res)
 		drvdata->supported_cpus = funnel_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,
@@ -379,10 +386,15 @@ static int funnel_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, &funnel_delay_probe);
+			cpus_read_unlock();
 			return 0;
+		}
+
+		cpus_read_unlock();
 	} else if (res) {
 		funnel_clear_self_claim_tag(drvdata);
 	}
@@ -394,9 +406,12 @@ static int funnel_remove(struct device *dev)
 {
 	struct funnel_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;
 }
 
@@ -533,8 +548,41 @@ static struct amba_driver dynamic_funnel_driver = {
 	.id_table	= dynamic_funnel_ids,
 };
 
+static int funnel_online_cpu(unsigned int cpu)
+{
+	struct funnel_drvdata *drvdata, *tmp;
+	int ret;
+
+	list_for_each_entry_safe(drvdata, tmp, &funnel_delay_probe, link) {
+		if (cpumask_test_cpu(cpu, drvdata->supported_cpus)) {
+			scoped_guard(spinlock,  &delay_lock)
+				list_del(&drvdata->link);
+
+			ret = pm_runtime_resume_and_get(drvdata->dev);
+			if (ret < 0)
+				return 0;
+
+			funnel_clear_self_claim_tag(drvdata);
+			funnel_add_coresight_dev(drvdata->dev);
+			pm_runtime_put(drvdata->dev);
+		}
+	}
+	return 0;
+}
+
 static int __init funnel_init(void)
 {
+	int ret;
+
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"arm/coresight-funnel:online",
+					funnel_online_cpu, NULL);
+
+	if (ret > 0)
+		hp_online = ret;
+	else
+		return ret;
+
 	return coresight_init_driver("funnel", &dynamic_funnel_driver, &funnel_driver,
 				     THIS_MODULE);
 }
@@ -542,6 +590,10 @@ static int __init funnel_init(void)
 static void __exit funnel_exit(void)
 {
 	coresight_remove_driver(&dynamic_funnel_driver, &funnel_driver);
+	if (hp_online) {
+		cpuhp_remove_state_nocalls(hp_online);
+		hp_online = 0;
+	}
 }
 
 module_init(funnel_init);

-- 
2.34.1