[PATCH v2 10/12] coresight-tmc: Defer probe when associated CPUs are offline

[Yuanfang Zhang]

On some platforms, the TMC driver may probe before the associated CPUs
are online. This prevents the driver from securely accessing the
hardware or configuring it via smp_call_function_single(), which
requires the target CPU to be available.

To address this, defer the hardware initialization if the associated
CPUs are offline:
1. Track such deferred devices in a global list.
2. Register a CPU hotplug callback (`tmc_online_cpu`) to detect when
   a relevant CPU comes online.
3. Upon CPU online, retry the hardware initialization and registration
   for the waiting TMC devices.

Signed-off-by: Yuanfang Zhang <yuanfang.zhang at oss.qualcomm.com>
---
 drivers/hwtracing/coresight/coresight-tmc-core.c | 59 +++++++++++++++++++++++-
 drivers/hwtracing/coresight/coresight-tmc.h      |  4 ++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index 5b9f2e57c78f42f0f1460d8a8dcbac72b5f6085e..9182fa8e4074a7c9739494b2f5d59be2e96f1d3d 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-core.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
@@ -36,6 +36,9 @@
 DEFINE_CORESIGHT_DEVLIST(etb_devs, "tmc_etb");
 DEFINE_CORESIGHT_DEVLIST(etf_devs, "tmc_etf");
 DEFINE_CORESIGHT_DEVLIST(etr_devs, "tmc_etr");
+static LIST_HEAD(tmc_delay_probe);
+static enum cpuhp_state hp_online;
+static DEFINE_SPINLOCK(delay_lock);
 
 int tmc_wait_for_tmcready(struct tmc_drvdata *drvdata)
 {
@@ -1027,6 +1030,8 @@ static int __tmc_probe(struct device *dev, struct resource *res)
 		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,
@@ -1034,11 +1039,16 @@ static int __tmc_probe(struct device *dev, struct resource *res)
 			if (!ret)
 				break;
 		}
-		cpus_read_unlock();
+
 		if (ret) {
+			scoped_guard(spinlock,  &delay_lock)
+				list_add(&drvdata->link, &tmc_delay_probe);
+			cpus_read_unlock();
 			ret = 0;
 			goto out;
 		}
+
+		cpus_read_unlock();
 	} else {
 		tmc_init_hw_config(drvdata);
 	}
@@ -1103,8 +1113,12 @@ static void __tmc_remove(struct device *dev)
 		misc_deregister(&drvdata->miscdev);
 	if (drvdata->crashdev.fops)
 		misc_deregister(&drvdata->crashdev);
-	if (drvdata->csdev)
+	if (drvdata->csdev) {
 		coresight_unregister(drvdata->csdev);
+	} else {
+		scoped_guard(spinlock,  &delay_lock)
+			list_del(&drvdata->link);
+	}
 }
 
 static void tmc_remove(struct amba_device *adev)
@@ -1215,14 +1229,55 @@ static struct platform_driver tmc_platform_driver = {
 	},
 };
 
+static int tmc_online_cpu(unsigned int cpu)
+{
+	struct tmc_drvdata *drvdata, *tmp;
+	int ret;
+
+	spin_lock(&delay_lock);
+	list_for_each_entry_safe(drvdata, tmp, &tmc_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;
+
+			tmc_init_hw_config(drvdata);
+			tmc_clear_self_claim_tag(drvdata);
+			tmc_add_coresight_dev(drvdata->dev);
+			pm_runtime_put(drvdata->dev);
+			spin_lock(&delay_lock);
+		}
+	}
+	spin_unlock(&delay_lock);
+	return 0;
+}
+
 static int __init tmc_init(void)
 {
+	int ret;
+
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"arm/coresight-tmc:online",
+					tmc_online_cpu, NULL);
+
+	if (ret > 0)
+		hp_online = ret;
+	else
+		return ret;
+
 	return coresight_init_driver("tmc", &tmc_driver, &tmc_platform_driver, THIS_MODULE);
 }
 
 static void __exit tmc_exit(void)
 {
 	coresight_remove_driver(&tmc_driver, &tmc_platform_driver);
+	if (hp_online) {
+		cpuhp_remove_state_nocalls(hp_online);
+		hp_online = 0;
+	}
 }
 module_init(tmc_init);
 module_exit(tmc_exit);
diff --git a/drivers/hwtracing/coresight/coresight-tmc.h b/drivers/hwtracing/coresight/coresight-tmc.h
index b104b7bf82d2a7a99382636e41d3718cf258d820..2583bc4f556195cd814e674dc66f08909dea61b2 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.h
+++ b/drivers/hwtracing/coresight/coresight-tmc.h
@@ -246,6 +246,8 @@ struct tmc_resrv_buf {
  * @supported_cpus:	Represent the CPUs related to this TMC.
  * @devid:	TMC variant ID inferred from the device configuration register.
  * @desc_name:	Name to be used while creating crash interface.
+ * @dev:	pointer to the device associated with this TMC.
+ * @link:	link to the delay_probed list.
  */
 struct tmc_drvdata {
 	struct clk		*atclk;
@@ -279,6 +281,8 @@ struct tmc_drvdata {
 	struct cpumask		*supported_cpus;
 	u32			devid;
 	const char		*desc_name;
+	struct device		*dev;
+	struct list_head	link;
 };
 
 struct etr_buf_operations {

-- 
2.34.1