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

Yuanfang Zhang
2025-12-18T08:10:54Z

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@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