coresight: etm4x: Fix etm4_count race by moving cpuhp callbacks to init

etm4_count keeps track of number of ETMv4 registered and on some systems,
a race is observed on etm4_count variable which can lead to multiple calls
to cpuhp_setup_state_nocalls_cpuslocked(). This function internally calls
cpuhp_store_callbacks() which prevents multiple registrations of callbacks
for a given state and due to this race, it returns -EBUSY leading to ETM
probe failures like below.

 coresight-etm4x: probe of 7040000.etm failed with error -16

This race can easily be triggered with async probe by setting probe type
as PROBE_PREFER_ASYNCHRONOUS and with ETM power management property
"arm,coresight-loses-context-with-cpu".

Prevent this race by moving cpuhp callbacks to etm driver init since the
cpuhp callbacks doesn't have to depend on the etm4_count and can be once
setup during driver init. Similarly we move cpu_pm notifier registration
to driver init and completely remove etm4_count usage. Also now we can
use non cpuslocked version of cpuhp callbacks with this movement.

Fixes: 9b6a3f36 ("coresight: etmv4: Fix CPU power management setup in probe() function")
Fixes: 58eb457b ("hwtracing/coresight-etm4x: Convert to hotplug state machine")
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200916191737.4001561-2-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm4x.c

@@ -48,8 +48,6 @@ module_param(pm_save_enable, int, 0444);
 MODULE_PARM_DESC(pm_save_enable,
 	"Save/restore state on power down: 1 = never, 2 = self-hosted");
 
-/* The number of ETMv4 currently registered */
-static int etm4_count;
 static struct etmv4_drvdata *etmdrvdata[NR_CPUS];
 static void etm4_set_default_config(struct etmv4_config *config);
 static int etm4_set_event_filters(struct etmv4_drvdata *drvdata,
@@ -1397,26 +1395,23 @@ static struct notifier_block etm4_cpu_pm_nb = {
 	.notifier_call = etm4_cpu_pm_notify,
 };
 
-/* Setup PM. Called with cpus locked. Deals with error conditions and counts */
-static int etm4_pm_setup_cpuslocked(void)
+/* Setup PM. Deals with error conditions and counts */
+static int __init etm4_pm_setup(void)
 {
 	int ret;
 
-	if (etm4_count++)
-		return 0;
-
 	ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb);
 	if (ret)
-		goto reduce_count;
+		return ret;
 
-	ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING,
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING,
 					"arm/coresight4:starting",
 					etm4_starting_cpu, etm4_dying_cpu);
 
 	if (ret)
 		goto unregister_notifier;
 
-	ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
+	ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
 					"arm/coresight4:online",
 					etm4_online_cpu, NULL);
 
@@ -1427,21 +1422,15 @@ static int etm4_pm_setup_cpuslocked(void)
 	}
 
 	/* failed dyn state - remove others */
-	cpuhp_remove_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING);
+	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
 
 unregister_notifier:
 	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
-
-reduce_count:
-	--etm4_count;
 	return ret;
 }
 
-static void etm4_pm_clear(void)
+static void __init etm4_pm_clear(void)
 {
-	if (--etm4_count != 0)
-		return;
-
 	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
 	cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
 	if (hp_online) {
@@ -1497,22 +1486,12 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 	if (!desc.name)
 		return -ENOMEM;
 
-	cpus_read_lock();
 	etmdrvdata[drvdata->cpu] = drvdata;
 
 	if (smp_call_function_single(drvdata->cpu,
 				etm4_init_arch_data,  drvdata, 1))
 		dev_err(dev, "ETM arch init failed\n");
 
-	ret = etm4_pm_setup_cpuslocked();
-	cpus_read_unlock();
-
-	/* etm4_pm_setup_cpuslocked() does its own cleanup - exit on error */
-	if (ret) {
-		etmdrvdata[drvdata->cpu] = NULL;
-		return ret;
-	}
-
 	if (etm4_arch_supported(drvdata->arch) == false) {
 		ret = -EINVAL;
 		goto err_arch_supported;
@@ -1559,7 +1538,6 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 
 err_arch_supported:
 	etmdrvdata[drvdata->cpu] = NULL;
-	etm4_pm_clear();
 	return ret;
 }
 
@@ -1597,4 +1575,23 @@ static struct amba_driver etm4x_driver = {
 	.probe		= etm4_probe,
 	.id_table	= etm4_ids,
 };
-builtin_amba_driver(etm4x_driver);
+
+static int __init etm4x_init(void)
+{
+	int ret;
+
+	ret = etm4_pm_setup();
+
+	/* etm4_pm_setup() does its own cleanup - exit on error */
+	if (ret)
+		return ret;
+
+	ret = amba_driver_register(&etm4x_driver);
+	if (ret) {
+		pr_err("Error registering etm4x driver\n");
+		etm4_pm_clear();
+	}
+
+	return ret;
+}
+device_initcall(etm4x_init);