coresight: etmv4: Fix CPU power management setup in probe() function

The current probe() function calls a pair of cpuhp_xxx API functions to
setup CPU hotplug handling. The hotplug lock is held for the duration of
the two calls and other CPU related code using cpus_read_lock() /
cpus_read_unlock() calls.

The problem is that on error states, goto: statements bypass the
cpus_read_unlock() call. This code has increased in complexity as the
driver has developed.

This patch introduces a pair of helper functions etm4_pm_setup_cpuslocked()
and etm4_pm_clear() which correct the issues above and group the PM code a
little better.

The two functions etm4_cpu_pm_register() and etm4_cpu_pm_unregister() are
dropped as these call cpu_pm_register_notifier() / ..unregister_notifier()
dependent on CONFIG_CPU_PM - but this define is used to nop these functions
out in the pm headers - so the wrapper functions are superfluous.

Fixes: f188b5e7 ("coresight: etm4x: Save/restore state across CPU low power states")
Fixes: e9f5d63f ("hwtracing/coresight-etm4x: Use cpuhp_setup_state_nocalls_cpuslocked()")
Fixes: 58eb457b ("hwtracing/coresight-etm4x: Convert to hotplug state machine")
Signed-off-by: Mike Leach <mike.leach@linaro.org>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200701160852.2782823-3-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-etm4x.c

@@ -1388,18 +1388,57 @@ static struct notifier_block etm4_cpu_pm_nb = {
 	.notifier_call = etm4_cpu_pm_notify,
 };
 
-static int etm4_cpu_pm_register(void)
+/* Setup PM. Called with cpus locked. Deals with error conditions and counts */
+static int etm4_pm_setup_cpuslocked(void)
 {
-	if (IS_ENABLED(CONFIG_CPU_PM))
-		return cpu_pm_register_notifier(&etm4_cpu_pm_nb);
+	int ret;
 
-	return 0;
+	if (etm4_count++)
+		return 0;
+
+	ret = cpu_pm_register_notifier(&etm4_cpu_pm_nb);
+	if (ret)
+		goto reduce_count;
+
+	ret = cpuhp_setup_state_nocalls_cpuslocked(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,
+						   "arm/coresight4:online",
+						   etm4_online_cpu, NULL);
+
+	/* HP dyn state ID returned in ret on success */
+	if (ret > 0) {
+		hp_online = ret;
+		return 0;
+	}
+
+	/* failed dyn state - remove others */
+	cpuhp_remove_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING);
+
+unregister_notifier:
+	cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
+
+reduce_count:
+	--etm4_count;
+	return ret;
 }
 
-static void etm4_cpu_pm_unregister(void)
+static void etm4_pm_clear(void)
 {
-	if (IS_ENABLED(CONFIG_CPU_PM))
-		cpu_pm_unregister_notifier(&etm4_cpu_pm_nb);
+	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) {
+		cpuhp_remove_state_nocalls(hp_online);
+		hp_online = 0;
+	}
 }
 
 static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
@@ -1453,24 +1492,15 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 				etm4_init_arch_data,  drvdata, 1))
 		dev_err(dev, "ETM arch init failed\n");
 
-	if (!etm4_count++) {
-		cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ARM_CORESIGHT_STARTING,
-						     "arm/coresight4:starting",
-						     etm4_starting_cpu, etm4_dying_cpu);
-		ret = cpuhp_setup_state_nocalls_cpuslocked(CPUHP_AP_ONLINE_DYN,
-							   "arm/coresight4:online",
-							   etm4_online_cpu, NULL);
-		if (ret < 0)
-			goto err_arch_supported;
-		hp_online = ret;
+	ret = etm4_pm_setup_cpuslocked();
+	cpus_read_unlock();
 
-		ret = etm4_cpu_pm_register();
-		if (ret)
-			goto err_arch_supported;
+	/* etm4_pm_setup_cpuslocked() does its own cleanup - exit on error */
+	if (ret) {
+		etmdrvdata[drvdata->cpu] = NULL;
+		return ret;
 	}
 
-	cpus_read_unlock();
-
 	if (etm4_arch_supported(drvdata->arch) == false) {
 		ret = -EINVAL;
 		goto err_arch_supported;
@@ -1517,13 +1547,7 @@ static int etm4_probe(struct amba_device *adev, const struct amba_id *id)
 
 err_arch_supported:
 	etmdrvdata[drvdata->cpu] = NULL;
-	if (--etm4_count == 0) {
-		etm4_cpu_pm_unregister();
-
-		cpuhp_remove_state_nocalls(CPUHP_AP_ARM_CORESIGHT_STARTING);
-		if (hp_online)
-			cpuhp_remove_state_nocalls(hp_online);
-	}
+	etm4_pm_clear();
 	return ret;
 }