coresight: etm4x: add CPU hotplug support for probing

etm4x devices cannot be successfully probed when their CPU is offline.
For example, when booting with maxcpus=n, ETM probing will fail on
CPUs >n, and the probing won't be reattempted once the CPUs come
online. This will leave those CPUs unable to make use of ETM.

This change adds a mechanism to delay the probing if the corresponding
CPU is offline, and to try it again when the CPU comes online.

Signed-off-by: Tamas Zsoldos <tamas.zsoldos@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20220705145935.24679-1-tamas.zsoldos@arm.com

drivers/hwtracing/coresight/coresight-etm4x-core.c

@@ -66,10 +66,13 @@ static enum cpuhp_state hp_online;
 
 struct etm4_init_arg {
 	unsigned int		pid;
-	struct etmv4_drvdata	*drvdata;
+	struct device		*dev;
 	struct csdev_access	*csa;
 };
 
+static DEFINE_PER_CPU(struct etm4_init_arg *, delayed_probe);
+static int etm4_probe_cpu(unsigned int cpu);
+
 /*
  * Check if TRCSSPCICRn(i) is implemented for a given instance.
  *
@@ -1085,7 +1088,7 @@ static void etm4_init_arch_data(void *info)
 	struct csdev_access *csa;
 	int i;
 
-	drvdata = init_arg->drvdata;
+	drvdata = dev_get_drvdata(init_arg->dev);
 	csa = init_arg->csa;
 
 	/*
@@ -1528,7 +1531,7 @@ void etm4_config_trace_mode(struct etmv4_config *config)
 static int etm4_online_cpu(unsigned int cpu)
 {
 	if (!etmdrvdata[cpu])
-		return 0;
+		return etm4_probe_cpu(cpu);
 
 	if (etmdrvdata[cpu]->boot_enable && !etmdrvdata[cpu]->sticky_enable)
 		coresight_enable(etmdrvdata[cpu]->csdev);
@@ -1904,48 +1907,20 @@ static void etm4_pm_clear(void)
 	}
 }
 
-static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
+static int etm4_add_coresight_dev(struct etm4_init_arg *init_arg)
 {
 	int ret;
 	struct coresight_platform_data *pdata = NULL;
-	struct etmv4_drvdata *drvdata;
+	struct device *dev = init_arg->dev;
+	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev);
 	struct coresight_desc desc = { 0 };
-	struct etm4_init_arg init_arg = { 0 };
 	u8 major, minor;
 	char *type_name;
 
-	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
 	if (!drvdata)
-		return -ENOMEM;
+		return -EINVAL;
 
-	dev_set_drvdata(dev, drvdata);
+	desc.access = *init_arg->csa;
-
-	if (pm_save_enable == PARAM_PM_SAVE_FIRMWARE)
-		pm_save_enable = coresight_loses_context_with_cpu(dev) ?
-			       PARAM_PM_SAVE_SELF_HOSTED : PARAM_PM_SAVE_NEVER;
-
-	if (pm_save_enable != PARAM_PM_SAVE_NEVER) {
-		drvdata->save_state = devm_kmalloc(dev,
-				sizeof(struct etmv4_save_state), GFP_KERNEL);
-		if (!drvdata->save_state)
-			return -ENOMEM;
-	}
-
-	drvdata->base = base;
-
-	spin_lock_init(&drvdata->spinlock);
-
-	drvdata->cpu = coresight_get_cpu(dev);
-	if (drvdata->cpu < 0)
-		return drvdata->cpu;
-
-	init_arg.drvdata = drvdata;
-	init_arg.csa = &desc.access;
-	init_arg.pid = etm_pid;
-
-	if (smp_call_function_single(drvdata->cpu,
-				etm4_init_arch_data,  &init_arg, 1))
-		dev_err(dev, "ETM arch init failed\n");
 
 	if (!drvdata->arch)
 		return -EINVAL;
@@ -2016,6 +1991,68 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
 	return 0;
 }
 
+static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
+{
+	struct etmv4_drvdata *drvdata;
+	struct csdev_access access = { 0 };
+	struct etm4_init_arg init_arg = { 0 };
+	struct etm4_init_arg *delayed;
+
+	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	dev_set_drvdata(dev, drvdata);
+
+	if (pm_save_enable == PARAM_PM_SAVE_FIRMWARE)
+		pm_save_enable = coresight_loses_context_with_cpu(dev) ?
+			       PARAM_PM_SAVE_SELF_HOSTED : PARAM_PM_SAVE_NEVER;
+
+	if (pm_save_enable != PARAM_PM_SAVE_NEVER) {
+		drvdata->save_state = devm_kmalloc(dev,
+				sizeof(struct etmv4_save_state), GFP_KERNEL);
+		if (!drvdata->save_state)
+			return -ENOMEM;
+	}
+
+	drvdata->base = base;
+
+	spin_lock_init(&drvdata->spinlock);
+
+	drvdata->cpu = coresight_get_cpu(dev);
+	if (drvdata->cpu < 0)
+		return drvdata->cpu;
+
+	init_arg.dev = dev;
+	init_arg.csa = &access;
+	init_arg.pid = etm_pid;
+
+	/*
+	 * Serialize against CPUHP callbacks to avoid race condition
+	 * between the smp call and saving the delayed probe.
+	 */
+	cpus_read_lock();
+	if (smp_call_function_single(drvdata->cpu,
+				etm4_init_arch_data,  &init_arg, 1)) {
+		/* The CPU was offline, try again once it comes online. */
+		delayed = devm_kmalloc(dev, sizeof(*delayed), GFP_KERNEL);
+		if (!delayed) {
+			cpus_read_unlock();
+			return -ENOMEM;
+		}
+
+		*delayed = init_arg;
+
+		per_cpu(delayed_probe, drvdata->cpu) = delayed;
+
+		cpus_read_unlock();
+		return 0;
+	}
+	cpus_read_unlock();
+
+	return etm4_add_coresight_dev(&init_arg);
+}
+
 static int etm4_probe_amba(struct amba_device *adev, const struct amba_id *id)
 {
 	void __iomem *base;
@@ -2054,6 +2091,35 @@ static int etm4_probe_platform_dev(struct platform_device *pdev)
 	return ret;
 }
 
+static int etm4_probe_cpu(unsigned int cpu)
+{
+	int ret;
+	struct etm4_init_arg init_arg;
+	struct csdev_access access = { 0 };
+	struct etm4_init_arg *iap = *this_cpu_ptr(&delayed_probe);
+
+	if (!iap)
+		return 0;
+
+	init_arg = *iap;
+	devm_kfree(init_arg.dev, iap);
+	*this_cpu_ptr(&delayed_probe) = NULL;
+
+	ret = pm_runtime_resume_and_get(init_arg.dev);
+	if (ret < 0) {
+		dev_err(init_arg.dev, "Failed to get PM runtime!\n");
+		return 0;
+	}
+
+	init_arg.csa = &access;
+	etm4_init_arch_data(&init_arg);
+
+	etm4_add_coresight_dev(&init_arg);
+
+	pm_runtime_put(init_arg.dev);
+	return 0;
+}
+
 static struct amba_cs_uci_id uci_id_etm4[] = {
 	{
 		/*  ETMv4 UCI data */
@@ -2068,16 +2134,20 @@ static void clear_etmdrvdata(void *info)
 	int cpu = *(int *)info;
 
 	etmdrvdata[cpu] = NULL;
+	per_cpu(delayed_probe, cpu) = NULL;
 }
 
 static int __exit etm4_remove_dev(struct etmv4_drvdata *drvdata)
 {
-	etm_perf_symlink(drvdata->csdev, false);
+	bool had_delayed_probe;
 	/*
 	 * Taking hotplug lock here to avoid racing between etm4_remove_dev()
 	 * and CPU hotplug call backs.
 	 */
 	cpus_read_lock();
+
+	had_delayed_probe = per_cpu(delayed_probe, drvdata->cpu);
+
 	/*
 	 * The readers for etmdrvdata[] are CPU hotplug call backs
 	 * and PM notification call backs. Change etmdrvdata[i] on
@@ -2085,12 +2155,15 @@ static int __exit etm4_remove_dev(struct etmv4_drvdata *drvdata)
 	 * inside one call back function.
 	 */
 	if (smp_call_function_single(drvdata->cpu, clear_etmdrvdata, &drvdata->cpu, 1))
-		etmdrvdata[drvdata->cpu] = NULL;
+		clear_etmdrvdata(&drvdata->cpu);
 
 	cpus_read_unlock();
 
-	cscfg_unregister_csdev(drvdata->csdev);
+	if (!had_delayed_probe) {
-	coresight_unregister(drvdata->csdev);
+		etm_perf_symlink(drvdata->csdev, false);
+		cscfg_unregister_csdev(drvdata->csdev);
+		coresight_unregister(drvdata->csdev);
+	}
 
 	return 0;
 }