coresight: cti: Add CPU idle pm notifer to CTI devices

Adds a notify callback for CPU PM events to the CTI driver - for
CPU bound CTI devices.
Signed-off-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Link: https://lore.kernel.org/r/20200518180242.7916-24-mathieu.poirier@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-cti.c

@@ -8,6 +8,7 @@
 #include <linux/atomic.h>
 #include <linux/bits.h>
 #include <linux/coresight.h>
+#include <linux/cpu_pm.h>
 #include <linux/cpuhotplug.h>
 #include <linux/device.h>
 #include <linux/io.h>
@@ -656,6 +657,70 @@ static void cti_remove_conn_xrefs(struct cti_drvdata *drvdata)
 	}
 }
 
+/** cti PM callbacks **/
+static int cti_cpu_pm_notify(struct notifier_block *nb, unsigned long cmd,
+			     void *v)
+{
+	struct cti_drvdata *drvdata;
+	unsigned int cpu = smp_processor_id();
+	int notify_res = NOTIFY_OK;
+
+	if (!cti_cpu_drvdata[cpu])
+		return NOTIFY_OK;
+
+	drvdata = cti_cpu_drvdata[cpu];
+
+	if (WARN_ON_ONCE(drvdata->ctidev.cpu != cpu))
+		return NOTIFY_BAD;
+
+	spin_lock(&drvdata->spinlock);
+
+	switch (cmd) {
+	case CPU_PM_ENTER:
+		/* CTI regs all static - we have a copy & nothing to save */
+		drvdata->config.hw_powered = false;
+		if (drvdata->config.hw_enabled)
+			coresight_disclaim_device(drvdata->base);
+		break;
+
+	case CPU_PM_ENTER_FAILED:
+		drvdata->config.hw_powered = true;
+		if (drvdata->config.hw_enabled) {
+			if (coresight_claim_device(drvdata->base))
+				drvdata->config.hw_enabled = false;
+		}
+		break;
+
+	case CPU_PM_EXIT:
+		/* write hardware registers to re-enable. */
+		drvdata->config.hw_powered = true;
+		drvdata->config.hw_enabled = false;
+
+		/* check enable reference count to enable HW */
+		if (atomic_read(&drvdata->config.enable_req_count)) {
+			/* check we can claim the device as we re-power */
+			if (coresight_claim_device(drvdata->base))
+				goto cti_notify_exit;
+
+			drvdata->config.hw_enabled = true;
+			cti_write_all_hw_regs(drvdata);
+		}
+		break;
+
+	default:
+		notify_res = NOTIFY_DONE;
+		break;
+	}
+
+cti_notify_exit:
+	spin_unlock(&drvdata->spinlock);
+	return notify_res;
+}
+
+static struct notifier_block cti_cpu_pm_nb = {
+	.notifier_call = cti_cpu_pm_notify,
+};
+
 /* CPU HP handlers */
 static int cti_starting_cpu(unsigned int cpu)
 {
@@ -687,6 +752,8 @@ static void cti_pm_release(struct cti_drvdata *drvdata)
 {
 	if (drvdata->ctidev.cpu >= 0) {
 		if (--nr_cti_cpu == 0) {
+			cpu_pm_unregister_notifier(&cti_cpu_pm_nb);
+
 			cpuhp_remove_state_nocalls(
 				CPUHP_AP_ARM_CORESIGHT_CTI_STARTING);
 		}
@@ -815,6 +882,8 @@ static int cti_probe(struct amba_device *adev, const struct amba_id *id)
 				"arm/coresight_cti:starting",
 				cti_starting_cpu, cti_dying_cpu);
 
+			if (!ret)
+				ret = cpu_pm_register_notifier(&cti_cpu_pm_nb);
 			cpus_read_unlock();
 			if (ret)
 				goto err_out;