coresight: core: Fix coresight device probe failure issue

It is possibe that probe failure issue happens when the device
and its child_device's probe happens at the same time.
In coresight_make_links, has_conns_grp is true for parent, but
has_conns_grp is false for child device as has_conns_grp is set
to true in coresight_create_conns_sysfs_group. The probe of parent
device will fail at this condition. Add has_conns_grp check for
child device before make the links and make the process from
device_register to connection_create be atomic to avoid this
probe failure issue.

Cc: stable@vger.kernel.org
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Suggested-by: Mike Leach <mike.leach@linaro.org>
Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
Link: https://lore.kernel.org/r/20220309142206.15632-1-quic_jinlmao@quicinc.com
[ Added Cc stable ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>

drivers/hwtracing/coresight/coresight-core.c

@@ -1379,7 +1379,7 @@ static int coresight_fixup_device_conns(struct coresight_device *csdev)
 			continue;
 		conn->child_dev =
 			coresight_find_csdev_by_fwnode(conn->child_fwnode);
-		if (conn->child_dev) {
+		if (conn->child_dev && conn->child_dev->has_conns_grp) {
 			ret = coresight_make_links(csdev, conn,
 						   conn->child_dev);
 			if (ret)
@@ -1571,6 +1571,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	int nr_refcnts = 1;
 	atomic_t *refcnts = NULL;
 	struct coresight_device *csdev;
+	bool registered = false;
 
 	csdev = kzalloc(sizeof(*csdev), GFP_KERNEL);
 	if (!csdev) {
@@ -1591,7 +1592,8 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
 	if (!refcnts) {
 		ret = -ENOMEM;
-		goto err_free_csdev;
+		kfree(csdev);
+		goto err_out;
 	}
 
 	csdev->refcnt = refcnts;
@@ -1616,6 +1618,13 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
 	dev_set_name(&csdev->dev, "%s", desc->name);
 
+	/*
+	 * Make sure the device registration and the connection fixup
+	 * are synchronised, so that we don't see uninitialised devices
+	 * on the coresight bus while trying to resolve the connections.
+	 */
+	mutex_lock(&coresight_mutex);
+
 	ret = device_register(&csdev->dev);
 	if (ret) {
 		put_device(&csdev->dev);
@@ -1623,7 +1632,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 		 * All resources are free'd explicitly via
 		 * coresight_device_release(), triggered from put_device().
 		 */
-		goto err_out;
+		goto out_unlock;
 	}
 
 	if (csdev->type == CORESIGHT_DEV_TYPE_SINK ||
@@ -1638,11 +1647,11 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 			 * from put_device(), which is in turn called from
 			 * function device_unregister().
 			 */
-			goto err_out;
+			goto out_unlock;
 		}
 	}
-
-	mutex_lock(&coresight_mutex);
+	/* Device is now registered */
+	registered = true;
 
 	ret = coresight_create_conns_sysfs_group(csdev);
 	if (!ret)
@@ -1652,16 +1661,18 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
 	if (!ret && cti_assoc_ops && cti_assoc_ops->add)
 		cti_assoc_ops->add(csdev);
 
+out_unlock:
 	mutex_unlock(&coresight_mutex);
-	if (ret) {
+	/* Success */
+	if (!ret)
+		return csdev;
+
+	/* Unregister the device if needed */
+	if (registered) {
 		coresight_unregister(csdev);
 		return ERR_PTR(ret);
 	}
 
-	return csdev;
-
-err_free_csdev:
-	kfree(csdev);
 err_out:
 	/* Cleanup the connection information */
 	coresight_release_platform_data(NULL, desc->pdata);