PCI: endpoint: Fix NULL pointer dereference error when CONFIGFS is disabled

commit ef1433f7 ("PCI: endpoint: Create configfs entry for each
pci_epf_device_id table entry") while adding configfs entry for each
pci_epf_device_id table entry introduced a NULL pointer dereference error
when CONFIG_PCI_ENDPOINT_CONFIGFS is not enabled.

Fix it here.

Fixes: ef1433f7 ("PCI: endpoint: Create configfs entry for each
pci_epf_device_id table entry")
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
[lorenzo.pieralisi: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/endpoint/pci-epf-core.c

@@ -137,6 +137,20 @@ void *pci_epf_alloc_space(struct pci_epf *epf, size_t size, enum pci_barno bar)
 }
 EXPORT_SYMBOL_GPL(pci_epf_alloc_space);
 
+static void pci_epf_remove_cfs(struct pci_epf_driver *driver)
+{
+	struct config_group *group, *tmp;
+
+	if (!IS_ENABLED(CONFIG_PCI_ENDPOINT_CONFIGFS))
+		return;
+
+	mutex_lock(&pci_epf_mutex);
+	list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry)
+		pci_ep_cfs_remove_epf_group(group);
+	list_del(&driver->epf_group);
+	mutex_unlock(&pci_epf_mutex);
+}
+
 /**
  * pci_epf_unregister_driver() - unregister the PCI EPF driver
  * @driver: the PCI EPF driver that has to be unregistered
@@ -145,16 +159,37 @@ EXPORT_SYMBOL_GPL(pci_epf_alloc_space);
  */
 void pci_epf_unregister_driver(struct pci_epf_driver *driver)
 {
-	struct config_group *group, *tmp;
+	pci_epf_remove_cfs(driver);
+	driver_unregister(&driver->driver);
+}
+EXPORT_SYMBOL_GPL(pci_epf_unregister_driver);
+
+static int pci_epf_add_cfs(struct pci_epf_driver *driver)
+{
+	struct config_group *group;
+	const struct pci_epf_device_id *id;
+
+	if (!IS_ENABLED(CONFIG_PCI_ENDPOINT_CONFIGFS))
+		return 0;
+
+	INIT_LIST_HEAD(&driver->epf_group);
+
+	id = driver->id_table;
+	while (id->name[0]) {
+		group = pci_ep_cfs_add_epf_group(id->name);
+		if (IS_ERR(group)) {
+			pci_epf_remove_cfs(driver);
+			return PTR_ERR(group);
+		}
 
 		mutex_lock(&pci_epf_mutex);
-	list_for_each_entry_safe(group, tmp, &driver->epf_group, group_entry)
-		pci_ep_cfs_remove_epf_group(group);
-	list_del(&driver->epf_group);
+		list_add_tail(&group->group_entry, &driver->epf_group);
 		mutex_unlock(&pci_epf_mutex);
-	driver_unregister(&driver->driver);
+		id++;
+	}
+
+	return 0;
 }
-EXPORT_SYMBOL_GPL(pci_epf_unregister_driver);
 
 /**
  * __pci_epf_register_driver() - register a new PCI EPF driver
@@ -167,8 +202,6 @@ int __pci_epf_register_driver(struct pci_epf_driver *driver,
 			      struct module *owner)
 {
 	int ret;
-	struct config_group *group;
-	const struct pci_epf_device_id *id;
 
 	if (!driver->ops)
 		return -EINVAL;
@@ -183,16 +216,7 @@ int __pci_epf_register_driver(struct pci_epf_driver *driver,
 	if (ret)
 		return ret;
 
-	INIT_LIST_HEAD(&driver->epf_group);
-
-	id = driver->id_table;
-	while (id->name[0]) {
-		group = pci_ep_cfs_add_epf_group(id->name);
-		mutex_lock(&pci_epf_mutex);
-		list_add_tail(&group->group_entry, &driver->epf_group);
-		mutex_unlock(&pci_epf_mutex);
-		id++;
-	}
+	pci_epf_add_cfs(driver);
 
 	return 0;
 }