greybus: camera-gb: Implement camera module reference counting as subject.

In explanation:

The main idea for implementing reference counting is to not block exit
until any other modules are in use. Camera responsibility is to handle
properly any additional calls after camera exit and that what this
patch is doing:

1. Free camera module when reference count is zero.
2. After camera cleanup handle properly any additional ongoing
   transaction. Return error if connection is destroyed.
Signed-off-by: NEvgeniy Borisov <eborisov@mm-sol.com>
Reviewed-by: NGjorgji Rosikopulos <grosikopulos@mm-sol.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/camera.c

@@ -35,7 +35,9 @@ struct gb_camera_debugfs_buffer {
 
 /**
  * struct gb_camera - A Greybus Camera Device
- * @connection: the greybus connection for camera control
+ * @connection: the greybus connection for camera management
+ * @data_connection: the greybus connection for camera data
+ * @mutex: protects the connection field
  * @debugfs: debugfs entries for camera protocol operations testing
  * @module: Greybus camera module registered to HOST processor.
  */
@@ -43,6 +45,7 @@ struct gb_camera {
 	struct gb_bundle *bundle;
 	struct gb_connection *connection;
 	struct gb_connection *data_connection;
+	struct mutex mutex;
 
 	struct {
 		struct dentry *root;
@@ -163,15 +166,24 @@ static int gb_camera_set_power_mode(struct gb_camera *gcam, bool hs)
 static int gb_camera_capabilities(struct gb_camera *gcam,
 				  u8 *capabilities, size_t *size)
 {
-	struct gb_operation *op;
+	struct gb_operation *op = NULL;
 	int ret;
 
+	mutex_lock(&gcam->mutex);
+
+	if (!gcam->connection) {
+		ret = -EINVAL;
+		goto done;
+	}
+
 	op = gb_operation_create_flags(gcam->connection,
 				       GB_CAMERA_TYPE_CAPABILITIES, 0, *size,
 				       GB_OPERATION_FLAG_SHORT_RESPONSE,
 				       GFP_KERNEL);
-	if (!op)
-		return -ENOMEM;
+	if (!op) {
+		ret = -ENOMEM;
+		goto done;
+	}
 
 	ret = gb_operation_request_send_sync(op);
 	if (ret) {
@@ -183,7 +195,9 @@ static int gb_camera_capabilities(struct gb_camera *gcam,
 	*size = op->response->payload_size;
 
 done:
-	gb_operation_put(op);
+	mutex_unlock(&gcam->mutex);
+	if (op)
+		gb_operation_put(op);
 	return ret;
 }
 
@@ -222,8 +236,9 @@ static int gb_camera_configure_streams(struct gb_camera *gcam,
 	req = kmalloc(req_size, GFP_KERNEL);
 	resp = kmalloc(resp_size, GFP_KERNEL);
 	if (!req || !resp) {
-		ret = -ENOMEM;
-		goto done;
+		kfree(req);
+		kfree(resp);
+		return -ENOMEM;
 	}
 
 	req->num_streams = nstreams;
@@ -239,6 +254,13 @@ static int gb_camera_configure_streams(struct gb_camera *gcam,
 		cfg->padding = 0;
 	}
 
+	mutex_lock(&gcam->mutex);
+
+	if (!gcam->connection) {
+		ret = -EINVAL;
+		goto done;
+	}
+
 	ret = gb_operation_sync(gcam->connection,
 				GB_CAMERA_TYPE_CONFIGURE_STREAMS,
 				req, req_size, resp, resp_size);
@@ -329,6 +351,7 @@ static int gb_camera_configure_streams(struct gb_camera *gcam,
 	ret = 0;
 
 done:
+	mutex_unlock(&gcam->mutex);
 	kfree(req);
 	kfree(resp);
 	return ret;
@@ -356,8 +379,17 @@ static int gb_camera_capture(struct gb_camera *gcam, u32 request_id,
 	req->num_frames = cpu_to_le16(num_frames);
 	memcpy(req->settings, settings, settings_size);
 
+	mutex_lock(&gcam->mutex);
+
+	if (!gcam->connection) {
+		ret = -EINVAL;
+		goto done;
+	}
+
 	ret = gb_operation_sync(gcam->connection, GB_CAMERA_TYPE_CAPTURE,
-				 req, req_size, NULL, 0);
+				req, req_size, NULL, 0);
+done:
+	mutex_unlock(&gcam->mutex);
 
 	kfree(req);
 
@@ -369,15 +401,26 @@ static int gb_camera_flush(struct gb_camera *gcam, u32 *request_id)
 	struct gb_camera_flush_response resp;
 	int ret;
 
+	mutex_lock(&gcam->mutex);
+
+	if (!gcam->connection) {
+		ret = -EINVAL;
+		goto done;
+	}
+
 	ret = gb_operation_sync(gcam->connection, GB_CAMERA_TYPE_FLUSH, NULL, 0,
 				&resp, sizeof(resp));
+
 	if (ret < 0)
-		return ret;
+		goto done;
 
 	if (request_id)
 		*request_id = le32_to_cpu(resp.request_id);
 
-	return 0;
+done:
+	mutex_unlock(&gcam->mutex);
+
+	return ret;
 }
 
 static int gb_camera_request_handler(struct gb_operation *op)
@@ -527,18 +570,6 @@ static const struct gb_camera_ops gb_cam_ops = {
 	.flush = gb_camera_op_flush,
 };
 
-static int gb_camera_register_intf_ops(struct gb_camera *gcam)
-{
-	gcam->module.priv = gcam;
-	gcam->module.ops = &gb_cam_ops;
-	return gb_camera_register(&gcam->module);
-}
-
-static int gb_camera_unregister_intf_ops(struct gb_camera *gcam)
-{
-	return gb_camera_unregister(&gcam->module);
-}
-
 /* -----------------------------------------------------------------------------
  * DebugFS
  */
@@ -899,14 +930,23 @@ static void gb_camera_cleanup(struct gb_camera *gcam)
 	if (gcam->data_connection) {
 		gb_connection_disable(gcam->data_connection);
 		gb_connection_destroy(gcam->data_connection);
+		gcam->data_connection = NULL;
 	}
 
+	mutex_lock(&gcam->mutex);
 	if (gcam->connection) {
 		gb_connection_disable(gcam->connection);
 		gb_connection_destroy(gcam->connection);
+		gcam->connection = NULL;
 	}
+	mutex_unlock(&gcam->mutex);
+}
 
-	kfree(gcam);
+static void gb_camera_release_module(struct kref *ref)
+{
+	struct gb_camera_module *cam_mod =
+		container_of(ref, struct gb_camera_module, refcount);
+	kfree(cam_mod->priv);
 }
 
 static int gb_camera_probe(struct gb_bundle *bundle,
@@ -964,6 +1004,8 @@ static int gb_camera_probe(struct gb_bundle *bundle,
 	if (ret)
 		goto error;
 
+	mutex_init(&gcam->mutex);
+
 	/*
 	 * Create the data connection between the camera module data CPort and
 	 * APB CDSI1. The CDSI1 CPort ID is hardcoded by the ES2 bridge.
@@ -986,7 +1028,11 @@ static int gb_camera_probe(struct gb_bundle *bundle,
 	if (ret < 0)
 		goto error;
 
-	ret = gb_camera_register_intf_ops(gcam);
+	gcam->module.priv = gcam;
+	gcam->module.ops = &gb_cam_ops;
+	gcam->module.interface_id = gcam->connection->intf->interface_id;
+	gcam->module.release = gb_camera_release_module;
+	ret = gb_camera_register(&gcam->module);
 	if (ret < 0)
 		goto error;
 
@@ -996,6 +1042,7 @@ static int gb_camera_probe(struct gb_bundle *bundle,
 
 error:
 	gb_camera_cleanup(gcam);
+	kfree(gcam);
 	return ret;
 }
 
@@ -1003,8 +1050,8 @@ static void gb_camera_disconnect(struct gb_bundle *bundle)
 {
 	struct gb_camera *gcam = greybus_get_drvdata(bundle);
 
-	gb_camera_unregister_intf_ops(gcam);
 	gb_camera_cleanup(gcam);
+	gb_camera_unregister(&gcam->module);
 }
 
 static const struct greybus_bundle_id gb_camera_id_table[] = {