devlink: Add API to register and unregister single parameter

Currently device configuration parameters can be registered as an array.
Due to this a constant array must be registered. A single driver
supporting multiple devices each with different device capabilities end
up registering all parameters even if it doesn't support it.

One possible workaround a driver can do is, it registers multiple single
entry arrays to overcome such limitation.

Better is to provide a API that enables driver to register/unregister a
single parameter. This also further helps in two ways.
(1) to reduce the memory of devlink_param_entry by avoiding in registering
parameters which are not supported by the device.
(2) avoid generating multiple parameter add, delete, publish, unpublish,
init value notifications for such unsupported parameters
Signed-off-by: Parav Pandit <parav@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/devlink.h

@@ -1645,6 +1645,10 @@ int devlink_params_register(struct devlink *devlink,
 void devlink_params_unregister(struct devlink *devlink,
 			       const struct devlink_param *params,
 			       size_t params_count);
+int devlink_param_register(struct devlink *devlink,
+			   const struct devlink_param *param);
+void devlink_param_unregister(struct devlink *devlink,
+			      const struct devlink_param *param);
 void devlink_params_publish(struct devlink *devlink);
 void devlink_params_unpublish(struct devlink *devlink);
 int devlink_port_params_register(struct devlink_port *devlink_port,

net/core/devlink.c

@@ -9903,6 +9903,43 @@ void devlink_params_unregister(struct devlink *devlink,
 }
 EXPORT_SYMBOL_GPL(devlink_params_unregister);
 
+/**
+ * devlink_param_register - register one configuration parameter
+ *
+ * @devlink: devlink
+ * @param: one configuration parameter
+ *
+ * Register the configuration parameter supported by the driver.
+ * Return: returns 0 on successful registration or error code otherwise.
+ */
+int devlink_param_register(struct devlink *devlink,
+			   const struct devlink_param *param)
+{
+	int err;
+
+	mutex_lock(&devlink->lock);
+	err = __devlink_param_register_one(devlink, 0, &devlink->param_list,
+					   param, DEVLINK_CMD_PARAM_NEW);
+	mutex_unlock(&devlink->lock);
+	return err;
+}
+EXPORT_SYMBOL_GPL(devlink_param_register);
+
+/**
+ * devlink_param_unregister - unregister one configuration parameter
+ * @devlink: devlink
+ * @param: configuration parameter to unregister
+ */
+void devlink_param_unregister(struct devlink *devlink,
+			      const struct devlink_param *param)
+{
+	mutex_lock(&devlink->lock);
+	devlink_param_unregister_one(devlink, 0, &devlink->param_list, param,
+				     DEVLINK_CMD_PARAM_DEL);
+	mutex_unlock(&devlink->lock);
+}
+EXPORT_SYMBOL_GPL(devlink_param_unregister);
+
 /**
  *	devlink_params_publish - publish configuration parameters
  *