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Received: from AM0PR04MB6467.eurprd04.prod.outlook.com (2603:10a6:208:16c::20) by DB9PR04MB9356.eurprd04.prod.outlook.com (2603:10a6:10:36a::9) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.7068.11; Thu, 30 Nov 2023 13:09:51 +0000 Received: from AM0PR04MB6467.eurprd04.prod.outlook.com ([fe80::5c46:ada1:fcf3:68e6]) by AM0PR04MB6467.eurprd04.prod.outlook.com ([fe80::5c46:ada1:fcf3:68e6%7]) with mapi id 15.20.7046.023; Thu, 30 Nov 2023 13:09:51 +0000 Message-ID: <7e649033-0e1d-4c21-a1f3-ceb2de894861@suse.com> Date: Thu, 30 Nov 2023 14:09:48 +0100 User-Agent: Mozilla Thunderbird Content-Language: en-US To: Johan Hovold Cc: Greg Kroah-Hartman , Jiri Slaby , USB list , linux-serial@vger.kernel.org From: Oliver Neukum Subject: question on correct error return from break_ctl() Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: FR4P281CA0386.DEUP281.PROD.OUTLOOK.COM (2603:10a6:d10:f7::14) To AM0PR04MB6467.eurprd04.prod.outlook.com (2603:10a6:208:16c::20) Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: AM0PR04MB6467:EE_|DB9PR04MB9356:EE_ X-MS-Office365-Filtering-Correlation-Id: 5f862ec5-fa9d-413c-6260-08dbf1a5a2f7 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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The tty layer in drivers/tty/tty_io.c::send_break() static int send_break(struct tty_struct *tty, unsigned int duration) { int retval; if (tty->ops->break_ctl == NULL) return 0; not supporting break_ctl() is treated as the operation succeeding. Yet in drivers/usb/serial/usb-serial.c::serial_break() static int serial_break(struct tty_struct *tty, int break_state) { struct usb_serial_port *port = tty->driver_data; dev_dbg(&port->dev, "%s\n", __func__); if (port->serial->type->break_ctl) return port->serial->type->break_ctl(tty, break_state); return -ENOTTY; } we are seeing that not supporting break_ctl() leads to returning -ENOTTY, which drivers/tty/tty_io.c::send_break() will return to user space. These reactions are at odds with each other. What is a driver supposed to do? Regards Oliver