From patchwork Fri May 27 22:27:08 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Mychaela N. Falconia" X-Patchwork-Id: 577043 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 70057C433F5 for ; Fri, 27 May 2022 22:36:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354143AbiE0Wgo (ORCPT ); Fri, 27 May 2022 18:36:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55124 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229996AbiE0Wgn (ORCPT ); Fri, 27 May 2022 18:36:43 -0400 Received: from freecalypso.org (freecalypso.org [195.154.163.71]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 52CFE2408A; Fri, 27 May 2022 15:36:42 -0700 (PDT) Received: by freecalypso.org (Postfix, from userid 1001) id 1AC8837401F1; Fri, 27 May 2022 22:27:09 +0000 (UTC) From: "Mychaela N. Falconia" To: Johan Hovold , Greg Kroah-Hartman , Jiri Slaby Cc: linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, mychaela.falconia@gmail.com Subject: [PATCH 1/6] tty: add port flag to suppress raising DTR & RTS on open Message-Id: <20220527222709.1AC8837401F1@freecalypso.org> Date: Fri, 27 May 2022 22:27:08 +0000 (UTC) Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org There exist special serial devices (either attaching to generic serial ports or containing a built-in USB-serial chip) in which DTR and/or RTS have been repurposed for non-standard uses. Depending on exactly how these signals are repurposed, standard POSIX/SUS behaviour of unconditionally raising both signals on open may range from harmless to undesirable to a total killer, precluding the use of Linux with such custom hardware. The newly added TTY_PORT_MANUAL_RTSDTR flag switches an individual serial port from POSIX/SUS standard to non-standard behaviour: when set, it suppresses the built-in action of raising DTR & RTS on serial port open. This flag can be exported through sysfs, and it can also be set by USB-serial device drivers when they see a custom hw device (identified by VID:PID) that is known to be wired in a way that requires this flag to be set. Co-developed-by: Johan Hovold Signed-off-by: Johan Hovold Signed-off-by: Mychaela N. Falconia --- drivers/tty/tty_port.c | 2 +- include/linux/tty_port.h | 11 +++++++++++ 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 880608a65773..59f1c49bb23c 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -441,7 +441,7 @@ EXPORT_SYMBOL(tty_port_carrier_raised); */ void tty_port_raise_dtr_rts(struct tty_port *port) { - if (port->ops->dtr_rts) + if (port->ops->dtr_rts && !tty_port_manual_rtsdtr(port)) port->ops->dtr_rts(port, 1); } EXPORT_SYMBOL(tty_port_raise_dtr_rts); diff --git a/include/linux/tty_port.h b/include/linux/tty_port.h index 58e9619116b7..9e5ad46d8a53 100644 --- a/include/linux/tty_port.h +++ b/include/linux/tty_port.h @@ -133,6 +133,7 @@ struct tty_port { #define TTY_PORT_CHECK_CD 4 /* carrier detect enabled */ #define TTY_PORT_KOPENED 5 /* device exclusively opened by kernel */ +#define TTY_PORT_MANUAL_RTSDTR 6 /* do not raise DTR & RTS on open */ void tty_port_init(struct tty_port *port); void tty_port_link_device(struct tty_port *port, struct tty_driver *driver, @@ -226,6 +227,16 @@ static inline void tty_port_set_kopened(struct tty_port *port, bool val) assign_bit(TTY_PORT_KOPENED, &port->iflags, val); } +static inline bool tty_port_manual_rtsdtr(const struct tty_port *port) +{ + return test_bit(TTY_PORT_MANUAL_RTSDTR, &port->iflags); +} + +static inline void tty_port_set_manual_rtsdtr(struct tty_port *port, bool val) +{ + assign_bit(TTY_PORT_MANUAL_RTSDTR, &port->iflags, val); +} + struct tty_struct *tty_port_tty_get(struct tty_port *port); void tty_port_tty_set(struct tty_port *port, struct tty_struct *tty); int tty_port_carrier_raised(struct tty_port *port);