From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E6BBC433FE for ; Thu, 10 Dec 2020 10:43:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E35B123D98 for ; Thu, 10 Dec 2020 10:43:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728438AbgLJKm5 (ORCPT ); Thu, 10 Dec 2020 05:42:57 -0500 Received: from fieber.vanmierlo.com ([84.243.197.177]:37512 "EHLO kerio9.vanmierlo.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728865AbgLJKm5 (ORCPT ); Thu, 10 Dec 2020 05:42:57 -0500 X-Footer: dmFubWllcmxvLmNvbQ== Received: from roundcube.vanmierlo.com ([192.168.37.37]) (authenticated user m.brock@vanmierlo.com) by kerio9.vanmierlo.com (Kerio Connect 9.3.0 patch 1) with ESMTPA; Thu, 10 Dec 2020 11:41:24 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Thu, 10 Dec 2020 11:41:24 +0100 From: Maarten Brock To: Mychaela Falconia Cc: Greg Kroah-Hartman , Johan Hovold , Jiri Slaby , "Mychaela N . Falconia" , linux-serial@vger.kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/7] tty: add flag to suppress ready signalling on open In-Reply-To: References: <20201202113942.27024-1-johan@kernel.org> Message-ID: <6b81cca21561305b55ba8f019b78da28@vanmierlo.com> X-Sender: m.brock@vanmierlo.com User-Agent: Roundcube Webmail/1.3.3 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Hello Mychaela, On 2020-12-09 23:49, Mychaela Falconia wrote: > Greg K-H wrote: > >> I think we need more review for the rest of the series. This does >> change the way serial ports work in a non-traditional way (i.e. using >> sysfs instead of terminal settings). > > But the problem is that the current status quo is fundamentally broken > for those hardware devices in which DTR and/or RTS have been repurposed > for something other than modem and flow control. Right now whenever a > "cold" (never previously opened) serial port is opened for the first > time, that open action immediately and unstoppably asserts both DTR > and RTS hardware outputs, without giving userspace any opportunity to > say "no, please don't do it". Yes, this behaviour is codified in a > bunch of standards that ultimately trace back to 1970s Original UNIX, > but just because it is a standard does not make it right - this > Unix/POSIX/Linux "standard" serial port behaviour is a bug, not a > feature. I agree. And an application not configuring the required handshakes, but still relying on them is an equal bug. > But if there exist some custom hw devices out there that are in the > same predicament as my DUART28 adapter, but are different in that they > are classic old-fashioned RS-232 rather than integrated USB-serial, > with no place to assign a custom USB ID, *then* we need a non-USB-ID- > dependent solution such as Johan's sysfs attribute or O_DIRECT. Any device with a classic old-fashioned RS-232 has probably already solved this in another way or is accepted as not working on Linux. And then there is also the device tree (overlay?) through which a quirk like this can be communicated to the kernel driver. Not sure if this could help for a plug-and-play device like on USB. >> So I want to get a bunch of people >> to agree that this is ok to do things this way now before taking this >> new user-visible api. Personally, I would prefer the VID:PID to enforce the quirk and an O_DIRECT (or other) flag used on open() as general backup plan. To me a sysfs solution seems illogical. > If the concern is with the new sysfs interface or the proposed O_DIRECT > alternative, how about deferring those while allowing specific USB ID > support to go in first? Right now there already exists at least one > piece of hardware actively supported by its manufacturer (my gadget) > that has a custom USB ID and requires the quirk - what is wrong with > adding support for this existing specific hw? How about merging > Johan's patch that defines the NORDY flag in tty_port, merging the > ftdi_sio driver patch setting this flag for my custom USB ID, allowing > other hardware engineers in the same boat to submit similar quirk > patches for their affected custom hw with custom USB IDs, while > deferring the sysfs patches until there is a more pressing need for > quirky devices that have no custom USB IDs? > > Sincerely, > Mychaela Again, I agree. Maarten