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=-16.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 ED23DC432BE for ; Thu, 5 Aug 2021 05:52:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C22CC60EBB for ; Thu, 5 Aug 2021 05:52:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234675AbhHEFwX (ORCPT ); Thu, 5 Aug 2021 01:52:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:41108 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229892AbhHEFwU (ORCPT ); Thu, 5 Aug 2021 01:52:20 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5970760EBB; Thu, 5 Aug 2021 05:52:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1628142726; bh=ZKU+PLv7kgX0N+MxB8BCiFigoXZVFNf9axw628nM5to=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=paTwXLBvTHtUmdQ4JprqZteMH/wu2+6VdbxtSgIOozVFGbFvzqjsvbsJT5SSHWCAN Gz5r8daBRPxitkfZxcJmPPVc9k4gCT5Y+y/G7HknBgTpJH0pe1nX6pec/LB2rjvXZu W/ENmS3ueNRHdSdvUg49Fq9fv+l+dTv7kBvc2Ims= Date: Thu, 5 Aug 2021 07:52:03 +0200 From: Greg Kroah-Hartman To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Marek =?iso-8859-1?Q?Beh=FAn?= , libc-alpha@sourceware.org, "G. Branden Robinson" , linux-man@vger.kernel.org, linux-serial@vger.kernel.org, Alejandro Colomar , Michael Kerrisk Subject: Re: [PATCH v3] ioctl_tty.2: Add example how to get or set baudrate on the serial port Message-ID: References: <20210730095333.6118-1-pali@kernel.org> <20210801135146.14849-1-pali@kernel.org> <20210804220808.cetleob6dldpfnjk@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210804220808.cetleob6dldpfnjk@pali> Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org On Thu, Aug 05, 2021 at 12:08:08AM +0200, Pali Rohár wrote: > + linux-serial > + Greg > > Greg, could I ask you for reviewing this documentation manpage patch? If it is submitted in a format I can review, sure (i.e. not top-post...) But I will dig down below to say one thing... > > On Sunday 01 August 2021 15:51:45 Pali Rohár wrote: > > Signed-off-by: Pali Rohár > > > > --- > > Changes in v3: > > * Check support for custom baudrate only based on BOTHER macro > > * Use TCGETS/TCSETS/termios when TCGETS2/TCSETS2/termios2 is not available > > > > Changes in v2: > > * Use \e for backslash > > * Use exit(EXIT_*) instead of return num > > * Sort includes > > * Add comment about possible fallback > > --- > > > > Hello Alejandro! > > > > I found out that this stuff is more complicated as I originally thought. > > And seems that additional documentation on this topic is needed... > > > > For setting custom baudrate it is needed to set BOTHER flag in c_cflag > > field and baudrate value itself in c_ospeed and c_ispeed fields. > > > > So when BOTHER flag is not provided by then setting custom > > baudrate is not possible, fields c_ospeed and c_ispeed do not exist (and > > only some predefined Bnnn baudrate values are supported). This applies when > > compiling application with older version of header files (prior support for > > custom baudrate was introduced into header files). > > > > First caveat: BOTHER constant is different for different architectures. > > So it is not possible to provide fallback #ifndef..#define BOTHER. > > > > And now the biggest issue: Some architectures have these c_ospeed and > > c_ispeed fields in struct termios and some in struct termios2. > > > > TCGETS/TCSETS ioctls use struct termios and TCGETS/TCSETS2 use > > struct termios2. > > > > Some architectures (e.g. amd64) provide both struct termios and struct > > termios2, but c_ospeed and c_ispeed are only in struct termios2. > > > > Some other architectures (e.g. alpha) provide both struct termios and struct > > termios2 and both have c_ospeed and c_ispeed fields. > > > > And some other architectures (e.g. powerpc) provide only struct termios > > (no struct termios2) and it has c_ospeed and c_ispeed fields. > > > > So basically to support all architectures it is needed to use > > struct termios2 when TCGETS2/TCSETS2 is supported. Otherwise it is needed > > to use struct termios with TCGETS/TCSETS (case for e.g. powerpc). > > > > I updated v3 patch to handle this logic. > > --- > > man2/ioctl_tty.2 | 73 ++++++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 73 insertions(+) > > > > diff --git a/man2/ioctl_tty.2 b/man2/ioctl_tty.2 > > index 3020f9984872..d83cbd17225b 100644 > > --- a/man2/ioctl_tty.2 > > +++ b/man2/ioctl_tty.2 > > @@ -764,6 +764,79 @@ main(void) > > close(fd); > > } > > .EE > > +.PP > > +Get or set arbitrary baudrate on the serial port. > > +.PP > > +.EX > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > +#include > > + > > +int > > +main(int argc, char *argv[]) > > +{ > > +#ifndef BOTHER > > + fprintf(stderr, "BOTHER is unsupported\en"); > > + /* Program may fallback to TCGETS/TCSETS with Bnnn constants */ > > + exit(EXIT_FAILURE); So this is a BOTHER test only? What is the goal of this program? Don't throw a bunch of #ifdef in here for no good reason. These options should all be present on all normal kernels, why wouldn't they be? thanks, greg k-h