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=-21.4 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,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 6F987C4320A for ; Thu, 5 Aug 2021 08:30:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3EE416105A for ; Thu, 5 Aug 2021 08:30:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238242AbhHEIae (ORCPT ); Thu, 5 Aug 2021 04:30:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:45264 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234796AbhHEIae (ORCPT ); Thu, 5 Aug 2021 04:30:34 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9B3E960F43; Thu, 5 Aug 2021 08:30:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1628152218; bh=zeb3qJUSxyPK9h0+JXsnecaNm4A/kQexp6o8pYdnCQw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=OLJ/GybJqQUIzF1wAIJ8b+WolEVEMv1l5vYwKShxIc7OrjhpqCrTiNN64ayvtxZ9O sXlzkJRqIhPq0fXjR7Yc0EIabpTbMf4NH3NcjKhntrFHHgM11CfwaTqDvX4xkga7kn 2HDS6w1M9l5hVytvPysIj9Bmslwysl+NbTCdjymQ= Date: Thu, 5 Aug 2021 10:30:15 +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> <20210805082243.qciylqnt5g74if7i@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210805082243.qciylqnt5g74if7i@pali> Precedence: bulk List-ID: X-Mailing-List: linux-man@vger.kernel.org On Thu, Aug 05, 2021 at 10:22:43AM +0200, Pali Rohár wrote: > On Thursday 05 August 2021 07:52:03 Greg Kroah-Hartman wrote: > > 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? > > Yes. > > > 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? > > I wanted to provide complete example which compiles fine on all Linux > systems, even with older include header files. I do not know right now > in which kernel version was introduced BOTHER support for all > architectures. We have all of the kernel source in a tool that would allow you to to determine this quite easily :) > If BOHTER is not supported then it is possible to still use Bnnn > constants to get / set baudrate. Just it is needed to write long code > for converting number to suitable Bnnn constant. > > Do you think that this BOTHER check is not useful in this case? I think you should provide an example of how to use BOTHER, yes, as it is hard to find good examples out there as they keep floating around. Here's one that I point people to a lot: https://github.com/GrantEdwards/Linux-arbitrary-baud Make the example code easy to follow. Also, you forgot a license for this code, that is required if you want people to use it... thanks, greg k-h