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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 058D2C433EF for ; Thu, 10 Mar 2022 14:11:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237404AbiCJOMG (ORCPT ); Thu, 10 Mar 2022 09:12:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50890 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242756AbiCJOLZ (ORCPT ); Thu, 10 Mar 2022 09:11:25 -0500 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 730F2137012; Thu, 10 Mar 2022 06:10:23 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1646921423; x=1678457423; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=Vi9TQW28iAGVT+9VTJCeUAtR3L2XgA27dHLozP1I8zM=; b=G27wyBmWvNEAVSPYPdfrwrw+qFtSOgN9J0kMPS6K/D+VmhuYIzqR1hbC p9bJdKmSO6uC8JCtOBta+bjGdVF+yIluIHkAi1VYR23x6XUKsLfIbWQUx 8vbvo20B+2ak6a7Uav7VcfPjbUHU7Jc+Bb66v0a6QDuuCXDHyGikMH9UW Fczl5/I3uDFul2r3tp176PE3A3q63e/J7OzLrDmd6TuLLSycxbCud80oQ 9I2bOGvifIglHMBsvwzyESSnITNeg8Uar+8S8KZUbKv6h/BKsix/9ianu 0lA3j+sZ1VoUOkGAmoQ/FC3BmimF5cRcludSbtHSMJ0k3JwbGK35jpcQH g==; X-IronPort-AV: E=McAfee;i="6200,9189,10281"; a="279993773" X-IronPort-AV: E=Sophos;i="5.90,170,1643702400"; d="scan'208";a="279993773" Received: from fmsmga002.fm.intel.com ([10.253.24.26]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Mar 2022 06:10:23 -0800 X-IronPort-AV: E=Sophos;i="5.90,170,1643702400"; d="scan'208";a="642568750" Received: from smile.fi.intel.com ([10.237.72.59]) by fmsmga002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Mar 2022 06:10:15 -0800 Received: from andy by smile.fi.intel.com with local (Exim 4.95) (envelope-from ) id 1nSJTv-00EjUS-6x; Thu, 10 Mar 2022 16:09:31 +0200 Date: Thu, 10 Mar 2022 16:09:30 +0200 From: Andy Shevchenko To: Lukas Wunner Cc: Ilpo =?iso-8859-1?Q?J=E4rvinen?= , linux-serial , Jiri Slaby , Greg Kroah-Hartman , LKML , Johan Hovold , Heikki Krogerus , linux-api@vger.kernel.org, Richard Henderson , Ivan Kokshaysky , Matt Turner , linux-alpha@vger.kernel.org, Thomas Bogendoerfer , linux-mips@vger.kernel.org, "James E.J. Bottomley" , Helge Deller , linux-parisc@vger.kernel.org, Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , linuxppc-dev@lists.ozlabs.org, Yoshinori Sato , Rich Felker , linux-sh@vger.kernel.org, "David S. Miller" , sparclinux@vger.kernel.org, Chris Zankel , Max Filippov , linux-xtensa@linux-xtensa.org, Arnd Bergmann , linux-arch@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [RFC PATCH 6/7] serial: General support for multipoint addresses Message-ID: References: <20220302095606.14818-1-ilpo.jarvinen@linux.intel.com> <20220302095606.14818-7-ilpo.jarvinen@linux.intel.com> <20220306194001.GD19394@wunner.de> <20220309190521.GA9832@wunner.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220309190521.GA9832@wunner.de> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 09, 2022 at 08:05:21PM +0100, Lukas Wunner wrote: > On Mon, Mar 07, 2022 at 11:48:01AM +0200, Ilpo Järvinen wrote: > > On Sun, 6 Mar 2022, Lukas Wunner wrote: > > > On Wed, Mar 02, 2022 at 11:56:05AM +0200, Ilpo Järvinen wrote: > > > > This change is necessary for supporting devices with RS485 > > > > multipoint addressing [*]. > > > > > > If this is only used with RS485, why can't we just store the > > > addresses in struct serial_rs485 and use the existing TIOCSRS485 > > > and TIOCGRS485 ioctls? There's 20 bytes of padding left in > > > struct serial_rs485 which you could use. No need to add more > > > user-space ABI. > > > > It could if it is agreed that serial multipoint addressing is just > > a thing in RS-485 and nowhere else? In that case, there is no point > > in adding more generic support for it. > > It's just that the above-quoted sentence in the commit message > specifically mentions RS485. If you intend to use it with RS232 > as well, that should be made explicit, otherwise one wonders why > it wasn't integrated into struct serial_rs485. > > I have no idea how common 9th bit addressing mode is with RS232. > Goggle turns up links saying it's mainly used with RS485, "but also > RS232". Since RS232 isn't a bus but a point-to-point link, > 9th bit addressing doesn't seem to make as much sense. In my student years I have an exercise to use 9-bit addressing mode on RS232. Obviously I forgot all of the details, but I remember that that has a practical application. -- With Best Regards, Andy Shevchenko