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 30570C433FE for ; Sun, 6 Mar 2022 19:40:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234150AbiCFTlA (ORCPT ); Sun, 6 Mar 2022 14:41:00 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37846 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229737AbiCFTk5 (ORCPT ); Sun, 6 Mar 2022 14:40:57 -0500 Received: from bmailout3.hostsharing.net (bmailout3.hostsharing.net [IPv6:2a01:4f8:150:2161:1:b009:f23e:0]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CB2921E38; Sun, 6 Mar 2022 11:40:04 -0800 (PST) Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS DV RSA Mixed SHA256 2020 CA-1" (verified OK)) by bmailout3.hostsharing.net (Postfix) with ESMTPS id B3C27100D9417; Sun, 6 Mar 2022 20:40:02 +0100 (CET) Received: by h08.hostsharing.net (Postfix, from userid 100393) id F33A644C28B; Sun, 6 Mar 2022 20:40:01 +0100 (CET) Date: Sun, 6 Mar 2022 20:40:01 +0100 From: Lukas Wunner To: Ilpo =?iso-8859-1?Q?J=E4rvinen?= Cc: linux-serial@vger.kernel.org, Jiri Slaby , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Johan Hovold , Andy Shevchenko , 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: <20220306194001.GD19394@wunner.de> References: <20220302095606.14818-1-ilpo.jarvinen@linux.intel.com> <20220302095606.14818-7-ilpo.jarvinen@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20220302095606.14818-7-ilpo.jarvinen@linux.intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 02, 2022 at 11:56:05AM +0200, Ilpo Järvinen wrote: > This patch adds generic support for serial multipoint > addressing. Two new ioctls are added. TIOCSADDR is used to Nit: "This patch adds..." is superfluous. Just write "Add ..." in imperative mood. > 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. > [*] Technically, RS485 is just an electronic spec and does not > itself specify the 9th bit addressing mode but 9th bit seems > at least "semi-standard" way to do addressing with RS485. Is 9th bit addressing actually used by an Intel customer or was it implemented just for feature completeness? I think this mode isn't used often (I've never seen a use case myself), primarily because it requires disabling parity. Thanks, Lukas