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=-0.8 required=3.0 tests=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 34E99C433E1 for ; Mon, 18 May 2020 16:35:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1D7E020758 for ; Mon, 18 May 2020 16:35:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728231AbgERQfZ (ORCPT ); Mon, 18 May 2020 12:35:25 -0400 Received: from mga04.intel.com ([192.55.52.120]:42489 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727006AbgERQfZ (ORCPT ); Mon, 18 May 2020 12:35:25 -0400 IronPort-SDR: KvElP5/2Y7fTqu6FoVpLkWWMKzv155dsgLkDqyBd+64stnJCSJUASKVMKbarWal+DJ48hSuGIk a993Qs2DqCAw== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2020 09:35:25 -0700 IronPort-SDR: Qj+WXnA/CMDKXyowwwN+TrZetsAKeFYv7fSU5HWhoEvvxAtdWiX7hFyI6kx6ruaLQ1/tRW2ve8 xe+TfSNshqKg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,407,1583222400"; d="scan'208";a="465640555" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga005.fm.intel.com with ESMTP; 18 May 2020 09:35:20 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jaija-007T56-Mt; Mon, 18 May 2020 19:35:22 +0300 Date: Mon, 18 May 2020 19:35:22 +0300 From: Andy Shevchenko To: Maarten Brock Cc: Lukas Wunner , Heiko Stuebner , gregkh@linuxfoundation.org, jslaby@suse.com, matwey.kornilov@gmail.com, giulio.benetti@micronovasrl.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, christoph.muellner@theobroma-systems.com, Heiko Stuebner , linux-serial-owner@vger.kernel.org Subject: Re: [PATCH v3 3/5] serial: 8250: Support separate rs485 rx-enable GPIO Message-ID: <20200518163522.GK1634618@smile.fi.intel.com> References: <20200517215610.2131618-1-heiko@sntech.de> <20200517215610.2131618-4-heiko@sntech.de> <20200518151241.GG1634618@smile.fi.intel.com> <20200518152247.slenjeiiplps7mcd@wunner.de> <33547f6a596df2ca2ee8e647111e5fa1@vanmierlo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33547f6a596df2ca2ee8e647111e5fa1@vanmierlo.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 18, 2020 at 06:13:16PM +0200, Maarten Brock wrote: > On 2020-05-18 17:22, Lukas Wunner wrote: > > On Mon, May 18, 2020 at 06:12:41PM +0300, Andy Shevchenko wrote: > > > On Sun, May 17, 2020 at 11:56:08PM +0200, Heiko Stuebner wrote: > > > > From: Heiko Stuebner > > > > > > > > The RE signal is used to control the duplex mode of transmissions, > > > > aka receiving data while sending in full duplex mode, while stopping > > > > receiving data in half-duplex mode. > > > > > > > > On a number of boards the !RE signal is tied to ground so reception > > > > is always enabled except if the UART allows disabling the receiver. > > > > This can be taken advantage of to implement half-duplex mode - like > > > > done on 8250_bcm2835aux. > > > > > > > > Another solution is to tie !RE to RTS always forcing half-duplex mode. > > > > > > > > And finally there is the option to control the RE signal separately, > > > > like done here by introducing a new rs485-specific gpio that can be > > > > set depending on the RX_DURING_TX setting in the common em485 callbacks. > > > > > > ... > > > > > > > + port->rs485_re_gpio = devm_gpiod_get_optional(dev, "rs485-rx-enable", > > > > + GPIOD_OUT_HIGH); > > > > > > While reviewing some other patch I realized that people are missing > > > the > > > point of these GPIO flags when pin is declared to be output. > > > > > > HIGH here means "asserted" (consider active-high vs. active-low in > > > general). Is that the intention here? > > > > > > Lukas, same question to your patch. > > > > Yes. "High", i.e. asserted, means "termination enabled" in the case of > > my patch and "receiver enabled" in the case of Heiko's patch. > > But "High" on a gpio would disable the receiver when connected to !RE. No, that's exactly the point of the terminology (asserted means active whatever polarity it is). You need to define active-low in GPIO description. -- With Best Regards, Andy Shevchenko