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Thu, 19 Apr 2018 12:26:20 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:54389 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753920AbeDSQ0T (ORCPT ); Thu, 19 Apr 2018 12:26:19 -0400 Date: Thu, 19 Apr 2018 18:26:14 +0200 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Stefan Agner Cc: gregkh@linuxfoundation.org, lukas@wunner.de, jslaby@suse.com, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] serial: imx: warn user when using unsupported configuration Message-ID: <20180419162614.erf33d4kwt2clnev@pengutronix.de> References: <20180419153916.21898-1-stefan@agner.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20180419153916.21898-1-stefan@agner.ch> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c5 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-serial@vger.kernel.org Sender: linux-serial-owner@vger.kernel.org X-Mailing-List: linux-serial@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: Hello Stefan, On Thu, Apr 19, 2018 at 05:39:16PM +0200, Stefan Agner wrote: > When using half-duplex mode (which disables receiver during txing) > the RTS signal cannot be driven low during transmission when using > i.MX UART RTS/CTS control. This seems to be a limitation of the > i.MX UART IP: The RTS (CTS_B) signal is controlled by the receiver. > When the receiver is disabled, the signal stays in UART logic idle > state which is high... > > If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during > transmission. Since this is the default state of the RTS (CTS_B) > signal when the receiver is off, half-duplex mode in this > configuration works fine. > > However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set) > cannot be generated when the receiver is turned off. > > Print an error if the user selects this unsupported configuration > (both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and > configure the closest working configuration (set the > SER_RS485_RX_DURING_TX flag). > > Signed-off-by: Stefan Agner Acked-by: Uwe Kleine-König Thanks Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ |