From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: serial: imx: half-duplex RS485 operation with RTS active low Date: Mon, 16 Apr 2018 11:14:32 +0200 Message-ID: <0e88706a05a302201be396d2f03c3e9e@agner.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: s.hauer@pengutronix.de, u.kleine-koenig@pengutronix.de, baruch@tkos.co.il Cc: linux-arm-kernel@lists.infradead.org, linux-serial@vger.kernel.org List-Id: linux-serial@vger.kernel.org Hi, Using upstream I noticed that RS-485 does not work in the default configuration for our platforms (Toradex Apalis/Colibri). Closer debugging shows that it is related to "serial: imx: default to half duplex rs485". We use the i.MX UART in DTE mode and control the RS-485 transceiver using the RTS signal in low-active mode. uart-has-rtscts; fsl,dte-mode; linux,rs485-enabled-at-boot-time; rs485-rts-active-low; Using this setting leads to the RTS signal not getting asserted (the oscilloscope only shows a very short fluke before the start bit is sent). However, using uart-has-rtscts; fsl,dte-mode; linux,rs485-enabled-at-boot-time; rs485-rts-active-low; rs485-rx-during-tx; Asserts the RTS signal low active just fine... Is this a known problem? Any idea where that could come from? It looks as if the receiver part is actually enabling RTS...? Also, isn't enabling RX even in half-duplex mode quite common in order to detect collisions? -- Stefan