From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Agner Subject: Re: serial: imx: half-duplex RS485 operation with RTS active low Date: Mon, 16 Apr 2018 12:35:24 +0200 Message-ID: <775db0158e310ebb17c6143a5b8ff4cd@agner.ch> References: <0e88706a05a302201be396d2f03c3e9e@agner.ch> <20180416095436.7mxh4cqdvlyleryr@lnxeinarv.se.axis.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180416095436.7mxh4cqdvlyleryr@lnxeinarv.se.axis.com> 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: Einar Vading Cc: linux-arm-kernel@lists.infradead.org, s.hauer@pengutronix.de, baruch@tkos.co.il, linux-serial@vger.kernel.org, u.kleine-koenig@pengutronix.de List-Id: linux-serial@vger.kernel.org On 16.04.2018 11:54, Einar Vading wrote: > On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote: >> 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 where struggling a bit with half duplex rs485 too a while ago. >> >> 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). > > I think this is what we had too. But if I recall we where supposed to be > active-high but I think the behavior is the same either way. With v4.17-rc1, active high RTS, DTE in half duplex mode seems to work fine (looks good on an oscilloscope). However, active low seems to be broken. >> >> 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... > > We have a (RTS active high) configuration working for us now with only > > uart-has-rtscts > > in DT, and then when using the port we do > > struct serial_rs485 rs485conf; > memset(&rs485conf, 0x00, sizeof(struct serial_rs485)); > > rs485conf.flags |= SER_RS485_ENABLED; > rs485conf.flags |= SER_RS485_RTS_ON_SEND; > rs485conf.flags &= ~(SER_RS485_RTS_AFTER_SEND); >>From what I can tell, in v4.17-rc1 this should be equivalent to just: linux,rs485-enabled-at-boot-time; > > f_debug("Calling ioctl..."); > if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) { > f_critical("ioctl serial_rs485 failed"); > return -1; > } > > Hope it helps. Thanks, I will check using RS485 flags via ioctrl. -- Stefan >> >> 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 > > // Einar >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-serial" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html