From mboxrd@z Thu Jan 1 00:00:00 1970 From: Einar Vading Subject: Re: serial: imx: half-duplex RS485 operation with RTS active low Date: Mon, 16 Apr 2018 11:54:36 +0200 Message-ID: <20180416095436.7mxh4cqdvlyleryr@lnxeinarv.se.axis.com> References: <0e88706a05a302201be396d2f03c3e9e@agner.ch> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <0e88706a05a302201be396d2f03c3e9e@agner.ch> 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: Stefan Agner 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 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. > > 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); f_debug("Calling ioctl..."); if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) { f_critical("ioctl serial_rs485 failed"); return -1; } Hope it helps. > > 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 From mboxrd@z Thu Jan 1 00:00:00 1970 From: einar.vading@axis.com (Einar Vading) Date: Mon, 16 Apr 2018 11:54:36 +0200 Subject: serial: imx: half-duplex RS485 operation with RTS active low In-Reply-To: <0e88706a05a302201be396d2f03c3e9e@agner.ch> References: <0e88706a05a302201be396d2f03c3e9e@agner.ch> Message-ID: <20180416095436.7mxh4cqdvlyleryr@lnxeinarv.se.axis.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. > > 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); f_debug("Calling ioctl..."); if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) { f_critical("ioctl serial_rs485 failed"); return -1; } Hope it helps. > > 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 at vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html