Hi Stefan, On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote: > Using upstream I noticed that RS-485 does not work in the default > configuration for our platforms (Toradex Apalis/Colibri). Closer This is an i.MX6? > 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; That means you're not using a GPIO for RTS signaling, right? > 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...? Which kernel version do you use? My latest rs485 related patches went into v4.17-rc1. With that I managed to make rs485 half duplex work on several customer boards. > Also, isn't enabling RX even in half-duplex mode quite common in order > to detect collisions? I don't know. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
