On 16.04.2018 11:22, Uwe Kleine-König wrote: > 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? > Yes, sorry about that. But I think it is i.MX UART specific, I noticed the same behavior on i.MX 7 too. >> 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? > I use native RTS capability (which is in DTE mode the CTS signal...) >> 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). Just FYI, the fluke looks like a proper assert, but it is really only 50ns wide. >> >> 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. I used v4.17-rc1. I noticed your changes, but I it seems they make no difference, last week I noticed the same issue in v4.16. Do those customer boards use DTE mode? -- Stefan > >> Also, isn't enabling RX even in half-duplex mode quite common in order >> to detect collisions? > > I don't know. > Probably also depends on the exact use case and the transceiver configuration. -- Stefan -- 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
