On Mon, Apr 16, 2018 at 03:01:44PM +0200, Stefan Agner wrote: > On 16.04.2018 12:29, Stefan Agner wrote: > > 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. > > > > Also tried DCE mode, the same behavior. > > Two screenshots showing TX/RTS (CTS_B) in different settings: > https://imgur.com/a/PbUex > > The little fluke disappears when disabling RX before setting CTSC: > > --- a/drivers/tty/serial/imx.c > +++ b/drivers/tty/serial/imx.c > @@ -657,6 +657,9 @@ static void imx_uart_start_tx(struct uart_port > *port) > if (port->rs485.flags & SER_RS485_ENABLED) { > u32 ucr2; > > + if (!(port->rs485.flags & SER_RS485_RX_DURING_TX)) > + imx_uart_stop_rx(port); > + > ucr2 = imx_uart_readl(sport, UCR2); > if (port->rs485.flags & SER_RS485_RTS_ON_SEND) > imx_uart_rts_active(sport, &ucr2); > @@ -664,9 +667,6 @@ static void imx_uart_start_tx(struct uart_port > *port) > imx_uart_rts_inactive(sport, &ucr2); > imx_uart_writel(sport, ucr2, UCR2); > > - if (!(port->rs485.flags & SER_RS485_RX_DURING_TX)) > - imx_uart_stop_rx(port); > - > /* > * Enable transmitter and shifter empty irq only if DMA > is off. > * In the DMA case this is done in the tx-callback. > > It seems that if the RX path is disabled, CTS_B is no longer > controllable. It just stays high. That is not a problem in the high > active RTS case... However, it breaks low active half-duplex... > > It seems that this thread is describing this situation: > https://community.nxp.com/thread/385047 So better use a gpio instead of the hardware-function? Adding a respective check in the driver would be nice though. 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
