On 16.04.2018 15:42, Uwe Kleine-König wrote: > 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? I guess so, did not test that though. Or use full duplex mode. That is what we used anyways in the past, even when using a single RS485 bus (half duplex) on the physical layer anyway. > > Adding a respective check in the driver would be nice though. Hm, yes agreed. Where would that check go? In probe? Then I guess it only would warn when using device tree properties...? -- 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
