serial: imx: half-duplex RS485 operation with RTS active low

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

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 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).

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...?

Also, isn't enabling RX even in half-duplex mode quite common in order
to detect collisions?

--
Stefan

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

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 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).

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...?

Also, isn't enabling RX even in half-duplex mode quite common in order
to detect collisions?

--
Stefan

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

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/  |

serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

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-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

On 16.04.2018 11:22, Uwe Kleine-K?nig 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

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

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

--
Stefan

>>>
>>> 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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

On 16.04.2018 12:29, Stefan Agner wrote:
> On 16.04.2018 11:22, Uwe Kleine-K?nig 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

--
Stefan

>>>
>>> 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

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

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/  |

serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

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-K?nig 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-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

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

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

On 16.04.2018 15:42, Uwe Kleine-K?nig 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-K?nig 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

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

Hallo Stefan,

On Mon, Apr 16, 2018 at 06:12:41PM +0200, Stefan Agner wrote:
> On 16.04.2018 15:42, Uwe Kleine-König wrote:
> > 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...?

look at the code between the calls to uart_get_rs485_mode() and
imx_uart_rs485_config(). Something like that would be needed and
imx_uart_rs485_config must adapt the flags accordingly.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

serial: imx: half-duplex RS485 operation with RTS active low

[Uwe Kleine-König]

Hallo Stefan,

On Mon, Apr 16, 2018 at 06:12:41PM +0200, Stefan Agner wrote:
> On 16.04.2018 15:42, Uwe Kleine-K?nig wrote:
> > 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...?

look at the code between the calls to uart_get_rs485_mode() and
imx_uart_rs485_config(). Something like that would be needed and
imx_uart_rs485_config must adapt the flags accordingly.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-K?nig            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Einar Vading]

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

serial: imx: half-duplex RS485 operation with RTS active low

[Einar Vading]

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

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Einar Vading]

On Mon, Apr 16, 2018 at 11:54:36AM +0200, Einar Vading wrote:
> On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote:

Forgot to mention that we are not using DTE-de mode. We tried to but failed.

> > 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
// 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
> --
> 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

serial: imx: half-duplex RS485 operation with RTS active low

[Einar Vading]

On Mon, Apr 16, 2018 at 11:54:36AM +0200, Einar Vading wrote:
> On Mon, Apr 16, 2018 at 11:14:32AM +0200, Stefan Agner wrote:

Forgot to mention that we are not using DTE-de mode. We tried to but failed.

> > 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
// 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
> --
> 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

Re: serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

On 16.04.2018 11:54, Einar Vading wrote:
> 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.

With v4.17-rc1, active high RTS, DTE in half duplex mode seems to work
fine (looks good on an oscilloscope). However, active low seems to be
broken.

>>
>> 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);

>From what I can tell, in v4.17-rc1 this should be equivalent to just:

 	linux,rs485-enabled-at-boot-time;

> 
>     f_debug("Calling ioctl...");
>     if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
>       f_critical("ioctl serial_rs485 failed");
>       return -1;
>     }
> 
> Hope it helps.

Thanks, I will check using RS485 flags via ioctrl.

--
Stefan

>>
>> 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

serial: imx: half-duplex RS485 operation with RTS active low

[Stefan Agner]

On 16.04.2018 11:54, Einar Vading wrote:
> 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.

With v4.17-rc1, active high RTS, DTE in half duplex mode seems to work
fine (looks good on an oscilloscope). However, active low seems to be
broken.

>>
>> 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);

>From what I can tell, in v4.17-rc1 this should be equivalent to just:

 	linux,rs485-enabled-at-boot-time;

> 
>     f_debug("Calling ioctl...");
>     if (ioctl (fd, TIOCSRS485, &rs485conf) < 0) {
>       f_critical("ioctl serial_rs485 failed");
>       return -1;
>     }
> 
> Hope it helps.

Thanks, I will check using RS485 flags via ioctrl.

--
Stefan

>>
>> 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
>>
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