* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 9:14 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 9:14 UTC (permalink / raw)
To: s.hauer, u.kleine-koenig, baruch; +Cc: linux-arm-kernel, linux-serial
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 9:14 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 9:14 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 9:14 ` Stefan Agner
@ 2018-04-16 9:22 ` Uwe Kleine-König
-1 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 9:22 UTC (permalink / raw)
To: Stefan Agner; +Cc: linux-arm-kernel, s.hauer, baruch, linux-serial
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 9:22 ` Uwe Kleine-König
0 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 9:22 UTC (permalink / raw)
To: linux-arm-kernel
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 9:14 ` Stefan Agner
@ 2018-04-16 9:54 ` Einar Vading
-1 siblings, 0 replies; 20+ messages in thread
From: Einar Vading @ 2018-04-16 9:54 UTC (permalink / raw)
To: Stefan Agner
Cc: linux-arm-kernel, s.hauer, baruch, linux-serial, u.kleine-koenig
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 9:54 ` Einar Vading
0 siblings, 0 replies; 20+ messages in thread
From: Einar Vading @ 2018-04-16 9:54 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 9:54 ` Einar Vading
@ 2018-04-16 9:57 ` Einar Vading
-1 siblings, 0 replies; 20+ messages in thread
From: Einar Vading @ 2018-04-16 9:57 UTC (permalink / raw)
To: Stefan Agner
Cc: linux-arm-kernel, s.hauer, baruch, linux-serial, u.kleine-koenig
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 9:57 ` Einar Vading
0 siblings, 0 replies; 20+ messages in thread
From: Einar Vading @ 2018-04-16 9:57 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 9:22 ` Uwe Kleine-König
@ 2018-04-16 10:29 ` Stefan Agner
-1 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 10:29 UTC (permalink / raw)
To: Uwe Kleine-König; +Cc: s.hauer, baruch, linux-arm-kernel, linux-serial
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 10:29 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 10:29 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 9:54 ` Einar Vading
@ 2018-04-16 10:35 ` Stefan Agner
-1 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 10:35 UTC (permalink / raw)
To: Einar Vading
Cc: linux-arm-kernel, s.hauer, baruch, linux-serial, u.kleine-koenig
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 10:35 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 10:35 UTC (permalink / raw)
To: linux-arm-kernel
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 at vger.kernel.org
>> More majordomo info at http://vger.kernel.org/majordomo-info.html
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 10:29 ` Stefan Agner
@ 2018-04-16 13:01 ` Stefan Agner
-1 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 13:01 UTC (permalink / raw)
To: Uwe Kleine-König; +Cc: s.hauer, baruch, linux-arm-kernel, linux-serial
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 13:01 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 13:01 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 13:01 ` Stefan Agner
@ 2018-04-16 13:42 ` Uwe Kleine-König
-1 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 13:42 UTC (permalink / raw)
To: Stefan Agner; +Cc: s.hauer, baruch, linux-arm-kernel, linux-serial
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 13:42 ` Uwe Kleine-König
0 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 13:42 UTC (permalink / raw)
To: linux-arm-kernel
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 13:42 ` Uwe Kleine-König
@ 2018-04-16 16:12 ` Stefan Agner
-1 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 16:12 UTC (permalink / raw)
To: Uwe Kleine-König; +Cc: s.hauer, baruch, linux-arm-kernel, linux-serial
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
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^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 16:12 ` Stefan Agner
0 siblings, 0 replies; 20+ messages in thread
From: Stefan Agner @ 2018-04-16 16:12 UTC (permalink / raw)
To: linux-arm-kernel
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
^ permalink raw reply [flat|nested] 20+ messages in thread
* Re: serial: imx: half-duplex RS485 operation with RTS active low
2018-04-16 16:12 ` Stefan Agner
@ 2018-04-16 18:02 ` Uwe Kleine-König
-1 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 18:02 UTC (permalink / raw)
To: Stefan Agner; +Cc: s.hauer, baruch, linux-arm-kernel, linux-serial
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
* serial: imx: half-duplex RS485 operation with RTS active low
@ 2018-04-16 18:02 ` Uwe Kleine-König
0 siblings, 0 replies; 20+ messages in thread
From: Uwe Kleine-König @ 2018-04-16 18:02 UTC (permalink / raw)
To: linux-arm-kernel
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/ |
^ permalink raw reply [flat|nested] 20+ messages in thread
end of thread, other threads:[~2018-04-16 18:02 UTC | newest]
Thread overview: 20+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-04-16 9:14 serial: imx: half-duplex RS485 operation with RTS active low Stefan Agner
2018-04-16 9:14 ` Stefan Agner
2018-04-16 9:22 ` Uwe Kleine-König
2018-04-16 9:22 ` Uwe Kleine-König
2018-04-16 10:29 ` Stefan Agner
2018-04-16 10:29 ` Stefan Agner
2018-04-16 13:01 ` Stefan Agner
2018-04-16 13:01 ` Stefan Agner
2018-04-16 13:42 ` Uwe Kleine-König
2018-04-16 13:42 ` Uwe Kleine-König
2018-04-16 16:12 ` Stefan Agner
2018-04-16 16:12 ` Stefan Agner
2018-04-16 18:02 ` Uwe Kleine-König
2018-04-16 18:02 ` Uwe Kleine-König
2018-04-16 9:54 ` Einar Vading
2018-04-16 9:54 ` Einar Vading
2018-04-16 9:57 ` Einar Vading
2018-04-16 9:57 ` Einar Vading
2018-04-16 10:35 ` Stefan Agner
2018-04-16 10:35 ` Stefan Agner
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