[PATCH] tty: serial: imx: Fix broken RS485

[PATCH] tty: serial: imx: Fix broken RS485

[Rickard Andersson]

From: Rickard x Andersson <rickaran@axis.com>

When about to transmit the function imx_uart_start_tx is called and in
some RS485 configurations this function will call imx_uart_stop_rx. The
problem is that imx_uart_stop_rx will enable loopback and when loopback
is enabled transmitted data will just be looped to RX.

This patch fixes the above problem by explicitly disabling loopback in
the case described above.

Signed-off-by: Rickard x Andersson <rickaran@axis.com>
---
 drivers/tty/serial/imx.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 4aa72d5aeafb..899e331bdfc8 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
 			imx_uart_writel(sport, ucr2, UCR2);
 
 			if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
-			    !port->rs485_rx_during_tx_gpio)
+			    !port->rs485_rx_during_tx_gpio) {
 				imx_uart_stop_rx(port);
+				/*
+				 * The function imx_uart_stop_rx right above
+				 * will enable loopback, but since we are just
+				 * about to transmit then disable loopback.
+				 */
+				imx_uart_disable_loopback_rs485(sport);
+			}
 
 			sport->tx_state = WAIT_AFTER_RTS;
 
-- 
2.30.2

Re: [PATCH] tty: serial: imx: Fix broken RS485

[Marek Vasut]

On 2/16/24 13:46, Rickard Andersson wrote:
> From: Rickard x Andersson <rickaran@axis.com>
> 
> When about to transmit the function imx_uart_start_tx is called and in
> some RS485 configurations this function will call imx_uart_stop_rx. The
> problem is that imx_uart_stop_rx will enable loopback and when loopback
> is enabled transmitted data will just be looped to RX.
> 
> This patch fixes the above problem by explicitly disabling loopback in
> the case described above.
> 
> Signed-off-by: Rickard x Andersson <rickaran@axis.com>

Fixes: tag is missing.

> ---
>   drivers/tty/serial/imx.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 4aa72d5aeafb..899e331bdfc8 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
>   			imx_uart_writel(sport, ucr2, UCR2);
>   
>   			if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
> -			    !port->rs485_rx_during_tx_gpio)
> +			    !port->rs485_rx_during_tx_gpio) {
>   				imx_uart_stop_rx(port);
> +				/*
> +				 * The function imx_uart_stop_rx right above
> +				 * will enable loopback, but since we are just
> +				 * about to transmit then disable loopback.
> +				 */
> +				imx_uart_disable_loopback_rs485(sport);
> +			}

Maybe it would be better to update the stop_rx and add parameter, 
whether it should/shouldn't enable the loopback ?

Re: [PATCH] tty: serial: imx: Fix broken RS485

[Rickard X Andersson]

On Fri, Feb 16, 2024 at 4:17 PM Marek Vasut <marex@denx.de> wrote:
>
> On 2/16/24 13:46, Rickard Andersson wrote:
> > From: Rickard x Andersson <rickaran@axis.com>
> >
> > When about to transmit the function imx_uart_start_tx is called and in
> > some RS485 configurations this function will call imx_uart_stop_rx. The
> > problem is that imx_uart_stop_rx will enable loopback and when loopback
> > is enabled transmitted data will just be looped to RX.
> >
> > This patch fixes the above problem by explicitly disabling loopback in
> > the case described above.
> >
> > Signed-off-by: Rickard x Andersson <rickaran@axis.com>
>
> Fixes: tag is missing.

Ok, I will add.
>
> > ---
> >   drivers/tty/serial/imx.c | 9 ++++++++-
> >   1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> > index 4aa72d5aeafb..899e331bdfc8 100644
> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
> >                       imx_uart_writel(sport, ucr2, UCR2);
> >
> >                       if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
> > -                         !port->rs485_rx_during_tx_gpio)
> > +                         !port->rs485_rx_during_tx_gpio) {
> >                               imx_uart_stop_rx(port);
> > +                             /*
> > +                              * The function imx_uart_stop_rx right above
> > +                              * will enable loopback, but since we are just
> > +                              * about to transmit then disable loopback.
> > +                              */
> > +                             imx_uart_disable_loopback_rs485(sport);
> > +                     }
>
> Maybe it would be better to update the stop_rx and add parameter,
> whether it should/shouldn't enable the loopback ?

Since *stop_rx is part of struct uart_ops I can not add an input argument to the function.

Best regards,
Rickard


________________________________________
From: Marek Vasut <marex@denx.de>
Sent: Friday, February 16, 2024 4:17 PM
To: Rickard X Andersson; linux-serial@vger.kernel.org; rickard314.andersson@gmail.com; gregkh@linuxfoundation.org; shawnguo@kernel.org; s.hauer@pengutronix.de; kernel@pengutronix.de; festevam@gmail.com; linux-imx@nxp.com; martin.fuzzey@flowbird.group; Christoph Niedermaier
Cc: kernel
Subject: Re: [PATCH] tty: serial: imx: Fix broken RS485

On 2/16/24 13:46, Rickard Andersson wrote:
> From: Rickard x Andersson <rickaran@axis.com>
>
> When about to transmit the function imx_uart_start_tx is called and in
> some RS485 configurations this function will call imx_uart_stop_rx. The
> problem is that imx_uart_stop_rx will enable loopback and when loopback
> is enabled transmitted data will just be looped to RX.
>
> This patch fixes the above problem by explicitly disabling loopback in
> the case described above.
>
> Signed-off-by: Rickard x Andersson <rickaran@axis.com>

Fixes: tag is missing.

> ---
>   drivers/tty/serial/imx.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 4aa72d5aeafb..899e331bdfc8 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
>                       imx_uart_writel(sport, ucr2, UCR2);
>
>                       if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
> -                         !port->rs485_rx_during_tx_gpio)
> +                         !port->rs485_rx_during_tx_gpio) {
>                               imx_uart_stop_rx(port);
> +                             /*
> +                              * The function imx_uart_stop_rx right above
> +                              * will enable loopback, but since we are just
> +                              * about to transmit then disable loopback.
> +                              */
> +                             imx_uart_disable_loopback_rs485(sport);
> +                     }

Maybe it would be better to update the stop_rx and add parameter,
whether it should/shouldn't enable the loopback ?

Re: [PATCH] tty: serial: imx: Fix broken RS485

[Marek Vasut]

On 2/20/24 07:07, Rickard X Andersson wrote:
> On Fri, Feb 16, 2024 at 4:17 PM Marek Vasut <marex@denx.de> wrote:
>>
>> On 2/16/24 13:46, Rickard Andersson wrote:
>>> From: Rickard x Andersson <rickaran@axis.com>
>>>
>>> When about to transmit the function imx_uart_start_tx is called and in
>>> some RS485 configurations this function will call imx_uart_stop_rx. The
>>> problem is that imx_uart_stop_rx will enable loopback and when loopback
>>> is enabled transmitted data will just be looped to RX.
>>>
>>> This patch fixes the above problem by explicitly disabling loopback in
>>> the case described above.
>>>
>>> Signed-off-by: Rickard x Andersson <rickaran@axis.com>
>>
>> Fixes: tag is missing.
> 
> Ok, I will add.
>>
>>> ---
>>>    drivers/tty/serial/imx.c | 9 ++++++++-
>>>    1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>>> index 4aa72d5aeafb..899e331bdfc8 100644
>>> --- a/drivers/tty/serial/imx.c
>>> +++ b/drivers/tty/serial/imx.c
>>> @@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
>>>                        imx_uart_writel(sport, ucr2, UCR2);
>>>
>>>                        if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
>>> -                         !port->rs485_rx_during_tx_gpio)
>>> +                         !port->rs485_rx_during_tx_gpio) {
>>>                                imx_uart_stop_rx(port);
>>> +                             /*
>>> +                              * The function imx_uart_stop_rx right above
>>> +                              * will enable loopback, but since we are just
>>> +                              * about to transmit then disable loopback.
>>> +                              */
>>> +                             imx_uart_disable_loopback_rs485(sport);
>>> +                     }
>>
>> Maybe it would be better to update the stop_rx and add parameter,
>> whether it should/shouldn't enable the loopback ?
> 
> Since *stop_rx is part of struct uart_ops I can not add an input argument to the function.

You could add a wrapper function and make stop_tx call that one.

Re: [PATCH] tty: serial: imx: Fix broken RS485

[Rickard X Andersson]

> >> Maybe it would be better to update the stop_rx and add parameter,
> >> whether it should/shouldn't enable the loopback ?
> >
> > Since *stop_rx is part of struct uart_ops I can not add an input argument to the function.
>
> You could add a wrapper function and make stop_tx call that one.

Ok, yes that is possible. Do you want me to do that change?

Best regards,
Rickard

________________________________________
From: Marek Vasut <marex@denx.de>
Sent: Tuesday, February 20, 2024 7:52 AM
To: Rickard X Andersson; linux-serial@vger.kernel.org; rickard314.andersson@gmail.com; gregkh@linuxfoundation.org; shawnguo@kernel.org; s.hauer@pengutronix.de; kernel@pengutronix.de; festevam@gmail.com; linux-imx@nxp.com; martin.fuzzey@flowbird.group; Christoph Niedermaier
Cc: kernel
Subject: Re: [PATCH] tty: serial: imx: Fix broken RS485

On 2/20/24 07:07, Rickard X Andersson wrote:
> On Fri, Feb 16, 2024 at 4:17 PM Marek Vasut <marex@denx.de> wrote:
>>
>> On 2/16/24 13:46, Rickard Andersson wrote:
>>> From: Rickard x Andersson <rickaran@axis.com>
>>>
>>> When about to transmit the function imx_uart_start_tx is called and in
>>> some RS485 configurations this function will call imx_uart_stop_rx. The
>>> problem is that imx_uart_stop_rx will enable loopback and when loopback
>>> is enabled transmitted data will just be looped to RX.
>>>
>>> This patch fixes the above problem by explicitly disabling loopback in
>>> the case described above.
>>>
>>> Signed-off-by: Rickard x Andersson <rickaran@axis.com>
>>
>> Fixes: tag is missing.
>
> Ok, I will add.
>>
>>> ---
>>>    drivers/tty/serial/imx.c | 9 ++++++++-
>>>    1 file changed, 8 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>>> index 4aa72d5aeafb..899e331bdfc8 100644
>>> --- a/drivers/tty/serial/imx.c
>>> +++ b/drivers/tty/serial/imx.c
>>> @@ -683,8 +683,15 @@ static void imx_uart_start_tx(struct uart_port *port)
>>>                        imx_uart_writel(sport, ucr2, UCR2);
>>>
>>>                        if (!(port->rs485.flags & SER_RS485_RX_DURING_TX) &&
>>> -                         !port->rs485_rx_during_tx_gpio)
>>> +                         !port->rs485_rx_during_tx_gpio) {
>>>                                imx_uart_stop_rx(port);
>>> +                             /*
>>> +                              * The function imx_uart_stop_rx right above
>>> +                              * will enable loopback, but since we are just
>>> +                              * about to transmit then disable loopback.
>>> +                              */
>>> +                             imx_uart_disable_loopback_rs485(sport);
>>> +                     }
>>
>> Maybe it would be better to update the stop_rx and add parameter,
>> whether it should/shouldn't enable the loopback ?
>
> Since *stop_rx is part of struct uart_ops I can not add an input argument to the function.

You could add a wrapper function and make stop_tx call that one.

Re: [PATCH] tty: serial: imx: Fix broken RS485

[Marek Vasut]

On 2/20/24 09:39, Rickard X Andersson wrote:
> 
>>>> Maybe it would be better to update the stop_rx and add parameter,
>>>> whether it should/shouldn't enable the loopback ?
>>>
>>> Since *stop_rx is part of struct uart_ops I can not add an input argument to the function.
>>
>> You could add a wrapper function and make stop_tx call that one.
> 
> Ok, yes that is possible. Do you want me to do that change?

Better wait a few days before sending V3, so that others can chime in. 
And yes, I think it would be better.