When using half-duplex mode (which disables receiver during txing)
the RTS signal cannot be driven low during transmission. This seems
to be a limitation of the i.MX UART IP: The RTS (CTS_B) signal is
controlled by the receiver. When the receiver is disabled, the
signal stays in UART logic idle state which is high...
If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during
transmission. Since this is the default state of the RTS (CTS_B)
signal when the receiver is off, half-duplex mode in this
configuration works fine.
However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set)
cannot be generated when the receiver is turned off.
Print an error if the user selects this unsupported configuration
(both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and
configure the closest working configuration (set the
SER_RS485_RX_DURING_TX flag).
Signed-off-by: Stefan Agner <[email protected]>
---
Changes since v1:
- Consistently check for sport->have_rtscts && !(rs485conf->flags &
SER_RS485_RTS_ON_SEND)
- Don't break printed message
drivers/tty/serial/imx.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 91f3a1a5cb7f..1c1080fc8084 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -1833,6 +1833,11 @@ static int imx_uart_rs485_config(struct uart_port *port,
rs485conf->flags &= ~SER_RS485_ENABLED;
if (rs485conf->flags & SER_RS485_ENABLED) {
+ /* Enable receiver if low-active RTS signal is requested */
+ if (sport->have_rtscts &&
+ !(rs485conf->flags & SER_RS485_RTS_ON_SEND))
+ rs485conf->flags |= SER_RS485_RX_DURING_TX;
+
/* disable transmitter */
ucr2 = imx_uart_readl(sport, UCR2);
if (rs485conf->flags & SER_RS485_RTS_AFTER_SEND)
@@ -2265,6 +2270,16 @@ static int imx_uart_probe(struct platform_device *pdev)
(!sport->have_rtscts && !sport->have_rtsgpio))
dev_err(&pdev->dev, "no RTS control, disabling rs485\n");
+ /*
+ * The RTS (CTS_B) signal cannot be set low during transmission
+ * in case the receiver is off (limitation of the i.MX UART IP).
+ */
+ if (sport->port.rs485.flags & SER_RS485_ENABLED && sport->have_rtscts &&
+ (!(sport->port.rs485.flags & SER_RS485_RTS_ON_SEND) &&
+ !(sport->port.rs485.flags & SER_RS485_RX_DURING_TX)))
+ dev_err(&pdev->dev,
+ "low-active RTS not possible when receiver is off, enabling receiver\n");
+
imx_uart_rs485_config(&sport->port, &sport->port.rs485);
/* Disable interrupts before requesting them */
--
2.17.0
On Wed, Apr 18, 2018 at 04:06:38PM +0200, Stefan Agner wrote:
> When using half-duplex mode (which disables receiver during txing)
> the RTS signal cannot be driven low during transmission. This seems
> to be a limitation of the i.MX UART IP: The RTS (CTS_B) signal is
> controlled by the receiver. When the receiver is disabled, the
> signal stays in UART logic idle state which is high...
>
> If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during
> transmission. Since this is the default state of the RTS (CTS_B)
> signal when the receiver is off, half-duplex mode in this
> configuration works fine.
>
> However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set)
> cannot be generated when the receiver is turned off.
>
> Print an error if the user selects this unsupported configuration
> (both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and
> configure the closest working configuration (set the
> SER_RS485_RX_DURING_TX flag).
>
> Signed-off-by: Stefan Agner <[email protected]>
> ---
> Changes since v1:
> - Consistently check for sport->have_rtscts && !(rs485conf->flags &
> SER_RS485_RTS_ON_SEND)
> - Don't break printed message
>
> drivers/tty/serial/imx.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 91f3a1a5cb7f..1c1080fc8084 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -1833,6 +1833,11 @@ static int imx_uart_rs485_config(struct uart_port *port,
> rs485conf->flags &= ~SER_RS485_ENABLED;
>
> if (rs485conf->flags & SER_RS485_ENABLED) {
> + /* Enable receiver if low-active RTS signal is requested */
> + if (sport->have_rtscts &&
> + !(rs485conf->flags & SER_RS485_RTS_ON_SEND))
> + rs485conf->flags |= SER_RS485_RX_DURING_TX;
> +
I wonder what should happen, if the device tree has both
uart-has-rtscts;
rts-gpios = <...>;
. I think the right thing would be to check for
sport->have_rtscts && !sport->have_rtsgpio
.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-K?nig |
Industrial Linux Solutions | http://www.pengutronix.de/ |
On 18.04.2018 16:53, Uwe Kleine-König wrote:
> On Wed, Apr 18, 2018 at 04:06:38PM +0200, Stefan Agner wrote:
>> When using half-duplex mode (which disables receiver during txing)
>> the RTS signal cannot be driven low during transmission. This seems
>> to be a limitation of the i.MX UART IP: The RTS (CTS_B) signal is
>> controlled by the receiver. When the receiver is disabled, the
>> signal stays in UART logic idle state which is high...
>>
>> If SER_RS485_RTS_ON_SEND is used, RTS needs to be high active during
>> transmission. Since this is the default state of the RTS (CTS_B)
>> signal when the receiver is off, half-duplex mode in this
>> configuration works fine.
>>
>> However, a low-active RTS signal (flag SER_RS485_RTS_ON_SEND not set)
>> cannot be generated when the receiver is turned off.
>>
>> Print an error if the user selects this unsupported configuration
>> (both SER_RS485_RTS_ON_SEND and SER_RS485_RX_DURING_TX unset) and
>> configure the closest working configuration (set the
>> SER_RS485_RX_DURING_TX flag).
>>
>> Signed-off-by: Stefan Agner <[email protected]>
>> ---
>> Changes since v1:
>> - Consistently check for sport->have_rtscts && !(rs485conf->flags &
>> SER_RS485_RTS_ON_SEND)
>> - Don't break printed message
>>
>> drivers/tty/serial/imx.c | 15 +++++++++++++++
>> 1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
>> index 91f3a1a5cb7f..1c1080fc8084 100644
>> --- a/drivers/tty/serial/imx.c
>> +++ b/drivers/tty/serial/imx.c
>> @@ -1833,6 +1833,11 @@ static int imx_uart_rs485_config(struct uart_port *port,
>> rs485conf->flags &= ~SER_RS485_ENABLED;
>>
>> if (rs485conf->flags & SER_RS485_ENABLED) {
>> + /* Enable receiver if low-active RTS signal is requested */
>> + if (sport->have_rtscts &&
>> + !(rs485conf->flags & SER_RS485_RTS_ON_SEND))
>> + rs485conf->flags |= SER_RS485_RX_DURING_TX;
>> +
>
> I wonder what should happen, if the device tree has both
>
> uart-has-rtscts;
> rts-gpios = <...>;
Hm, it seems that the code controls both in that case.
>
> . I think the right thing would be to check for
>
> sport->have_rtscts && !sport->have_rtsgpio
I agree, since it controls both one can use the GPIO to have a working
half duplex with low-active RTS configuration.
Will send v3.
--
Stefan