[RS485 in UART2 with RTS Pin]

I suggest you check if UART2 RTS is working on this hardware/software first. You can connecting some state indicator (LED, voltmeter, ...) to its pin and manual change RTS state (eg. Ctrl-A Ctrl-G in picocom).

 

If RTS work OK you can try my patch. I'm not familiar with NanoPi Neo Core and I don't know how serial hardware is on its chip, so if it's not compatible with 8250_dw patch will not work. To use my patch you must build your own kernel image (https://docs.armbian.com/Developer-Guide_Build-Preparation/) with applying this patch (put it to "patch/kernel/sunxi-current" should do this).

[RTS signal and uart2 init]

On 11/1/2021 at 6:51 PM, martinayotte said:

 

I don't know ... I've worked on this since almost a year ...

So ... I was trying to look too.

 

Looks like this patch (series) make mess with your rs485-8250 patch, but don't enable software emulated rs485 for dw variant nor provide own workaround for chips without "end transmit" interrupt.

 

I created minimal patch for add this workaround (from your patch) to current kernel:

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index 9c00d7504..bc8cd87ee 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -469,6 +469,10 @@ static int dw8250_probe(struct platform_device *pdev)
 	p->set_ldisc	= dw8250_set_ldisc;
 	p->set_termios	= dw8250_set_termios;
 
+	p->rs485_config = serial8250_em485_config;
+	up->rs485_start_tx = serial8250_em485_start_tx;
+	up->rs485_stop_tx = serial8250_em485_stop_tx;
+
 	p->membase = devm_ioremap(dev, regs->start, resource_size(regs));
 	if (!p->membase)
 		return -ENOMEM;
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index be779eb9e..c9f5b626e 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1541,8 +1541,14 @@ static inline void __stop_tx(struct uart_8250_port *p)
 		 * shift register are empty. It is for device driver to enable
 		 * interrupt on TEMT.
 		 */
-		if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
-			return;
+		//if ((lsr & BOTH_EMPTY) != BOTH_EMPTY)
+		//	return;
+		// TODO: use if / while variant depending on the support / not support interrupt ...
+		// TODO: or provide different serial8250_stop_tx for chips without interrupt
+		while ((lsr & BOTH_EMPTY) != BOTH_EMPTY) {
+			lsr = serial_in(p, UART_LSR);
+			cpu_relax();
+		}
 
 		__stop_tx_rs485(p);
 	}

This is more "dirty hack" than "good patch" (always use "no interrupt" approach - see todo note in code), but it's work for me (at least for now, more tests shortly).

[RTS signal and uart2 init]

On 8/20/2020 at 12:26 PM, martinayotte said:

I'm still investigating how to make it work again and/or make the someone else patch working as my previous one ...

 

Hi,

 

do you update/fix rs485-8250 patch for current kernel (5.10)?