diff mbox series

[1/8] serial: core: only get RS485 termination gpio if supported

Message ID 20220622154659.8710-2-LinoSanfilippo@gmx.de
State New
Headers show
Series Fixes and cleanup for RS485 | expand

Commit Message

Lino Sanfilippo June 22, 2022, 3:46 p.m. UTC 
From: Lino Sanfilippo <l.sanfilippo@kunbus.com>

In uart_get_rs485_mode() only try to get a termination GPIO if RS485 bus
termination is supported by the driver.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@kunbus.com>
---
 drivers/tty/serial/serial_core.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

Comments

Lino Sanfilippo July 2, 2022, 4:50 p.m. UTC | #1 
Hi,

On 27.06.22 11:05, Ilpo Järvinen wrote:
> On Sat, 25 Jun 2022, Lukas Wunner wrote:

>>
>> I think what you want to do is amend uart_get_rs485_mode() to set
>> SER_RS485_TERMINATE_BUS in port->rs485_supported_flags if a GPIO
>> was found in the DT.  Instead of the change proposed above.

Agreed.

>
> That seems appropriate (and is a fix).
>
> What makes it a bit complicated though is that it's a pointer currently
> and what it points to is shared per driver (besides being const):
> 	const struct serial_rs485       *rs485_supported;
> While it could be embedded into uart_port, there's the .padding which we
> might not want to bloat uart_port with. Perhaps create non-uapi struct
> kserial_rs485 w/o .padding and add static_assert()s to ensure the
> layout is identical to serial_rs485?
>
>

This seems to be indeed the cleanest solution.

Regards,
Lino
diff mbox series

Patch

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 1368b0ef7d7f..015f4e1da647 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3384,17 +3384,20 @@  int uart_get_rs485_mode(struct uart_port *port)
 		rs485conf->flags |= SER_RS485_RTS_AFTER_SEND;
 	}
 
-	/*
-	 * Disabling termination by default is the safe choice:  Else if many
-	 * bus participants enable it, no communication is possible at all.
-	 * Works fine for short cables and users may enable for longer cables.
-	 */
-	port->rs485_term_gpio = devm_gpiod_get_optional(dev, "rs485-term",
-							GPIOD_OUT_LOW);
-	if (IS_ERR(port->rs485_term_gpio)) {
-		ret = PTR_ERR(port->rs485_term_gpio);
-		port->rs485_term_gpio = NULL;
-		return dev_err_probe(dev, ret, "Cannot get rs485-term-gpios\n");
+	if (port->rs485_supported->flags & SER_RS485_TERMINATE_BUS) {
+		/*
+		 * Disabling termination by default is the safe choice:  Else if
+		 * many bus participants enable it, no communication is possible
+		 * at all. Works fine for short cables and users may enable for
+		 * longer cables.
+		 */
+		port->rs485_term_gpio = devm_gpiod_get_optional(dev, "rs485-term",
+								GPIOD_OUT_LOW);
+		if (IS_ERR(port->rs485_term_gpio)) {
+			ret = PTR_ERR(port->rs485_term_gpio);
+			port->rs485_term_gpio = NULL;
+			return dev_err_probe(dev, ret, "Cannot get rs485-term-gpios\n");
+		}
 	}
 
 	return 0;