linux-kernel - [PATCH 2 1/9] serial: core: move RS485 configuration tasks from drivers into core

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Date:   Wed, 16 Feb 2022 01:17:55 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     gregkh@...uxfoundation.org, jirislaby@...nel.org,
        u.kleine-koenig@...gutronix.de
Cc:     linux@...linux.org.uk, richard.genoud@...il.com,
        nicolas.ferre@...rochip.com, alexandre.belloni@...tlin.com,
        ludovic.desroches@...rochip.com, shawnguo@...nel.org,
        s.hauer@...gutronix.de, kernel@...gutronix.de, festevam@...il.com,
        linux-imx@....com, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-stm32@...md-mailman.stormreply.com, lukas@...ner.de,
        Lino Sanfilippo <LinoSanfilippo@....de>
Subject: [PATCH 2 1/9] serial: core: move RS485 configuration tasks from drivers into core

Several drivers that support setting the RS485 configuration via userspace
implement one or more of the following tasks:

- in case of an invalid RTS configuration (both RTS after send and RTS on
  send set or both unset) fall back to enable RTS on send and disable RTS
  after send

- nullify the padding field of the returned serial_rs485 struct

- copy the configuration into the uart port struct

- limit RTS delays to 100 ms

Move these tasks into the serial core to make them generic and to provide
a consistent behaviour among all drivers.

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
---
 drivers/tty/serial/serial_core.c | 18 ++++++++++++++++++
 include/uapi/linux/serial.h      |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 846192a7b4bf..a4f7e847d414 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1282,8 +1282,26 @@ static int uart_set_rs485_config(struct uart_port *port,
 	if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
 		return -EFAULT;
 
+	/* pick sane settings if the user hasn't */
+	if (!(rs485.flags & SER_RS485_RTS_ON_SEND) ==
+	    !(rs485.flags & SER_RS485_RTS_AFTER_SEND)) {
+		rs485.flags |= SER_RS485_RTS_ON_SEND;
+		rs485.flags &= ~SER_RS485_RTS_AFTER_SEND;
+	}
+
+	rs485.delay_rts_before_send = min_t(unsigned int,
+					    rs485.delay_rts_before_send,
+					    SER_RS485_MAX_RTS_DELAY);
+	rs485.delay_rts_after_send = min_t(unsigned int,
+					   rs485.delay_rts_after_send,
+					   SER_RS485_MAX_RTS_DELAY);
+	/* Return clean padding area to userspace */
+	memset(rs485.padding, 0, sizeof(rs485.padding));
+
 	spin_lock_irqsave(&port->lock, flags);
 	ret = port->rs485_config(port, &rs485);
+	if (!ret)
+		port->rs485 = rs485;
 	spin_unlock_irqrestore(&port->lock, flags);
 	if (ret)
 		return ret;
diff --git a/include/uapi/linux/serial.h b/include/uapi/linux/serial.h
index fa6b16e5fdd8..859045a53231 100644
--- a/include/uapi/linux/serial.h
+++ b/include/uapi/linux/serial.h
@@ -128,6 +128,9 @@ struct serial_rs485 {
 							   (if supported) */
 	__u32	delay_rts_before_send;	/* Delay before send (milliseconds) */
 	__u32	delay_rts_after_send;	/* Delay after send (milliseconds) */
+#define SER_RS485_MAX_RTS_DELAY		100		/* Max time with active
+							   RTS before/after
+							   data sent (msecs) */
 	__u32	padding[5];		/* Memory is cheap, new structs
 					   are a royal PITA .. */
 };

base-commit: 802d00bd774b77fe132e9e83462b96fb9919411c
-- 
2.34.1