linux-kernel - [PATCH] serial: sc16is7xx: announce support for SER_RS485_RTS_ON

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Message-Id: <20241007162716.3122912-1-hugo@hugovil.com>
Date: Mon,  7 Oct 2024 12:27:15 -0400
From: Hugo Villeneuve <hugo@...ovil.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>
Cc: hugo@...ovil.com,
	andriy.shevchenko@...ux.intel.com,
	Hugo Villeneuve <hvilleneuve@...onoff.com>,
	Konstantin Pugin <ria.freelander@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: [PATCH] serial: sc16is7xx: announce support for SER_RS485_RTS_ON_SEND

From: Hugo Villeneuve <hvilleneuve@...onoff.com>

When specifying flag SER_RS485_RTS_ON_SEND in RS485 configuration,
we get the following warning after commit 4afeced55baa ("serial: core:
fix sanitizing check for RTS settings"):

    invalid RTS setting, using RTS_AFTER_SEND instead

This results in SER_RS485_RTS_AFTER_SEND being set and the
driver always write to the register field SC16IS7XX_EFCR_RTS_INVERT_BIT,
which breaks some hardware using these chips.

The hardware supports both RTS_ON_SEND and RTS_AFTER_SEND modes, so fix
this by announcing support for RTS_ON_SEND.

Signed-off-by: Hugo Villeneuve <hvilleneuve@...onoff.com>
Suggested-by: Konstantin Pugin <ria.freelander@...il.com>
Link: https://lore.kernel.org/lkml/20240422133219.2710061-2-ria.freelander@gmail.com
---

This patch was part of a series to add support for a new EXAR variant by
Konstantin, but the final version was never submitted. I need this patch
for a new revision of our board which has reverse RTS signal compared to the
old revision.
---
 drivers/tty/serial/sc16is7xx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index ad88a33a504f..9d0c971e49f5 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1473,7 +1473,7 @@ static int sc16is7xx_setup_mctrl_ports(struct sc16is7xx_port *s,
 }
 
 static const struct serial_rs485 sc16is7xx_rs485_supported = {
-	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND,
+	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
 	.delay_rts_before_send = 1,
 	.delay_rts_after_send = 1,	/* Not supported but keep returning -EINVAL */
 };

base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
-- 
2.39.5