Linux Serial subsystem development

* [PATCH v3 6/7] serial: imx: set_mctrl(): correctly restore autoRTS state
From: Sergey Organov @ 2019-07-04 13:00 UTC (permalink / raw)
  To: linux-serial
  Cc: Greg Kroah-Hartman, Sascha Hauer, Sergey Organov, NXP Linux Team,
	Pengutronix Kernel Team, Uwe Kleine-König, linux-arm-kernel
In-Reply-To: <1562245229-709-1-git-send-email-sorganov@gmail.com>

imx_uart_set_mctrl() happened to set UCR2_CTSC bit whenever TIOCM_RTS
was set, no matter if RTS/CTS handshake is enabled or not. Now fixed by
turning handshake on only when CRTSCTS bit for the port is set.

Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Sergey Organov <sorganov@gmail.com>
---
 drivers/tty/serial/imx.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 5532887..582a3fd 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -970,10 +970,22 @@ static void imx_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	if (!(port->rs485.flags & SER_RS485_ENABLED)) {
 		u32 ucr2;
 
+		/*
+		 * Turn off autoRTS if RTS is lowered and restore autoRTS
+		 * setting if RTS is raised.
+		 */
 		ucr2 = imx_uart_readl(sport, UCR2);
 		ucr2 &= ~(UCR2_CTS | UCR2_CTSC);
-		if (mctrl & TIOCM_RTS)
-			ucr2 |= UCR2_CTS | UCR2_CTSC;
+		if (mctrl & TIOCM_RTS) {
+			ucr2 |= UCR2_CTS;
+			/*
+			 * UCR2_IRTS is unset if and only if the port is
+			 * configured for CRTSCTS, so we use inverted UCR2_IRTS
+			 * to get the state to restore to.
+			 */
+			if (!(ucr2 & UCR2_IRTS))
+				ucr2 |= UCR2_CTSC;
+		}
 		imx_uart_writel(sport, ucr2, UCR2);
 	}
 
-- 
2.10.0.1.g57b01a3

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