linux-kernel - [PATCH 2/6] USB: serial: cp210x: fix flow-control error handling

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Message-Id: <20210702134227.24621-3-johan@kernel.org>
Date:   Fri,  2 Jul 2021 15:42:23 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Johan Hovold <johan@...nel.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH 2/6] USB: serial: cp210x: fix flow-control error handling

Make sure that the driver crtscts state is not updated in the unlikely
event that the flow-control request fails. Not doing so could break RTS
control.

Fixes: 5951b8508855 ("USB: serial: cp210x: suppress modem-control errors")
Cc: stable@...r.kernel.org	# 5.11
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/serial/cp210x.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index b41e2c7649fb..eb3be4f65603 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -1191,6 +1191,7 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
 	struct cp210x_flow_ctl flow_ctl;
 	u32 flow_repl;
 	u32 ctl_hs;
+	bool crtscts;
 	int ret;
 
 	/*
@@ -1246,14 +1247,14 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
 			flow_repl |= CP210X_SERIAL_RTS_FLOW_CTL;
 		else
 			flow_repl |= CP210X_SERIAL_RTS_INACTIVE;
-		port_priv->crtscts = true;
+		crtscts = true;
 	} else {
 		ctl_hs &= ~CP210X_SERIAL_CTS_HANDSHAKE;
 		if (port_priv->rts)
 			flow_repl |= CP210X_SERIAL_RTS_ACTIVE;
 		else
 			flow_repl |= CP210X_SERIAL_RTS_INACTIVE;
-		port_priv->crtscts = false;
+		crtscts = false;
 	}
 
 	if (I_IXOFF(tty)) {
@@ -1276,8 +1277,12 @@ static void cp210x_set_flow_control(struct tty_struct *tty,
 	flow_ctl.ulControlHandshake = cpu_to_le32(ctl_hs);
 	flow_ctl.ulFlowReplace = cpu_to_le32(flow_repl);
 
-	cp210x_write_reg_block(port, CP210X_SET_FLOW, &flow_ctl,
+	ret = cp210x_write_reg_block(port, CP210X_SET_FLOW, &flow_ctl,
 			sizeof(flow_ctl));
+	if (ret)
+		goto out_unlock;
+
+	port_priv->crtscts = crtscts;
 out_unlock:
 	mutex_unlock(&port_priv->mutex);
 }
-- 
2.31.1