linux-kernel - [PATCH stable-5.15 1/2] USB: serial: ch341: fix lost character on LCR updates

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Message-Id: <20220906122127.31321-2-johan@kernel.org>
Date:   Tue,  6 Sep 2022 14:21:26 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        Johan Hovold <johan@...nel.org>,
        Jonathan Woithe <jwoithe@...t42.net>
Subject: [PATCH stable-5.15 1/2] USB: serial: ch341: fix lost character on LCR updates

commit 8e83622ae7ca481c76c8fd9579877f6abae64ca2 upstream.

Disable LCR updates for pre-0x30 devices which use a different (unknown)
protocol for line control and where the current register write causes
the next received character to be lost.

Note that updating LCR using the INIT command has no effect on these
devices either.

Reported-by: Jonathan Woithe <jwoithe@...t42.net>
Tested-by: Jonathan Woithe <jwoithe@...t42.net>
Link: https://lore.kernel.org/r/Ys1iPTfiZRWj2gXs@marvin.atrad.com.au
Fixes: 4e46c410e050 ("USB: serial: ch341: reinitialize chip on reconfiguration")
Fixes: 55fa15b5987d ("USB: serial: ch341: fix baud rate and line-control handling")
Cc: stable@...r.kernel.org      # 4.10
Signed-off-by: Johan Hovold <johan@...nel.org>
[ johan: adjust context to 5.15 ]
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/serial/ch341.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index b5a1864e9cfd..b787533aec64 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -97,7 +97,10 @@ struct ch341_private {
 	u8 mcr;
 	u8 msr;
 	u8 lcr;
+
 	unsigned long quirks;
+	u8 version;
+
 	unsigned long break_end;
 };
 
@@ -271,6 +274,9 @@ static int ch341_set_baudrate_lcr(struct usb_device *dev,
 	 * (stop bits, parity and word length). Version 0x30 and above use
 	 * CH341_REG_LCR only and CH341_REG_LCR2 is always set to zero.
 	 */
+	if (priv->version < 0x30)
+		return 0;
+
 	r = ch341_control_out(dev, CH341_REQ_WRITE_REG,
 			      CH341_REG_LCR2 << 8 | CH341_REG_LCR, lcr);
 	if (r)
@@ -323,7 +329,9 @@ static int ch341_configure(struct usb_device *dev, struct ch341_private *priv)
 	r = ch341_control_in(dev, CH341_REQ_READ_VERSION, 0, 0, buffer, size);
 	if (r < 0)
 		goto out;
-	dev_dbg(&dev->dev, "Chip version: 0x%02x\n", buffer[0]);
+
+	priv->version = buffer[0];
+	dev_dbg(&dev->dev, "Chip version: 0x%02x\n", priv->version);
 
 	r = ch341_control_out(dev, CH341_REQ_SERIAL_INIT, 0, 0);
 	if (r < 0)
-- 
2.35.1