linux-kernel - [PATCH] USB: serial: pl2303: account for deficits of clones

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Message-ID: <a07922bd-4550-41d8-a7cd-8943baf6f8fb@siemens.com>
Date: Sun, 1 Sep 2024 23:11:29 +0200
From: Jan Kiszka <jan.kiszka@...mens.com>
To: Johan Hovold <johan@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: [PATCH] USB: serial: pl2303: account for deficits of clones

From: Jan Kiszka <jan.kiszka@...mens.com>

There are apparently incomplete clones of the HXD type chip in use.
Those return -EPIPE on GET_LINE_REQUEST and BREAK_REQUEST. Avoid
flooding the kernel log with those errors. Rather use the
line_settings cache for GET_LINE_REQUEST and signal missing support by
returning -ENOTTY from pl2303_set_break.

Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
---
 drivers/usb/serial/pl2303.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/usb/serial/pl2303.c b/drivers/usb/serial/pl2303.c
index d93f5d584557..04cafa819390 100644
--- a/drivers/usb/serial/pl2303.c
+++ b/drivers/usb/serial/pl2303.c
@@ -731,12 +731,13 @@ static int pl2303_get_line_request(struct usb_serial_port *port,
 				GET_LINE_REQUEST, GET_LINE_REQUEST_TYPE,
 				0, 0, buf, 7, 100);
 	if (ret != 7) {
-		dev_err(&port->dev, "%s - failed: %d\n", __func__, ret);
+		struct pl2303_private *priv = usb_get_serial_port_data(port);
 
-		if (ret >= 0)
-			ret = -EIO;
+		dev_dbg(&port->dev, "%s - failed, falling back on cache: %d\n",
+			__func__, ret);
+		memcpy(buf, priv->line_settings, 7);
 
-		return ret;
+		return 0;
 	}
 
 	dev_dbg(&port->dev, "%s - %7ph\n", __func__, buf);
@@ -1078,8 +1079,8 @@ static int pl2303_set_break(struct usb_serial_port *port, bool enable)
 				 BREAK_REQUEST, BREAK_REQUEST_TYPE, state,
 				 0, NULL, 0, 100);
 	if (result) {
-		dev_err(&port->dev, "error sending break = %d\n", result);
-		return result;
+		dev_dbg(&port->dev, "error sending break = %d\n", result);
+		return -ENOTTY;
 	}
 
 	return 0;
-- 
2.43.0