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From: Michael Hanselmann <public@hansmi.ch>
To: linux-usb@vger.kernel.org, Johan Hovold <johan@kernel.org>
Cc: Michael Hanselmann <public@hansmi.ch>,
	Michael Dreher <michael@5dot1.de>,
	Jonathan Olds <jontio@i4free.co.nz>
Subject: [PATCH v2 2/6] USB: serial: ch341: Add basis for quirk detection
Date: Tue, 31 Mar 2020 23:37:18 +0000	[thread overview]
Message-ID: <1e1ae0da6082bb528a44ef323d4e1d3733d38858.1585697281.git.public@hansmi.ch> (raw)
In-Reply-To: <cover.1585697281.git.public@hansmi.ch>

A subset of CH341 devices does not support all features, namely the
prescaler is limited to a reduced precision and there is no support for
sending a RS232 break condition. This patch adds a detection function
which will be extended to return quirk flags as they're implemented.

The author's affected device has an imprint of "340" on the
turquoise-colored plug, but not all such devices appear to be affected.

Signed-off-by: Michael Hanselmann <public@hansmi.ch>
---
 drivers/usb/serial/ch341.c | 49 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/usb/serial/ch341.c b/drivers/usb/serial/ch341.c
index 85e7125d0194..9c839f67c3d4 100644
--- a/drivers/usb/serial/ch341.c
+++ b/drivers/usb/serial/ch341.c
@@ -87,6 +87,7 @@ struct ch341_private {
 	u8 mcr;
 	u8 msr;
 	u8 lcr;
+	u8 quirks;
 };
 
 static void ch341_set_termios(struct tty_struct *tty,
@@ -330,6 +331,45 @@ out:	kfree(buffer);
 	return r;
 }
 
+static int ch341_detect_quirks(struct usb_device *dev)
+{
+	const unsigned int size = 2;
+	char *buffer;
+	int r;
+
+	buffer = kmalloc(size, GFP_KERNEL);
+	if (!buffer)
+		return -ENOMEM;
+
+	/*
+	 * A subset of CH34x devices does not support all features. The
+	 * prescaler is limited and there is no support for sending a RS232
+	 * break condition. A read failure when trying to set up the latter is
+	 * used to detect these devices.
+	 */
+	r = usb_control_msg(dev, usb_rcvctrlpipe(dev, 0), CH341_REQ_READ_REG,
+			    USB_TYPE_VENDOR | USB_RECIP_DEVICE | USB_DIR_IN,
+			    CH341_REG_BREAK, 0, buffer, size, DEFAULT_TIMEOUT);
+	if (r == -EPIPE) {
+		dev_dbg(&dev->dev, "%s - reading break condition register"
+			" failed (%d)\n", __func__, r);
+		r = 0;
+		goto out;
+	}
+
+	if (r < 0) {
+		dev_err(&dev->dev, "%s - USB control read error (%d)\n",
+			__func__, r);
+		goto out;
+	}
+
+	r = 0;
+
+out:
+	kfree(buffer);
+	return r;
+}
+
 static int ch341_port_probe(struct usb_serial_port *port)
 {
 	struct ch341_private *priv;
@@ -351,6 +391,15 @@ static int ch341_port_probe(struct usb_serial_port *port)
 	if (r < 0)
 		goto error;
 
+	r = ch341_detect_quirks(port->serial->dev);
+	if (r < 0)
+		goto error;
+	if (r != 0) {
+		dev_dbg(&port->serial->dev->dev,
+			"%s - enabling quirks flags %08x\n", __func__, r);
+		priv->quirks |= r;
+	}
+
 	usb_set_serial_port_data(port, priv);
 	return 0;
 
-- 
2.20.1


  parent reply	other threads:[~2020-03-31 23:37 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-31 23:37 [PATCH v2 0/6] USB: serial: ch341: Add support for limited chips (was: Add support for HL340 devices) Michael Hanselmann
2020-03-31 23:37 ` [PATCH v2 1/6] USB: serial: ch341: Reduce special cases in clock calculation Michael Hanselmann
2020-03-31 23:37 ` Michael Hanselmann [this message]
2020-05-14 14:09   ` [PATCH v2 2/6] USB: serial: ch341: Add basis for quirk detection Johan Hovold
2020-03-31 23:37 ` [PATCH v2 3/6] USB: serial: ch341: Limit prescaler on quirky chips Michael Hanselmann
2020-05-14 14:17   ` Johan Hovold
2020-05-27 13:16     ` Johan Hovold
2020-05-27 15:41       ` Michael Hanselmann
2020-05-29  7:15         ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 4/6] USB: serial: ch341: Name prescaler, divisor registers Michael Hanselmann
2020-05-14 14:24   ` Johan Hovold
2020-05-27 20:59     ` Michael Hanselmann
2020-06-29  9:51       ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 5/6] USB: serial: ch341: Compute minimum baud rate Michael Hanselmann
2020-05-27 22:19   ` Michael Hanselmann
2020-06-30  9:57     ` Johan Hovold
2020-03-31 23:37 ` [PATCH v2 6/6] USB: serial: ch341: Simulate break condition if not supported Michael Hanselmann
2020-05-14 14:47   ` Johan Hovold
2020-05-27 22:21     ` Michael Hanselmann
2020-06-30 11:39       ` Johan Hovold
2020-07-04 18:25         ` Michael Hanselmann
2020-07-06  9:31           ` Johan Hovold
2020-05-14 14:02 ` [PATCH v2 0/6] USB: serial: ch341: Add support for limited chips (was: Add support for HL340 devices) Johan Hovold

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