Commit c404bf4a authored by Michael Hanselmann's avatar Michael Hanselmann Committed by Johan Hovold
Browse files

USB: serial: ch341: add basis for quirk detection 



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 set 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: default avatarMichael Hanselmann <public@hansmi.ch>
Link: https://lore.kernel.org/r/1e1ae0da6082bb528a44ef323d4e1d3733d38858.1585697281.git.public@hansmi.ch


[ johan: use long type for quirks; rephrase and use port device for
	 messages; handle short reads; set quirk flags directly in
	 helper function ]
Cc: stable <stable@vger.kernel.org>	# 5.5
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
parent 986c1748

drivers/usb/serial/ch341.c

+53 −0
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ struct ch341_private { 
	u8 mcr;

	u8 msr;

	u8 lcr;

	unsigned long quirks;

};



static void ch341_set_termios(struct tty_struct *tty,
@@ -308,6 +309,53 @@ out: kfree(buffer); 
	return r;

}



static int ch341_detect_quirks(struct usb_serial_port *port)

{

	struct ch341_private *priv = usb_get_serial_port_data(port);

	struct usb_device *udev = port->serial->dev;

	const unsigned int size = 2;

	unsigned long quirks = 0;

	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(udev, usb_rcvctrlpipe(udev, 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(&port->dev, "break control not supported\n");

		r = 0;

		goto out;

	}



	if (r != size) {

		if (r >= 0)

			r = -EIO;

		dev_err(&port->dev, "failed to read break control: %d\n", r);

		goto out;

	}



	r = 0;

out:

	kfree(buffer);



	if (quirks) {

		dev_dbg(&port->dev, "enabling quirk flags: 0x%02lx\n", quirks);

		priv->quirks |= quirks;

	}



	return r;

}



static int ch341_port_probe(struct usb_serial_port *port)

{

	struct ch341_private *priv;
@@ -330,6 +378,11 @@ static int ch341_port_probe(struct usb_serial_port *port) 
		goto error;



	usb_set_serial_port_data(port, priv);



	r = ch341_detect_quirks(port);

	if (r < 0)

		goto error;



	return 0;



error:	kfree(priv);

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