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Commit 7e1e6ced authored by Ian Abbott's avatar Ian Abbott Committed by Johan Hovold
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USB: serial: ftdi_sio: detect BM chip with iSerialNumber bug 



If a BM type chip has iSerialNumber set to 0 in its EEPROM, an incorrect
value is read from the bcdDevice field of the USB descriptor, making it
look like an AM type chip.  Attempt to correct this in
ftdi_determine_type() by attempting to read the latency timer for an AM
type chip if it has iSerialNumber set to 0.  If that succeeds, assume it
is a BM type chip.

Currently, read_latency_timer() bails out without reading the latency
timer for an AM type chip, so factor out the guts of
read_latency_timer() into a new function _read_latency_timer() that
attempts to read the latency timer regardless of chip type, and returns
either the latency timer value or a negative error number.

Signed-off-by: default avatarIan Abbott <abbotti@mev.co.uk>
Signed-off-by: default avatarJohan Hovold <johan@kernel.org>
parent 2dea7cd7

drivers/usb/serial/ftdi_sio.c

+33 −8
Original line number Diff line number Diff line
@@ -1425,16 +1425,13 @@ static int write_latency_timer(struct usb_serial_port *port) 
	return rv;

}



static int read_latency_timer(struct usb_serial_port *port)

static int _read_latency_timer(struct usb_serial_port *port)

{

	struct ftdi_private *priv = usb_get_serial_port_data(port);

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

	unsigned char *buf;

	int rv;



	if (priv->chip_type == SIO || priv->chip_type == FT8U232AM)

		return -EINVAL;



	buf = kmalloc(1, GFP_KERNEL);

	if (!buf)

		return -ENOMEM;
@@ -1446,11 +1443,10 @@ static int read_latency_timer(struct usb_serial_port *port) 
			     0, priv->interface,

			     buf, 1, WDR_TIMEOUT);

	if (rv < 1) {

		dev_err(&port->dev, "Unable to read latency timer: %i\n", rv);

		if (rv >= 0)

			rv = -EIO;

	} else {

		priv->latency = buf[0];

		rv = buf[0];

	}



	kfree(buf);
@@ -1458,6 +1454,25 @@ static int read_latency_timer(struct usb_serial_port *port) 
	return rv;

}



static int read_latency_timer(struct usb_serial_port *port)

{

	struct ftdi_private *priv = usb_get_serial_port_data(port);

	int rv;



	if (priv->chip_type == SIO || priv->chip_type == FT8U232AM)

		return -EINVAL;



	rv = _read_latency_timer(port);

	if (rv < 0) {

		dev_err(&port->dev, "Unable to read latency timer: %i\n", rv);

		return rv;

	}



	priv->latency = rv;



	return 0;

}



static int get_serial_info(struct usb_serial_port *port,

				struct serial_struct __user *retinfo)

{
@@ -1609,9 +1624,19 @@ static void ftdi_determine_type(struct usb_serial_port *port) 
		priv->baud_base = 12000000 / 16;

	} else if (version < 0x400) {

		/* Assume it's an FT8U232AM (or FT8U245AM) */

		/* (It might be a BM because of the iSerialNumber bug,

		 * but it will still work as an AM device.) */

		priv->chip_type = FT8U232AM;

		/*

		 * It might be a BM type because of the iSerialNumber bug.

		 * If iSerialNumber==0 and the latency timer is readable,

		 * assume it is BM type.

		 */

		if (udev->descriptor.iSerialNumber == 0 &&

				_read_latency_timer(port) >= 0) {

			dev_dbg(&port->dev,

				"%s: has latency timer so not an AM type\n",

				__func__);

			priv->chip_type = FT232BM;

		}

	} else if (version < 0x600) {

		/* Assume it's an FT232BM (or FT245BM) */

		priv->chip_type = FT232BM;