[PATCH] USB: usblp printer GET_DEVICE_ID fix

There is a problem in the usblp GET_DEVICE_ID ioctl() implementation. The patch
below (against 2.6 current) fixes the code to be according to the official usb
printer spec.

Most printers are not affected by this fix, as they use interface 0 and
alternate 0. For those, nothing changes. But my printer/scanner uses interface
1 for the printer.

drivers/usb/class/usblp.c

@@ -226,11 +226,21 @@ extern struct usb_driver usblp_driver;
 
 static int usblp_ctrl_msg(struct usblp *usblp, int request, int type, int dir, int recip, int value, void *buf, int len)
 {
-	int retval = usb_control_msg(usblp->dev,
+	int retval;
+	int index = usblp->ifnum;
+
+	/* High byte has the interface index.
+	   Low byte has the alternate setting.
+	 */
+	if ((request == USBLP_REQ_GET_ID) && (type == USB_TYPE_CLASS)) {
+	  index = (usblp->ifnum<<8)|usblp->protocol[usblp->current_protocol].alt_setting;
+	}
+
+	retval = usb_control_msg(usblp->dev,
 		dir ? usb_rcvctrlpipe(usblp->dev, 0) : usb_sndctrlpipe(usblp->dev, 0),
-		request, type | dir | recip, value, usblp->ifnum, buf, len, USBLP_WRITE_TIMEOUT);
-	dbg("usblp_control_msg: rq: 0x%02x dir: %d recip: %d value: %d len: %#x result: %d",
-		request, !!dir, recip, value, len, retval);
+		request, type | dir | recip, value, index, buf, len, USBLP_WRITE_TIMEOUT);
+	dbg("usblp_control_msg: rq: 0x%02x dir: %d recip: %d value: %d idx: %d len: %#x result: %d",
+		request, !!dir, recip, value, index, len, retval);
 	return retval < 0 ? retval : 0;
 }
 
@@ -440,6 +450,9 @@ static int usblp_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
 		goto done;
 	}
 
+	dbg("usblp_ioctl: cmd=0x%x (%c nr=%d len=%d dir=%d)", cmd, _IOC_TYPE(cmd),
+		_IOC_NR(cmd), _IOC_SIZE(cmd), _IOC_DIR(cmd) );
+
 	if (_IOC_TYPE(cmd) == 'P')	/* new-style ioctl number */
 
 		switch (_IOC_NR(cmd)) {