[media] au0828: Only alt setting logic when needed

It seems that there's a bug at au0828 hardware/firmware
related to alternate setting: when the device is already at
alt 5, a further call causes the URBs to receive -ESHUTDOWN.

I found two different encarnations of this issue:

1) at qv4l2, it fails the second time we try to open the
video screen;
2) at xawtv, when audio underrun occurs, with is very
frequent, at least on my test machine.

The fix is simple: just check if alt=5 before calling
set_usb_interface().

Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/au0828/au0828-video.c

@@ -787,11 +787,27 @@ static int au0828_i2s_init(struct au0828_dev *dev)
 
 /*
  * Auvitek au0828 analog stream enable
- * Please set interface0 to AS5 before enable the stream
  */
 static int au0828_analog_stream_enable(struct au0828_dev *d)
 {
+	struct usb_interface *iface;
+	int ret;
+
 	dprintk(1, "au0828_analog_stream_enable called\n");
+
+	iface = usb_ifnum_to_if(d->usbdev, 0);
+	if (iface && iface->cur_altsetting->desc.bAlternateSetting != 5) {
+		dprintk(1, "Changing intf#0 to alt 5\n");
+		/* set au0828 interface0 to AS5 here again */
+		ret = usb_set_interface(d->usbdev, 0, 5);
+		if (ret < 0) {
+			printk(KERN_INFO "Au0828 can't set alt setting to 5!\n");
+			return -EBUSY;
+		}
+	}
+
+	/* FIXME: size should be calculated using d->width, d->height */
+
 	au0828_writereg(d, AU0828_SENSORCTRL_VBI_103, 0x00);
 	au0828_writereg(d, 0x106, 0x00);
 	/* set x position */
@@ -1002,15 +1018,6 @@ static int au0828_v4l2_open(struct file *filp)
 		return -ERESTARTSYS;
 	}
 	if (dev->users == 0) {
-		/* set au0828 interface0 to AS5 here again */
-		ret = usb_set_interface(dev->usbdev, 0, 5);
-		if (ret < 0) {
-			mutex_unlock(&dev->lock);
-			printk(KERN_INFO "Au0828 can't set alternate to 5!\n");
-			kfree(fh);
-			return -EBUSY;
-		}
-
 		au0828_analog_stream_enable(dev);
 		au0828_analog_stream_reset(dev);
 
@@ -1252,13 +1259,6 @@ static int au0828_set_format(struct au0828_dev *dev, unsigned int cmd,
 		}
 	}
 
-	/* set au0828 interface0 to AS5 here again */
-	ret = usb_set_interface(dev->usbdev, 0, 5);
-	if (ret < 0) {
-		printk(KERN_INFO "Au0828 can't set alt setting to 5!\n");
-		return -EBUSY;
-	}
-
 	au0828_analog_stream_enable(dev);
 
 	return 0;