V4L/DVB (11923): em28xx: Don't let device work unless connected to a high speed USB port

The em28xx basically just doesn't work at 12 Mbps.  The isoc pipe needs
nearly 200 Mbps for analog support, so users would see garbage video, and on
the DVB/ATSC side scanning is likely to work but if the user tried to tune it
would certainly appear to have failed.

It's better to fail explicity up front and tell the user to plug into a USB 2.0
port, than to let the driver load and the user have weird problems with tuning
and garbage video.
Signed-off-by: NDevin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/em28xx/em28xx-cards.c

@@ -2365,6 +2365,20 @@ static int em28xx_usb_probe(struct usb_interface *interface,
 		ifnum,
 		interface->altsetting->desc.bInterfaceNumber);
 
+	/*
+	 * Make sure we have 480 Mbps of bandwidth, otherwise things like
+	 * video stream wouldn't likely work, since 12 Mbps is generally
+	 * not enough even for most Digital TV streams.
+	 */
+	if (udev->speed != USB_SPEED_HIGH) {
+		printk(DRIVER_NAME ": Device initialization failed.\n");
+		printk(DRIVER_NAME ": Device must be connected to a high-speed"
+		       " USB 2.0 port.\n");
+		em28xx_devused &= ~(1<<nr);
+		retval = -ENODEV;
+		goto err;
+	}
+
 	if (nr >= EM28XX_MAXBOARDS) {
 		printk(DRIVER_NAME ": Supports only %i em28xx boards.\n",
 				EM28XX_MAXBOARDS);