uvcvideo: uvc_scan_fallback() for webcams with broken chain

	return buffer;

}

static struct uvc_video_chain *uvc_alloc_chain(struct uvc_device *dev)

{

	struct uvc_video_chain *chain;

	chain = kzalloc(sizeof(*chain), GFP_KERNEL);

	if (chain == NULL)

		return NULL;

	INIT_LIST_HEAD(&chain->entities);

	mutex_init(&chain->ctrl_mutex);

	chain->dev = dev;

	v4l2_prio_init(&chain->prio);

	return chain;

}

/*

 * Fallback heuristic for devices that don't connect units and terminals in a

 * valid chain.

 *

 * Some devices have invalid baSourceID references, causing uvc_scan_chain()

 * to fail, but if we just take the entities we can find and put them together

 * in the most sensible chain we can think of, turns out they do work anyway.

 * Note: This heuristic assumes there is a single chain.

 *

 * At the time of writing, devices known to have such a broken chain are

 *  - Acer Integrated Camera (5986:055a)

 *  - Realtek rtl157a7 (0bda:57a7)

 */

static int uvc_scan_fallback(struct uvc_device *dev)

{

	struct uvc_video_chain *chain;

	struct uvc_entity *iterm = NULL;

	struct uvc_entity *oterm = NULL;

	struct uvc_entity *entity;

	struct uvc_entity *prev;

	/*

	 * Start by locating the input and output terminals. We only support

	 * devices with exactly one of each for now.

	 */

	list_for_each_entry(entity, &dev->entities, list) {

		if (UVC_ENTITY_IS_ITERM(entity)) {

			if (iterm)

				return -EINVAL;

			iterm = entity;

		}

		if (UVC_ENTITY_IS_OTERM(entity)) {

			if (oterm)

				return -EINVAL;

			oterm = entity;

		}

	}

	if (iterm == NULL || oterm == NULL)

		return -EINVAL;

	/* Allocate the chain and fill it. */

	chain = uvc_alloc_chain(dev);

	if (chain == NULL)

		return -ENOMEM;

	if (uvc_scan_chain_entity(chain, oterm) < 0)

		goto error;

	prev = oterm;

	/*

	 * Add all Processing and Extension Units with two pads. The order

	 * doesn't matter much, use reverse list traversal to connect units in

	 * UVC descriptor order as we build the chain from output to input. This

	 * leads to units appearing in the order meant by the manufacturer for

	 * the cameras known to require this heuristic.

	 */

	list_for_each_entry_reverse(entity, &dev->entities, list) {

		if (entity->type != UVC_VC_PROCESSING_UNIT &&

		    entity->type != UVC_VC_EXTENSION_UNIT)

			continue;

		if (entity->num_pads != 2)

			continue;

		if (uvc_scan_chain_entity(chain, entity) < 0)

			goto error;

		prev->baSourceID[0] = entity->id;

		prev = entity;

	}

	if (uvc_scan_chain_entity(chain, iterm) < 0)

		goto error;

	prev->baSourceID[0] = iterm->id;

	list_add_tail(&chain->list, &dev->chains);

	uvc_trace(UVC_TRACE_PROBE,

		  "Found a video chain by fallback heuristic (%s).\n",

		  uvc_print_chain(chain));

	return 0;

error:

	kfree(chain);

	return -EINVAL;

}

/*

 * Scan the device for video chains and register video devices.

 *

		if (term->chain.next || term->chain.prev)

			continue;

		chain = kzalloc(sizeof(*chain), GFP_KERNEL);

		chain = uvc_alloc_chain(dev);

		if (chain == NULL)

			return -ENOMEM;

		INIT_LIST_HEAD(&chain->entities);

		mutex_init(&chain->ctrl_mutex);

		chain->dev = dev;

		v4l2_prio_init(&chain->prio);

		term->flags |= UVC_ENTITY_FLAG_DEFAULT;

		if (uvc_scan_chain(chain, term) < 0) {

		list_add_tail(&chain->list, &dev->chains);

	}

	if (list_empty(&dev->chains))

		uvc_scan_fallback(dev);

	if (list_empty(&dev->chains)) {

		uvc_printk(KERN_INFO, "No valid video chain found.\n");

		return -1;