uvcvideo: uvc_scan_fallback() for webcams with broken chain

commit e950267ab802c8558f1100eafd4087fd039ad634 upstream.

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)

Signed-off-by: Henrik Ingo <henrik.ingo@avoinelama.fi>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 363cdbf4ac8d8aa5f57072fcb2ae714dd5d5996b..5422093d135ccfbaf4ffac492417a956133dad6c 100644 (file)
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -1533,6 +1533,114 @@ static const char *uvc_print_chain(struct uvc_video_chain *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.
  *
@@ -1555,15 +1663,10 @@ static int uvc_scan_device(struct uvc_device *dev)
                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) {
@@ -1577,6 +1680,9 @@ static int uvc_scan_device(struct uvc_device *dev)
                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;