[PATCH 3.10 201/268] uvcvideo: uvc_scan_fallback() for webcams with broken chain

Willy Tarreau
2017-06-19T18:36:32Z

From: Henrik Ingo <henrik.ingo@avoinelama.fi>

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>
---
drivers/media/usb/uvc/uvc_driver.c | 118 +++++++++++++++++++++++++++++++++++--
1 file changed, 112 insertions(+), 6 deletions(-)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 363cdbf..5422093 100644
--- 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;
--
2.8.0.rc2.1.gbe9624a