linux-kernel - [PATCH] media: uvcvideo: Use heuristic to find stream entity

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Message-Id: <20251021-uvc-grandstream-v1-1-801e3d08b271@chromium.org>
Date: Tue, 21 Oct 2025 09:14:40 +0000
From: Ricardo Ribalda <ribalda@...omium.org>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Hans de Goede <hansg@...nel.org>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, 
 Hans Verkuil <hverkuil+cisco@...nel.org>, 
 Thadeu Lima de Souza Cascardo <cascardo@...lia.com>, 
 Angel4005 <ooara1337@...il.com>
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Ricardo Ribalda <ribalda@...omium.org>
Subject: [PATCH] media: uvcvideo: Use heuristic to find stream entity

Some devices, like the Grandstream GUV3100 webcam, have an invalid UVC
descriptor where multiple entities share the same ID, this is invalid
and makes it impossible to make a proper entity tree without heuristics.

We have recently introduced a change in the way that we handle invalid
entities that has caused a regression on broken devices.

Implement a new heuristic to handle these devices properly.

Reported-by: Angel4005 <ooara1337@...il.com>
Closes: https://lore.kernel.org/linux-media/CAOzBiVuS7ygUjjhCbyWg-KiNx+HFTYnqH5+GJhd6cYsNLT=DaA@mail.gmail.com/
Fixes: 0e2ee70291e6 ("media: uvcvideo: Mark invalid entities with id UVC_INVALID_ENTITY_ID")
Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
---
I have managed to get my hands into a Grandstream GUV3100 and
implemented a new heuristics. (Thanks Yunke and Hidenori!).

With this heuristics we can use this camera again (see the /dev/video0
in the topology).

I have tested this change in a 6.6 kernel. Because the notebook that I
used for testing has some issues running master. But for the purpose of
this change this test should work.

~ # media-ctl --print-topology
Media controller API version 6.6.99

Media device information
------------------------
driver          uvcvideo
model           GRANDSTREAM GUV3100: GRANDSTREA
serial
bus info        usb-0000:00:14.0-9
hw revision     0x409
driver version  6.6.99

Device topology
- entity 1: GRANDSTREAM GUV3100: GRANDSTREA (1 pad, 1 link)
            type Node subtype V4L flags 1
            device node name /dev/video0
        pad0: SINK
                <- "Extension 3":1 [ENABLED,IMMUTABLE]

- entity 4: GRANDSTREAM GUV3100: GRANDSTREA (0 pad, 0 link)
            type Node subtype V4L flags 0
            device node name /dev/video1

- entity 8: Extension 3 (2 pads, 2 links, 0 routes)
            type V4L2 subdev subtype Unknown flags 0
        pad0: SINK
                <- "Processing 2":1 [ENABLED,IMMUTABLE]
        pad1: SOURCE
                -> "GRANDSTREAM GUV3100: GRANDSTREA":0 [ENABLED,IMMUTABLE]

- entity 11: Processing 2 (2 pads, 3 links, 0 routes)
             type V4L2 subdev subtype Unknown flags 0
        pad0: SINK
                <- "Camera 1":0 [ENABLED,IMMUTABLE]
        pad1: SOURCE
                -> "Extension 3":0 [ENABLED,IMMUTABLE]
                -> "Extension 4":0 [ENABLED,IMMUTABLE]

- entity 14: Extension 4 (2 pads, 1 link, 0 routes)
             type V4L2 subdev subtype Unknown flags 0
        pad0: SINK
                <- "Processing 2":1 [ENABLED,IMMUTABLE]
        pad1: SOURCE

- entity 17: Camera 1 (1 pad, 1 link, 0 routes)
             type V4L2 subdev subtype Sensor flags 0
        pad0: SOURCE
                -> "Processing 2":0 [ENABLED,IMMUTABLE]
---
 drivers/media/usb/uvc/uvc_driver.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index fb6afb8e84f00961f86fd8f840fba48d706d7a9a..4a8712d2d663ab0c31a1586ed7da6fd42f3ad3cc 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -168,12 +168,24 @@ static struct uvc_entity *uvc_entity_by_reference(struct uvc_device *dev,
 static struct uvc_streaming *uvc_stream_by_id(struct uvc_device *dev, int id)
 {
 	struct uvc_streaming *stream;
+	unsigned int count = 0;
 
 	list_for_each_entry(stream, &dev->streams, list) {
+		count += 1;
 		if (stream->header.bTerminalLink == id)
 			return stream;
 	}
 
+	/*
+	 * If the streaming entity is referenced by an invalid ID, notify the
+	 * user and use heuristics to guess the correct entity.
+	 */
+	if (count == 1 && id == UVC_INVALID_ENTITY_ID) {
+		dev_warn(&dev->intf->dev,
+			 "UVC non compliance: Invalid USB header. The streaming entity has an invalid ID, guessing the correct one.");
+		return stream;
+	}
+
 	return NULL;
 }
 

---
base-commit: ea299a2164262ff787c9d33f46049acccd120672
change-id: 20251021-uvc-grandstream-05ecf0288f62

Best regards,
-- 
Ricardo Ribalda <ribalda@...omium.org>