linux-kernel - Re: [PATCH v2] media: uvcvideo: Use heuristic to find stream entity

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Message-ID: <b282f6ef-fd91-44ea-bf51-187cf2c56fc6@kernel.org>
Date: Tue, 21 Oct 2025 18:07:49 +0200
From: Hans de Goede <hansg@...nel.org>
To: Ricardo Ribalda <ribalda@...omium.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 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
Subject: Re: [PATCH v2] media: uvcvideo: Use heuristic to find stream entity

Hi,

On 21-Oct-25 12:36, Ricardo Ribalda wrote:
> 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>

Thanks, patch looks good to me:

Reviewed-by: Hans de Goede <hansg@...nel.org>

Regards,

Hans



> ---
> 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]
> ---
> Changes in v2:
> - Fix : invalid reference to the index variable of the iterator.
> - Link to v1: https://lore.kernel.org/r/20251021-uvc-grandstream-v1-1-801e3d08b271@chromium.org
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index fb6afb8e84f00961f86fd8f840fba48d706d7a9a..ee4f54d6834962414979a046afc59c5036455124 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -167,13 +167,26 @@ 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;
> +	struct uvc_streaming *stream, *last_stream;
> +	unsigned int count = 0;
>  
>  	list_for_each_entry(stream, &dev->streams, list) {
> +		count += 1;
> +		last_stream = stream;
>  		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 last_stream;
> +	}
> +
>  	return NULL;
>  }
>  
> 
> ---
> base-commit: ea299a2164262ff787c9d33f46049acccd120672
> change-id: 20251021-uvc-grandstream-05ecf0288f62
> 
> Best regards,