[PATCH 0/4] Some fix patches for uvc gadget function

[PATCH 0/4] Some fix patches for uvc gadget function

[Xu Yang]

Recenly when test uvc gadget function I find some YUYV pixel format
720p and 1080p stream can't output normally. However, small resulution
and MJPEG format stream works fine. The first patch#1 is to fix the issue.

Patch#2 and #3 are small fix or improvement.

For patch#4: it's a workaround for a long-term issue in videobuf2. With
it, many device can work well and not solely based on the SG allocation
method.

Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
Xu Yang (4):
      usb: gadget: uvc: fix req_payload_size calculation
      usb: gadget: uvc: fix interval_duration calculation
      usb: gadget: uvc: improve error handling in uvcg_video_init()
      usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

 drivers/usb/gadget/function/f_uvc.c     |  4 ++++
 drivers/usb/gadget/function/uvc.h       |  3 ++-
 drivers/usb/gadget/function/uvc_queue.c | 23 +++++++++++++++++++----
 drivers/usb/gadget/function/uvc_video.c | 14 +++++++-------
 4 files changed, 32 insertions(+), 12 deletions(-)
---
base-commit: 56a512a9b4107079f68701e7d55da8507eb963d9
change-id: 20260108-uvc-gadget-fix-patch-aa5996332bb5

Best regards,
-- 
Xu Yang <xu.yang_2@nxp.com>

[PATCH 1/4] usb: gadget: uvc: fix req_payload_size calculation

[Xu Yang]

Current req_payload_size calculation has 2 issue:

(1) When the first time calculate req_payload_size for all the buffers,
    reqs_per_frame = 0 will be the divisor of DIV_ROUND_UP(). So
    the result is undefined.
    This happens because VIDIOC_STREAMON is always executed after
    VIDIOC_QBUF. So video->reqs_per_frame will be 0 until VIDIOC_STREAMON
    is run.

(2) The buf->req_payload_size may be bigger than max_req_size.

    Take YUYV pixel format as example:
    If bInterval = 1, video->interval = 666666, high-speed:
    video->reqs_per_frame = 666666 / 1250 = 534
     720p: buf->req_payload_size = 1843200 / 534 = 3452
    1080p: buf->req_payload_size = 4147200 / 534 = 7766

    Based on such req_payload_size, the controller can't run normally.

To fix above issue, assign max_req_size to buf->req_payload_size when
video->reqs_per_frame = 0. And limit buf->req_payload_size to
video->req_size if it's large than video->req_size. Since max_req_size
is used at many place, add it to struct uvc_video and set the value once
endpoint is enabled.

Fixes: 98ad03291560 ("usb: gadget: uvc: set req_length based on payload by nreqs instead of req_size")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
 drivers/usb/gadget/function/f_uvc.c     |  4 ++++
 drivers/usb/gadget/function/uvc.h       |  1 +
 drivers/usb/gadget/function/uvc_queue.c | 15 +++++++++++----
 drivers/usb/gadget/function/uvc_video.c |  4 +---
 4 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
index aa6ab666741a9518690995ccdc04e742b4359a0e..a96476507d2fdf4eb0817f3aac09b7ee08df593a 100644
--- a/drivers/usb/gadget/function/f_uvc.c
+++ b/drivers/usb/gadget/function/f_uvc.c
@@ -362,6 +362,10 @@ uvc_function_set_alt(struct usb_function *f, unsigned interface, unsigned alt)
 			return ret;
 		usb_ep_enable(uvc->video.ep);
 
+		uvc->video.max_req_size = uvc->video.ep->maxpacket
+			* max_t(unsigned int, uvc->video.ep->maxburst, 1)
+			* (uvc->video.ep->mult);
+
 		memset(&v4l2_event, 0, sizeof(v4l2_event));
 		v4l2_event.type = UVC_EVENT_STREAMON;
 		v4l2_event_queue(&uvc->vdev, &v4l2_event);
diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index 9e79cbe50715791a7f7ddd3bc20e9a28d221db61..b3f88670bff801a43d084646974602e5995bb192 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -117,6 +117,7 @@ struct uvc_video {
 	/* Requests */
 	bool is_enabled; /* tracks whether video stream is enabled */
 	unsigned int req_size;
+	unsigned int max_req_size;
 	struct list_head ureqs; /* all uvc_requests allocated by uvc_video */
 
 	/* USB requests that the video pump thread can encode into */
diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
index 9a1bbd79ff5af945bdd5dcf0c1cb1b6dbdc12a9c..21d80322cb6148ed87eb77f453a1f1644e4923ae 100644
--- a/drivers/usb/gadget/function/uvc_queue.c
+++ b/drivers/usb/gadget/function/uvc_queue.c
@@ -86,10 +86,17 @@ static int uvc_buffer_prepare(struct vb2_buffer *vb)
 		buf->bytesused = 0;
 	} else {
 		buf->bytesused = vb2_get_plane_payload(vb, 0);
-		buf->req_payload_size =
-			  DIV_ROUND_UP(buf->bytesused +
-				       (video->reqs_per_frame * UVCG_REQUEST_HEADER_LEN),
-				       video->reqs_per_frame);
+
+		if (video->reqs_per_frame != 0)	{
+			buf->req_payload_size =
+				DIV_ROUND_UP(buf->bytesused +
+					(video->reqs_per_frame * UVCG_REQUEST_HEADER_LEN),
+					video->reqs_per_frame);
+			if (buf->req_payload_size > video->req_size)
+				buf->req_payload_size = video->req_size;
+		} else {
+			buf->req_payload_size = video->max_req_size;
+		}
 	}
 
 	return 0;
diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index fb77b0b21790178751d36a23f07d5b1efff5c25f..1c0672f707e4e5f29c937a1868f0400aad62e5cb 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -503,9 +503,7 @@ uvc_video_prep_requests(struct uvc_video *video)
 	unsigned int max_req_size, req_size, header_size;
 	unsigned int nreq;
 
-	max_req_size = video->ep->maxpacket
-		 * max_t(unsigned int, video->ep->maxburst, 1)
-		 * (video->ep->mult);
+	max_req_size = video->max_req_size;
 
 	if (!usb_endpoint_xfer_isoc(video->ep->desc)) {
 		video->req_size = max_req_size;

-- 
2.34.1

[PATCH 2/4] usb: gadget: uvc: fix interval_duration calculation

[Xu Yang]

According to USB specification:

  For full-/high-speed isochronous endpoints, the bInterval value is
  used as the exponent for a 2^(bInterval-1) value.

To correctly convert bInterval as interval_duration:
  interval_duration = 2^(bInterval-1) * frame_interval

Because the unit of video->interval is 100ns, add a comment info to
make it clear.

Fixes: 48dbe731171e ("usb: gadget: uvc: set req_size and n_requests based on the frame interval")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
 drivers/usb/gadget/function/uvc.h       | 2 +-
 drivers/usb/gadget/function/uvc_video.c | 7 +++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index b3f88670bff801a43d084646974602e5995bb192..676419a049762f9eb59e1ac68b19fa34f153b793 100644
--- a/drivers/usb/gadget/function/uvc.h
+++ b/drivers/usb/gadget/function/uvc.h
@@ -107,7 +107,7 @@ struct uvc_video {
 	unsigned int width;
 	unsigned int height;
 	unsigned int imagesize;
-	unsigned int interval;
+	unsigned int interval;	/* in 100ns units */
 	struct mutex mutex;	/* protects frame parameters */
 
 	unsigned int uvc_num_requests;
diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index 1c0672f707e4e5f29c937a1868f0400aad62e5cb..b1c5c1d3e9390c82cc84e736a7f288626ee69d51 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -499,7 +499,7 @@ uvc_video_prep_requests(struct uvc_video *video)
 {
 	struct uvc_device *uvc = container_of(video, struct uvc_device, video);
 	struct usb_composite_dev *cdev = uvc->func.config->cdev;
-	unsigned int interval_duration = video->ep->desc->bInterval * 1250;
+	unsigned int interval_duration;
 	unsigned int max_req_size, req_size, header_size;
 	unsigned int nreq;
 
@@ -513,8 +513,11 @@ uvc_video_prep_requests(struct uvc_video *video)
 		return;
 	}
 
+	interval_duration = int_pow(2, video->ep->desc->bInterval - 1);
 	if (cdev->gadget->speed < USB_SPEED_HIGH)
-		interval_duration = video->ep->desc->bInterval * 10000;
+		interval_duration *= 10000;
+	else
+		interval_duration *= 1250;
 
 	nreq = DIV_ROUND_UP(video->interval, interval_duration);
 

-- 
2.34.1

[PATCH 3/4] usb: gadget: uvc: improve error handling in uvcg_video_init()

[Xu Yang]

Let uvcg_video_init() return correct code so that error can be handled
correctly.

Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
 drivers/usb/gadget/function/uvc_video.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index b1c5c1d3e9390c82cc84e736a7f288626ee69d51..ede300190f591d39e306aecb565c614cdff5e664 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -838,7 +838,6 @@ int uvcg_video_init(struct uvc_video *video, struct uvc_device *uvc)
 	video->interval = 666666;
 
 	/* Initialize the video buffers queue. */
-	uvcg_queue_init(&video->queue, uvc->v4l2_dev.dev->parent,
+	return uvcg_queue_init(&video->queue, uvc->v4l2_dev.dev->parent,
 			V4L2_BUF_TYPE_VIDEO_OUTPUT, &video->mutex);
-	return 0;
 }

-- 
2.34.1

[PATCH 4/4] usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

[Xu Yang]

Based on the reality[1][2] that vb2_dma_sg_alloc() can't alloc buffer with
device DMA limits, those device will always get below error: "swiotlb
buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)"
and the uvc gadget function can't work at all.

The videobuf2-dma-sg.c driver doesn't has a formal improve about this issue
till now. To workaround the issue, lets retry vb2_reqbufs() with
vb_vmalloc_memops if it fails to allocate buffer with vb2_dma_sg_memops.

Link[1]: https://lore.kernel.org/linux-media/20230828075420.2009568-1-anle.pan@nxp.com/
Link[2]: https://lore.kernel.org/linux-media/20230914145812.12851-1-hui.fang@nxp.com/
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
---
 drivers/usb/gadget/function/uvc_queue.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
index 21d80322cb6148ed87eb77f453a1f1644e4923ae..586e5524c171f115d98af5dda43fb800466f46d2 100644
--- a/drivers/usb/gadget/function/uvc_queue.c
+++ b/drivers/usb/gadget/function/uvc_queue.c
@@ -182,7 +182,15 @@ int uvcg_alloc_buffers(struct uvc_video_queue *queue,
 {
 	int ret;
 
+retry:
 	ret = vb2_reqbufs(&queue->queue, rb);
+	if (ret < 0 && queue->use_sg) {
+		uvc_trace(UVC_TRACE_IOCTL,
+			  "failed to alloc buffer with sg enabled, try non-sg mode\n");
+		queue->use_sg = 0;
+		queue->queue.mem_ops = &vb2_vmalloc_memops;
+		goto retry;
+	}
 
 	return ret ? ret : rb->count;
 }

-- 
2.34.1

Re: [PATCH 1/4] usb: gadget: uvc: fix req_payload_size calculation

[Frank Li]

On Thu, Jan 08, 2026 at 03:43:02PM +0800, Xu Yang wrote:
> Current req_payload_size calculation has 2 issue:
>
> (1) When the first time calculate req_payload_size for all the buffers,
>     reqs_per_frame = 0 will be the divisor of DIV_ROUND_UP(). So
>     the result is undefined.
>     This happens because VIDIOC_STREAMON is always executed after
>     VIDIOC_QBUF. So video->reqs_per_frame will be 0 until VIDIOC_STREAMON
>     is run.
>
> (2) The buf->req_payload_size may be bigger than max_req_size.
>
>     Take YUYV pixel format as example:
>     If bInterval = 1, video->interval = 666666, high-speed:
>     video->reqs_per_frame = 666666 / 1250 = 534
>      720p: buf->req_payload_size = 1843200 / 534 = 3452
>     1080p: buf->req_payload_size = 4147200 / 534 = 7766
>
>     Based on such req_payload_size, the controller can't run normally.
>
> To fix above issue, assign max_req_size to buf->req_payload_size when
> video->reqs_per_frame = 0. And limit buf->req_payload_size to
> video->req_size if it's large than video->req_size. Since max_req_size
> is used at many place, add it to struct uvc_video and set the value once
> endpoint is enabled.
>
> Fixes: 98ad03291560 ("usb: gadget: uvc: set req_length based on payload by nreqs instead of req_size")
> Cc: stable@vger.kernel.org
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>

Reviewed-by: Frank Li <Frank.Li@nxp.com>

> ---
>  drivers/usb/gadget/function/f_uvc.c     |  4 ++++
>  drivers/usb/gadget/function/uvc.h       |  1 +
>  drivers/usb/gadget/function/uvc_queue.c | 15 +++++++++++----
>  drivers/usb/gadget/function/uvc_video.c |  4 +---
>  4 files changed, 17 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_uvc.c b/drivers/usb/gadget/function/f_uvc.c
> index aa6ab666741a9518690995ccdc04e742b4359a0e..a96476507d2fdf4eb0817f3aac09b7ee08df593a 100644
> --- a/drivers/usb/gadget/function/f_uvc.c
> +++ b/drivers/usb/gadget/function/f_uvc.c
> @@ -362,6 +362,10 @@ uvc_function_set_alt(struct usb_function *f, unsigned interface, unsigned alt)
>  			return ret;
>  		usb_ep_enable(uvc->video.ep);
>
> +		uvc->video.max_req_size = uvc->video.ep->maxpacket
> +			* max_t(unsigned int, uvc->video.ep->maxburst, 1)
> +			* (uvc->video.ep->mult);
> +
>  		memset(&v4l2_event, 0, sizeof(v4l2_event));
>  		v4l2_event.type = UVC_EVENT_STREAMON;
>  		v4l2_event_queue(&uvc->vdev, &v4l2_event);
> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> index 9e79cbe50715791a7f7ddd3bc20e9a28d221db61..b3f88670bff801a43d084646974602e5995bb192 100644
> --- a/drivers/usb/gadget/function/uvc.h
> +++ b/drivers/usb/gadget/function/uvc.h
> @@ -117,6 +117,7 @@ struct uvc_video {
>  	/* Requests */
>  	bool is_enabled; /* tracks whether video stream is enabled */
>  	unsigned int req_size;
> +	unsigned int max_req_size;
>  	struct list_head ureqs; /* all uvc_requests allocated by uvc_video */
>
>  	/* USB requests that the video pump thread can encode into */
> diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> index 9a1bbd79ff5af945bdd5dcf0c1cb1b6dbdc12a9c..21d80322cb6148ed87eb77f453a1f1644e4923ae 100644
> --- a/drivers/usb/gadget/function/uvc_queue.c
> +++ b/drivers/usb/gadget/function/uvc_queue.c
> @@ -86,10 +86,17 @@ static int uvc_buffer_prepare(struct vb2_buffer *vb)
>  		buf->bytesused = 0;
>  	} else {
>  		buf->bytesused = vb2_get_plane_payload(vb, 0);
> -		buf->req_payload_size =
> -			  DIV_ROUND_UP(buf->bytesused +
> -				       (video->reqs_per_frame * UVCG_REQUEST_HEADER_LEN),
> -				       video->reqs_per_frame);
> +
> +		if (video->reqs_per_frame != 0)	{
> +			buf->req_payload_size =
> +				DIV_ROUND_UP(buf->bytesused +
> +					(video->reqs_per_frame * UVCG_REQUEST_HEADER_LEN),
> +					video->reqs_per_frame);
> +			if (buf->req_payload_size > video->req_size)
> +				buf->req_payload_size = video->req_size;
> +		} else {
> +			buf->req_payload_size = video->max_req_size;
> +		}
>  	}
>
>  	return 0;
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index fb77b0b21790178751d36a23f07d5b1efff5c25f..1c0672f707e4e5f29c937a1868f0400aad62e5cb 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -503,9 +503,7 @@ uvc_video_prep_requests(struct uvc_video *video)
>  	unsigned int max_req_size, req_size, header_size;
>  	unsigned int nreq;
>
> -	max_req_size = video->ep->maxpacket
> -		 * max_t(unsigned int, video->ep->maxburst, 1)
> -		 * (video->ep->mult);
> +	max_req_size = video->max_req_size;
>
>  	if (!usb_endpoint_xfer_isoc(video->ep->desc)) {
>  		video->req_size = max_req_size;
>
> --
> 2.34.1
>

Re: [PATCH 2/4] usb: gadget: uvc: fix interval_duration calculation

[Frank Li]

On Thu, Jan 08, 2026 at 03:43:03PM +0800, Xu Yang wrote:
> According to USB specification:
>
>   For full-/high-speed isochronous endpoints, the bInterval value is
>   used as the exponent for a 2^(bInterval-1) value.
>
> To correctly convert bInterval as interval_duration:
>   interval_duration = 2^(bInterval-1) * frame_interval
>
> Because the unit of video->interval is 100ns, add a comment info to
> make it clear.
>
> Fixes: 48dbe731171e ("usb: gadget: uvc: set req_size and n_requests based on the frame interval")
> Cc: stable@vger.kernel.org
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> ---
>  drivers/usb/gadget/function/uvc.h       | 2 +-
>  drivers/usb/gadget/function/uvc_video.c | 7 +++++--
>  2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> index b3f88670bff801a43d084646974602e5995bb192..676419a049762f9eb59e1ac68b19fa34f153b793 100644
> --- a/drivers/usb/gadget/function/uvc.h
> +++ b/drivers/usb/gadget/function/uvc.h
> @@ -107,7 +107,7 @@ struct uvc_video {
>  	unsigned int width;
>  	unsigned int height;
>  	unsigned int imagesize;
> -	unsigned int interval;
> +	unsigned int interval;	/* in 100ns units */
>  	struct mutex mutex;	/* protects frame parameters */
>
>  	unsigned int uvc_num_requests;
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index 1c0672f707e4e5f29c937a1868f0400aad62e5cb..b1c5c1d3e9390c82cc84e736a7f288626ee69d51 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -499,7 +499,7 @@ uvc_video_prep_requests(struct uvc_video *video)
>  {
>  	struct uvc_device *uvc = container_of(video, struct uvc_device, video);
>  	struct usb_composite_dev *cdev = uvc->func.config->cdev;
> -	unsigned int interval_duration = video->ep->desc->bInterval * 1250;
> +	unsigned int interval_duration;
>  	unsigned int max_req_size, req_size, header_size;
>  	unsigned int nreq;
>
> @@ -513,8 +513,11 @@ uvc_video_prep_requests(struct uvc_video *video)
>  		return;
>  	}
>
> +	interval_duration = int_pow(2, video->ep->desc->bInterval - 1);

2 << (video->ep->desc->bInterval - 1) or BIT(video->ep->desc->bInterval - 1);

int_pow() use while loop. slice better.

Reviewed-by: Frank Li <Frank.Li@nxp.com>

Frank

>  	if (cdev->gadget->speed < USB_SPEED_HIGH)
> -		interval_duration = video->ep->desc->bInterval * 10000;
> +		interval_duration *= 10000;
> +	else
> +		interval_duration *= 1250;
>
>  	nreq = DIV_ROUND_UP(video->interval, interval_duration);
>
>
> --
> 2.34.1
>

Re: [PATCH 3/4] usb: gadget: uvc: improve error handling in uvcg_video_init()

[Frank Li]

On Thu, Jan 08, 2026 at 03:43:04PM +0800, Xu Yang wrote:
> Let uvcg_video_init() return correct code so that error can be handled
> correctly.

usb: gadget: uvc: Return error from uvcg_queue_init()

uvcg_queue_init() may fail, but its return value is currently ignored.
Propagate the error code from uvcg_queue_init() to correctly report
initialization failures.

Frank
>
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> ---
>  drivers/usb/gadget/function/uvc_video.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index b1c5c1d3e9390c82cc84e736a7f288626ee69d51..ede300190f591d39e306aecb565c614cdff5e664 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -838,7 +838,6 @@ int uvcg_video_init(struct uvc_video *video, struct uvc_device *uvc)
>  	video->interval = 666666;
>
>  	/* Initialize the video buffers queue. */
> -	uvcg_queue_init(&video->queue, uvc->v4l2_dev.dev->parent,
> +	return uvcg_queue_init(&video->queue, uvc->v4l2_dev.dev->parent,
>  			V4L2_BUF_TYPE_VIDEO_OUTPUT, &video->mutex);
> -	return 0;
>  }
>
> --
> 2.34.1
>

Re: [PATCH 4/4] usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

[Frank Li]

On Thu, Jan 08, 2026 at 03:43:05PM +0800, Xu Yang wrote:
> Based on the reality[1][2] that vb2_dma_sg_alloc() can't alloc buffer with
> device DMA limits, those device will always get below error: "swiotlb
> buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)"
> and the uvc gadget function can't work at all.
>
> The videobuf2-dma-sg.c driver doesn't has a formal improve about this issue
> till now. To workaround the issue, lets retry vb2_reqbufs() with
> vb_vmalloc_memops if it fails to allocate buffer with vb2_dma_sg_memops.
>
> Link[1]: https://lore.kernel.org/linux-media/20230828075420.2009568-1-anle.pan@nxp.com/
> Link[2]: https://lore.kernel.org/linux-media/20230914145812.12851-1-hui.fang@nxp.com/
> Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> ---
>  drivers/usb/gadget/function/uvc_queue.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> index 21d80322cb6148ed87eb77f453a1f1644e4923ae..586e5524c171f115d98af5dda43fb800466f46d2 100644
> --- a/drivers/usb/gadget/function/uvc_queue.c
> +++ b/drivers/usb/gadget/function/uvc_queue.c
> @@ -182,7 +182,15 @@ int uvcg_alloc_buffers(struct uvc_video_queue *queue,
>  {
>  	int ret;
>
> +retry:
>  	ret = vb2_reqbufs(&queue->queue, rb);
> +	if (ret < 0 && queue->use_sg) {
> +		uvc_trace(UVC_TRACE_IOCTL,
> +			  "failed to alloc buffer with sg enabled, try non-sg mode\n");
> +		queue->use_sg = 0;
> +		queue->queue.mem_ops = &vb2_vmalloc_memops;

How it work if dma_sg_alloc() failure,  vmalloc success, follow dma_map()
should be failure for vmalloc()

Frank

> +		goto retry;
> +	}
>
>  	return ret ? ret : rb->count;
>  }
>
> --
> 2.34.1
>

Re: [PATCH 2/4] usb: gadget: uvc: fix interval_duration calculation

[Xu Yang]

On Thu, Jan 08, 2026 at 11:04:19AM -0500, Frank Li wrote:
> On Thu, Jan 08, 2026 at 03:43:03PM +0800, Xu Yang wrote:
> > According to USB specification:
> >
> >   For full-/high-speed isochronous endpoints, the bInterval value is
> >   used as the exponent for a 2^(bInterval-1) value.
> >
> > To correctly convert bInterval as interval_duration:
> >   interval_duration = 2^(bInterval-1) * frame_interval
> >
> > Because the unit of video->interval is 100ns, add a comment info to
> > make it clear.
> >
> > Fixes: 48dbe731171e ("usb: gadget: uvc: set req_size and n_requests based on the frame interval")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> > ---
> >  drivers/usb/gadget/function/uvc.h       | 2 +-
> >  drivers/usb/gadget/function/uvc_video.c | 7 +++++--
> >  2 files changed, 6 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> > index b3f88670bff801a43d084646974602e5995bb192..676419a049762f9eb59e1ac68b19fa34f153b793 100644
> > --- a/drivers/usb/gadget/function/uvc.h
> > +++ b/drivers/usb/gadget/function/uvc.h
> > @@ -107,7 +107,7 @@ struct uvc_video {
> >  	unsigned int width;
> >  	unsigned int height;
> >  	unsigned int imagesize;
> > -	unsigned int interval;
> > +	unsigned int interval;	/* in 100ns units */
> >  	struct mutex mutex;	/* protects frame parameters */
> >
> >  	unsigned int uvc_num_requests;
> > diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> > index 1c0672f707e4e5f29c937a1868f0400aad62e5cb..b1c5c1d3e9390c82cc84e736a7f288626ee69d51 100644
> > --- a/drivers/usb/gadget/function/uvc_video.c
> > +++ b/drivers/usb/gadget/function/uvc_video.c
> > @@ -499,7 +499,7 @@ uvc_video_prep_requests(struct uvc_video *video)
> >  {
> >  	struct uvc_device *uvc = container_of(video, struct uvc_device, video);
> >  	struct usb_composite_dev *cdev = uvc->func.config->cdev;
> > -	unsigned int interval_duration = video->ep->desc->bInterval * 1250;
> > +	unsigned int interval_duration;
> >  	unsigned int max_req_size, req_size, header_size;
> >  	unsigned int nreq;
> >
> > @@ -513,8 +513,11 @@ uvc_video_prep_requests(struct uvc_video *video)
> >  		return;
> >  	}
> >
> > +	interval_duration = int_pow(2, video->ep->desc->bInterval - 1);
> 
> 2 << (video->ep->desc->bInterval - 1) or BIT(video->ep->desc->bInterval - 1);
> 
> int_pow() use while loop. slice better.
> 
> Reviewed-by: Frank Li <Frank.Li@nxp.com>

Good suggestion!

Thanks,
Xu Yang

Re: [PATCH 3/4] usb: gadget: uvc: improve error handling in uvcg_video_init()

[Xu Yang]

On Thu, Jan 08, 2026 at 11:08:25AM -0500, Frank Li wrote:
> On Thu, Jan 08, 2026 at 03:43:04PM +0800, Xu Yang wrote:
> > Let uvcg_video_init() return correct code so that error can be handled
> > correctly.
> 
> usb: gadget: uvc: Return error from uvcg_queue_init()
> 
> uvcg_queue_init() may fail, but its return value is currently ignored.
> Propagate the error code from uvcg_queue_init() to correctly report
> initialization failures.

Ok. Thank you for provide a better commit message.

Thanks,
Xu Yang

Re: [PATCH 4/4] usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

[Xu Yang]

On Thu, Jan 08, 2026 at 11:16:08AM -0500, Frank Li wrote:
> On Thu, Jan 08, 2026 at 03:43:05PM +0800, Xu Yang wrote:
> > Based on the reality[1][2] that vb2_dma_sg_alloc() can't alloc buffer with
> > device DMA limits, those device will always get below error: "swiotlb
> > buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)"
> > and the uvc gadget function can't work at all.
> >
> > The videobuf2-dma-sg.c driver doesn't has a formal improve about this issue
> > till now. To workaround the issue, lets retry vb2_reqbufs() with
> > vb_vmalloc_memops if it fails to allocate buffer with vb2_dma_sg_memops.
> >
> > Link[1]: https://lore.kernel.org/linux-media/20230828075420.2009568-1-anle.pan@nxp.com/
> > Link[2]: https://lore.kernel.org/linux-media/20230914145812.12851-1-hui.fang@nxp.com/
> > Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> > ---
> >  drivers/usb/gadget/function/uvc_queue.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> > index 21d80322cb6148ed87eb77f453a1f1644e4923ae..586e5524c171f115d98af5dda43fb800466f46d2 100644
> > --- a/drivers/usb/gadget/function/uvc_queue.c
> > +++ b/drivers/usb/gadget/function/uvc_queue.c
> > @@ -182,7 +182,15 @@ int uvcg_alloc_buffers(struct uvc_video_queue *queue,
> >  {
> >  	int ret;
> >
> > +retry:
> >  	ret = vb2_reqbufs(&queue->queue, rb);
> > +	if (ret < 0 && queue->use_sg) {
> > +		uvc_trace(UVC_TRACE_IOCTL,
> > +			  "failed to alloc buffer with sg enabled, try non-sg mode\n");
> > +		queue->use_sg = 0;
> > +		queue->queue.mem_ops = &vb2_vmalloc_memops;
> 
> How it work if dma_sg_alloc() failure,  vmalloc success, follow dma_map()
> should be failure for vmalloc()

The point is the videobuf2 subsystem doesn't do dma_map() on vmalloc returned big buffer,
however, it do it for dma_sg returned buffer. 

If use vmalloced buffer, UVC gadget already allocate some small buffer for each usb_request
to do dma transfer, so uvc driver will memcopy data from big buffer to small buffer.

If use dma-sg-ed buffer, uvc driver won't memcopy data, instead it will use part of sg
buffer each time.

Then USB system will do usb_gadget_map_request() again before each transfer.

Thanks,
Xu Yang

> 
> Frank
> 
> > +		goto retry;
> > +	}
> >
> >  	return ret ? ret : rb->count;
> >  }
> >
> > --
> > 2.34.1
> >

Re: [PATCH 4/4] usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

[Frank Li]

On Mon, Jan 12, 2026 at 06:05:40PM +0800, Xu Yang wrote:
> On Thu, Jan 08, 2026 at 11:16:08AM -0500, Frank Li wrote:
> > On Thu, Jan 08, 2026 at 03:43:05PM +0800, Xu Yang wrote:
> > > Based on the reality[1][2] that vb2_dma_sg_alloc() can't alloc buffer with
> > > device DMA limits, those device will always get below error: "swiotlb
> > > buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)"
> > > and the uvc gadget function can't work at all.
> > >
> > > The videobuf2-dma-sg.c driver doesn't has a formal improve about this issue
> > > till now. To workaround the issue, lets retry vb2_reqbufs() with
> > > vb_vmalloc_memops if it fails to allocate buffer with vb2_dma_sg_memops.
> > >
> > > Link[1]: https://lore.kernel.org/linux-media/20230828075420.2009568-1-anle.pan@nxp.com/
> > > Link[2]: https://lore.kernel.org/linux-media/20230914145812.12851-1-hui.fang@nxp.com/
> > > Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
> > > ---
> > >  drivers/usb/gadget/function/uvc_queue.c | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> > > index 21d80322cb6148ed87eb77f453a1f1644e4923ae..586e5524c171f115d98af5dda43fb800466f46d2 100644
> > > --- a/drivers/usb/gadget/function/uvc_queue.c
> > > +++ b/drivers/usb/gadget/function/uvc_queue.c
> > > @@ -182,7 +182,15 @@ int uvcg_alloc_buffers(struct uvc_video_queue *queue,
> > >  {
> > >  	int ret;
> > >
> > > +retry:
> > >  	ret = vb2_reqbufs(&queue->queue, rb);
> > > +	if (ret < 0 && queue->use_sg) {
> > > +		uvc_trace(UVC_TRACE_IOCTL,
> > > +			  "failed to alloc buffer with sg enabled, try non-sg mode\n");
> > > +		queue->use_sg = 0;
> > > +		queue->queue.mem_ops = &vb2_vmalloc_memops;
> >
> > How it work if dma_sg_alloc() failure,  vmalloc success, follow dma_map()
> > should be failure for vmalloc()
>
> The point is the videobuf2 subsystem doesn't do dma_map() on vmalloc returned big buffer,
> however, it do it for dma_sg returned buffer.
>
> If use vmalloced buffer, UVC gadget already allocate some small buffer for each usb_request
> to do dma transfer, so uvc driver will memcopy data from big buffer to small buffer.

Need add such information to commit message.

Frank

>
> If use dma-sg-ed buffer, uvc driver won't memcopy data, instead it will use part of sg
> buffer each time.
>
> Then USB system will do usb_gadget_map_request() again before each transfer.
>
> Thanks,
> Xu Yang
>
> >
> > Frank
> >
> > > +		goto retry;
> > > +	}
> > >
> > >  	return ret ? ret : rb->count;
> > >  }
> > >
> > > --
> > > 2.34.1
> > >