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

Xu Yang posted 4 patches 1 month ago
There is a newer version of this series
[PATCH 2/4] usb: gadget: uvc: fix interval_duration calculation
Posted by Xu Yang 1 month ago 
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
Re: [PATCH 2/4] usb: gadget: uvc: fix interval_duration calculation
Posted by Frank Li 1 month ago 
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 2/4] usb: gadget: uvc: fix interval_duration calculation
Posted by Xu Yang 3 weeks, 6 days ago 
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

Patchew 2.1-devel-b67e4c2

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