usb: gadget: uvc: fix interval_duration calculation

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
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Link: https://patch.msgid.link/20260113-uvc-gadget-fix-patch-v2-2-62950ef5bcb5@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
index b3f88670bff801a43d084646974602e5995bb192..676419a049762f9eb59e1ac68b19fa34f153b793 100644 (file)
--- 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..9dc3af16e2f38957198bf579987f4324fc552c5d 100644 (file)
--- 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 = 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);