usb: gadget: uvc: fix req_payload_size calculation

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: 98ad032 ("usb: gadget: uvc: set req_length based on payload by nreqs instead of req_size")
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-v2-1-62950ef5bcb5@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Xu Yang

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);

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 */

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;

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;