V4L/DVB (13829): uvcvideo: Fix alternate setting selection in isochronous mode

Unlike assumed by the driver, alternate settings are not sorted by
endpoint max packet size. Iterate over all alternate settings to find
the one with the smallest compatible max packet size.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_video.c

@@ -924,10 +924,8 @@ static int uvc_init_video_bulk(struct uvc_streaming *stream,
 static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
 {
 	struct usb_interface *intf = stream->intf;
-	struct usb_host_interface *alts;
-	struct usb_host_endpoint *ep = NULL;
-	int intfnum = stream->intfnum;
-	unsigned int bandwidth, psize, i;
+	struct usb_host_endpoint *ep;
+	unsigned int i;
 	int ret;
 
 	stream->last_fid = -1;
@@ -936,6 +934,12 @@ static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
 	stream->bulk.payload_size = 0;
 
 	if (intf->num_altsetting > 1) {
+		struct usb_host_endpoint *best_ep = NULL;
+		unsigned int best_psize = 3 * 1024;
+		unsigned int bandwidth;
+		unsigned int uninitialized_var(altsetting);
+		int intfnum = stream->intfnum;
+
 		/* Isochronous endpoint, select the alternate setting. */
 		bandwidth = stream->ctrl.dwMaxPayloadTransferSize;
 
@@ -949,6 +953,9 @@ static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
 		}
 
 		for (i = 0; i < intf->num_altsetting; ++i) {
+			struct usb_host_interface *alts;
+			unsigned int psize;
+
 			alts = &intf->altsetting[i];
 			ep = uvc_find_endpoint(alts,
 				stream->header.bEndpointAddress);
@@ -958,21 +965,27 @@ static int uvc_init_video(struct uvc_streaming *stream, gfp_t gfp_flags)
 			/* Check if the bandwidth is high enough. */
 			psize = le16_to_cpu(ep->desc.wMaxPacketSize);
 			psize = (psize & 0x07ff) * (1 + ((psize >> 11) & 3));
-			if (psize >= bandwidth)
-				break;
+			if (psize >= bandwidth && psize <= best_psize) {
+				altsetting = i;
+				best_psize = psize;
+				best_ep = ep;
+			}
 		}
 
-		if (i >= intf->num_altsetting) {
+		if (best_ep == NULL) {
 			uvc_trace(UVC_TRACE_VIDEO, "No fast enough alt setting "
 				"for requested bandwidth.\n");
 			return -EIO;
 		}
 
-		ret = usb_set_interface(stream->dev->udev, intfnum, i);
+		uvc_trace(UVC_TRACE_VIDEO, "Selecting alternate setting %u "
+			"(%u B/frame bandwidth).\n", altsetting, best_psize);
+
+		ret = usb_set_interface(stream->dev->udev, intfnum, altsetting);
 		if (ret < 0)
 			return ret;
 
-		ret = uvc_init_video_isoc(stream, ep, gfp_flags);
+		ret = uvc_init_video_isoc(stream, best_ep, gfp_flags);
 	} else {
 		/* Bulk endpoint, proceed to URB initialization. */
 		ep = uvc_find_endpoint(&intf->altsetting[0],