[PATCH] usb: gadget: uvc: limit isoc_sg to super speed gadgets

[Michael Grzeschik <m.grzeschik@pengutronix.de>]

The overhead of preparing sg data is high for transfers with limited
payload. When transferring isoc over high-speed usb the maximum payload
is rather small which is a good argument no to use sg. This patch is
changing the uvc_video_encode_isoc_sg encode function only to be used
for super speed gadgets.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
---
 drivers/usb/gadget/function/uvc_video.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
index bb037fcc90e69e..5081eb3bc5484c 100644
--- a/drivers/usb/gadget/function/uvc_video.c
+++ b/drivers/usb/gadget/function/uvc_video.c
@@ -448,6 +448,9 @@ static void uvcg_video_pump(struct work_struct *work)
  */
 int uvcg_video_enable(struct uvc_video *video, int enable)
 {
+	struct uvc_device *uvc = video->uvc;
+	struct usb_composite_dev *cdev = uvc->func.config->cdev;
+	struct usb_gadget *gadget = cdev->gadget;
 	unsigned int i;
 	int ret;
 
@@ -479,9 +482,11 @@ int uvcg_video_enable(struct uvc_video *video, int enable)
 	if (video->max_payload_size) {
 		video->encode = uvc_video_encode_bulk;
 		video->payload_size = 0;
-	} else
-		video->encode = video->queue.use_sg ?
+	} else {
+		video->encode = (video->queue.use_sg &&
+				 !(gadget->speed <= USB_SPEED_HIGH)) ?
 			uvc_video_encode_isoc_sg : uvc_video_encode_isoc;
+	}
 
 	video->req_int_count = 0;
 
-- 
2.30.2