[media] gspca: provide a mechanism to select a specific transfer endpoint

Currently gspca selects the first ISOC input endpoint as the input
transfer endpoint, however some devices can provide streams on endpoints
different then the first one, so some subdrivers (e.g. gspca_kinect) may
want to select a specific endpoint to use as a transfer endpoint.

Add an xfer_ep field to struct gspca_dev, and change alt_xfer() so that
it accepts a parameter which represents a specific endpoint address to
look for.

If a subdriver wants to specify a value for gspca_dev->xfer_ep it can do
that in its sd_config() callback.

Signed-off-by: Antonio Ospite <ao2@ao2.it>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/usb/gspca/gspca.c

@@ -603,10 +603,13 @@ static void gspca_stream_off(struct gspca_dev *gspca_dev)
 }
 
 /*
- * look for an input transfer endpoint in an alternate setting
+ * look for an input transfer endpoint in an alternate setting.
+ *
+ * If xfer_ep is invalid, return the first valid ep found, otherwise
+ * look for exactly the ep with address equal to xfer_ep.
  */
 static struct usb_host_endpoint *alt_xfer(struct usb_host_interface *alt,
-					  int xfer)
+					  int xfer, int xfer_ep)
 {
 	struct usb_host_endpoint *ep;
 	int i, attr;
@@ -616,7 +619,8 @@ static struct usb_host_endpoint *alt_xfer(struct usb_host_interface *alt,
 		attr = ep->desc.bmAttributes & USB_ENDPOINT_XFERTYPE_MASK;
 		if (attr == xfer
 		    && ep->desc.wMaxPacketSize != 0
-		    && usb_endpoint_dir_in(&ep->desc))
+		    && usb_endpoint_dir_in(&ep->desc)
+		    && (xfer_ep < 0 || ep->desc.bEndpointAddress == xfer_ep))
 			return ep;
 	}
 	return NULL;
@@ -689,7 +693,8 @@ static int build_isoc_ep_tb(struct gspca_dev *gspca_dev,
 		found = 0;
 		for (j = 0; j < nbalt; j++) {
 			ep = alt_xfer(&intf->altsetting[j],
-				      USB_ENDPOINT_XFER_ISOC);
+				      USB_ENDPOINT_XFER_ISOC,
+				      gspca_dev->xfer_ep);
 			if (ep == NULL)
 				continue;
 			if (ep->desc.bInterval == 0) {
@@ -862,7 +867,8 @@ static int gspca_init_transfer(struct gspca_dev *gspca_dev)
 	/* if bulk or the subdriver forced an altsetting, get the endpoint */
 	if (gspca_dev->alt != 0) {
 		gspca_dev->alt--;	/* (previous version compatibility) */
-		ep = alt_xfer(&intf->altsetting[gspca_dev->alt], xfer);
+		ep = alt_xfer(&intf->altsetting[gspca_dev->alt], xfer,
+			      gspca_dev->xfer_ep);
 		if (ep == NULL) {
 			pr_err("bad altsetting %d\n", gspca_dev->alt);
 			return -EIO;
@@ -904,7 +910,8 @@ static int gspca_init_transfer(struct gspca_dev *gspca_dev)
 		if (!gspca_dev->cam.no_urb_create) {
 			PDEBUG(D_STREAM, "init transfer alt %d", alt);
 			ret = create_urbs(gspca_dev,
-				alt_xfer(&intf->altsetting[alt], xfer));
+				alt_xfer(&intf->altsetting[alt], xfer,
+					 gspca_dev->xfer_ep));
 			if (ret < 0) {
 				destroy_urbs(gspca_dev);
 				goto out;
@@ -2030,6 +2037,7 @@ int gspca_dev_probe2(struct usb_interface *intf,
 	}
 	gspca_dev->dev = dev;
 	gspca_dev->iface = intf->cur_altsetting->desc.bInterfaceNumber;
+	gspca_dev->xfer_ep = -1;
 
 	/* check if any audio device */
 	if (dev->actconfig->desc.bNumInterfaces != 1) {

drivers/media/usb/gspca/gspca.h

@@ -205,6 +205,7 @@ struct gspca_dev {
 	char memory;			/* memory type (V4L2_MEMORY_xxx) */
 	__u8 iface;			/* USB interface number */
 	__u8 alt;			/* USB alternate setting */
+	int xfer_ep;			/* USB transfer endpoint address */
 	u8 audio;			/* presence of audio device */
 
 	/* (*) These variables are proteced by both usb_lock and queue_lock,