drm/udl: Ensure channel is selected before using the device.

Lift configuration command from udlfb. This appears to be essential for
at least a Rextron VCUD-60, without which no URB communication occurs.
Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1471904254-26545-1-git-send-email-jm@lentin.co.uk

drivers/gpu/drm/udl/udl_main.c

@@ -16,6 +16,8 @@
 /* -BULK_SIZE as per usb-skeleton. Can we get full page and avoid overhead? */
 #define BULK_SIZE 512
 
+#define NR_USB_REQUEST_CHANNEL 0x12
+
 #define MAX_TRANSFER (PAGE_SIZE*16 - BULK_SIZE)
 #define WRITES_IN_FLIGHT (4)
 #define MAX_VENDOR_DESCRIPTOR_SIZE 256
@@ -90,6 +92,26 @@ static int udl_parse_vendor_descriptor(struct drm_device *dev,
 	return true;
 }
 
+/*
+ * Need to ensure a channel is selected before submitting URBs
+ */
+static int udl_select_std_channel(struct udl_device *udl)
+{
+	int ret;
+	u8 set_def_chn[] = {0x57, 0xCD, 0xDC, 0xA7,
+			    0x1C, 0x88, 0x5E, 0x15,
+			    0x60, 0xFE, 0xC6, 0x97,
+			    0x16, 0x3D, 0x47, 0xF2};
+
+	ret = usb_control_msg(udl->udev,
+			      usb_sndctrlpipe(udl->udev, 0),
+			      NR_USB_REQUEST_CHANNEL,
+			      (USB_DIR_OUT | USB_TYPE_VENDOR), 0, 0,
+			      set_def_chn, sizeof(set_def_chn),
+			      USB_CTRL_SET_TIMEOUT);
+	return ret < 0 ? ret : 0;
+}
+
 static void udl_release_urb_work(struct work_struct *work)
 {
 	struct urb_node *unode = container_of(work, struct urb_node,
@@ -301,6 +323,9 @@ int udl_driver_load(struct drm_device *dev, unsigned long flags)
 		goto err;
 	}
 
+	if (udl_select_std_channel(udl))
+		DRM_ERROR("Selecting channel failed\n");
+
 	if (!udl_alloc_urb_list(dev, WRITES_IN_FLIGHT, MAX_TRANSFER)) {
 		DRM_ERROR("udl_alloc_urb_list failed\n");
 		goto err;