[media] gspca_main: Allow switching from read to mmap / userptr mode

Some applications (xawtv, qv4l2) mix read and mmap calls. Allow switching
from read mode back to mmap mode (by doing a reqbufs).
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Jean-Francois Moine <moinejf@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/gspca/gspca.c

@@ -1497,6 +1497,7 @@ static int vidioc_reqbufs(struct file *file, void *priv,
 		return -ERESTARTSYS;
 
 	if (gspca_dev->memory != GSPCA_MEMORY_NO
+	    && gspca_dev->memory != GSPCA_MEMORY_READ
 	    && gspca_dev->memory != rb->memory) {
 		ret = -EBUSY;
 		goto out;
@@ -1525,6 +1526,9 @@ static int vidioc_reqbufs(struct file *file, void *priv,
 		gspca_stream_off(gspca_dev);
 		mutex_unlock(&gspca_dev->usb_lock);
 	}
+	/* Don't restart the stream when switching from read to mmap mode */
+	if (gspca_dev->memory == GSPCA_MEMORY_READ)
+		streaming = 0;
 
 	/* free the previous allocated buffers, if any */
 	if (gspca_dev->nframes != 0)