usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail

Based on the reality[1][2] that vb2_dma_sg_alloc() can't alloc buffer with
device DMA limits, those device will always get below error: "swiotlb
buffer is full (sz: 393216 bytes), total 65536 (slots), used 2358 (slots)"
and the uvc gadget function can't work at all.

The videobuf2-dma-sg.c driver doesn't has a formal improve about this issue
till now. For UVC gadget, the videobuf2 subsystem doesn't do dma_map() on
vmalloc returned big buffer when allocate the video buffers, however, it do
it for dma_sg returned buffer. So the issue happens for vb2_dma_sg_alloc().

To workaround the issue, lets retry vb2_reqbufs() with
vb_vmalloc_memops if it fails to allocate buffer with vb2_dma_sg_memops.
If use vmalloced buffer, UVC gadget will allocate some small buffers for
each usb_request to do dma transfer, then uvc driver will memcopy data
from big buffer to small buffer.

Link[1]: https://lore.kernel.org/linux-media/20230828075420.2009568-1-anle.pan@nxp.com/
Link[2]: https://lore.kernel.org/linux-media/20230914145812.12851-1-hui.fang@nxp.com/
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20260113-uvc-gadget-fix-patch-v2-4-62950ef5bcb5@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Xu Yang

drivers/usb/gadget/function/uvc_queue.c

@@ -182,7 +182,15 @@ int uvcg_alloc_buffers(struct uvc_video_queue *queue,
 {
 	int ret;
 
+retry:
 	ret = vb2_reqbufs(&queue->queue, rb);
+	if (ret < 0 && queue->use_sg) {
+		uvc_trace(UVC_TRACE_IOCTL,
+			  "failed to alloc buffer with sg enabled, try non-sg mode\n");
+		queue->use_sg = 0;
+		queue->queue.mem_ops = &vb2_vmalloc_memops;
+		goto retry;
+	}
 
 	return ret ? ret : rb->count;
 }