From: Xu Yang Date: Tue, 13 Jan 2026 09:53:10 +0000 (+0800) Subject: usb: gadget: uvc: retry vb2_reqbufs() with vb_vmalloc_memops if use_sg fail X-Git-Tag: v6.19-rc6~7^2~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9bcb4c4c330ca36ba7ab398c03d75c15b769d59d;p=thirdparty%2Flinux.git 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 Reviewed-by: Frank Li Link: https://patch.msgid.link/20260113-uvc-gadget-fix-patch-v2-4-62950ef5bcb5@nxp.com Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c index 21d80322cb61..586e5524c171 100644 --- a/drivers/usb/gadget/function/uvc_queue.c +++ b/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; }