RE: [EXT] Re: [PATCH] media: videobuf2-dma-sg: limit the sg segment size

Hui Fang
2023-09-04T07:10:16Z

On Wed, Aug 30, 2023 at 6:20 PM Tomasz Figa <tfiga@chromium.org> wrote:
> On Wed, Aug 30, 2023 at 5:50 PM Hui Fang <hui.fang@nxp.com> wrote:
......
> > I wonder if only NXP met the "swiotlb buffer full" issue. In theory,
> > when format is YUYV, those resolutions no greater than 320x240 (153600
> > bytes, which less than the max mapping size 256K ) can't meet the issue.
> > But resolutions no less than 640x480 (307200 bytes), may have chances
> > to trigger the issue.
>
> I think a combination of a device that can support scatter-gather, but requires
> swiotlb is kind of rare. Most drivers would require a single contiguous DMA
> address (and thus use videobuf2-dma-contig) and physical discontinuity would
> be handled by an IOMMU (transparently to vb2).
>
> I guess one thing to ask you about your specific setup is whether it's expected
> that the swiotlb ends up being used at all?

Yes, the swiotlb ends up being used. We met the issue when bring up
DeviceAsWebCam (android-14 new feature, android device works as a usb camera).

BRs,
Fang Hui