anyone knows which kernel version supports dma_buf for v4l2src?

[Nicolas Dufresne]

To answer that question, you have to read the appropriate kernel driver.
What I think is the state of UVC, because it's using the vmalloc
allocator, is that it is most likely able to important (queue) dmabuf
but not export dmabuf. But I have not verified that, asking a real V4L2
expert would probably be better (freenote #v4l). On most platform,
buffers allocated from vmalloc cannot be used for DMA operation. IOMMU
should relax this limitation eventually, on capable hardware.

The state of GStreamer is that we only support exporting DMABUF at the
moment. Importing DMABUF is very similar to supporting USERPTR, without
the limitation of having to guess what allocator the driver is using.
Note that I am working on a project that should, in the first place,
enable USERPTR to work for certain (selected) drivers. This should lead
the way into implementing DMABUF importation, which should not require
drivers white listing.

cheers,
Nicolas
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