Hi,
This small patchset adds three new IOCTLs that can be used to attach, detach, or transfer from/to a DMABUF object.
This interface is being used at Analog Devices, to transfer data from high-speed transceivers to USB in a zero-copy fashion, using also the DMABUF import interface to the IIO subsystem which is being upstreamed in parallel [1] (and has high chances to be accepted for 5.9, I think Jonathan can confirm). The two are used by the Libiio software [2].
On a ZCU102 board with a FMComms3 daughter board, using the combination of these two new interfaces yields a drastic improvement of the throughput, from about 127 MiB/s using IIO's buffer read/write interface + read/write to the FunctionFS endpoints, to about 274 MiB/s when passing around DMABUFs, for a lower CPU usage (0.85 load avg. before, vs. 0.65 after).
Right now, *technically* there are no users of this interface, as Analog Devices wants to wait until both interfaces are accepted upstream to merge the DMABUF code in Libiio into the main branch, and Jonathan wants to wait and see if this patchset is accepted to greenlight the DMABUF interface in IIO as well. I think this isn't really a problem; once everybody is happy with its part of the cake, we can merge them all at once.
This is obviously for 5.9, and based on next-20240108.
Changelog:
- [3/4]: - Inline to_ffs_dma_fence() which was called only once. - Simplify ffs_dma_resv_lock() - Add comment explaining why we unref twice in ffs_dmabuf_detach() - Document uapi struct usb_ffs_dmabuf_transfer_req and IOCTLs - [4/4]: New patch, as I figured out having documentation wouldn't hurt.
Cheers, -Paul
[1] https://lore.kernel.org/linux-iio/219abc43b4fdd4a13b307ed2efaa0e6869e68e3f.c... [2] https://github.com/analogdevicesinc/libiio/tree/pcercuei/dev-new-dmabuf-api
Paul Cercueil (4): usb: gadget: Support already-mapped DMA SGs usb: gadget: functionfs: Factorize wait-for-endpoint code usb: gadget: functionfs: Add DMABUF import interface Documentation: usb: Document FunctionFS DMABUF API
Documentation/usb/functionfs.rst | 36 +++ drivers/usb/gadget/function/f_fs.c | 463 ++++++++++++++++++++++++++-- drivers/usb/gadget/udc/core.c | 7 +- include/linux/usb/gadget.h | 2 + include/uapi/linux/usb/functionfs.h | 41 +++ 5 files changed, 528 insertions(+), 21 deletions(-)