Hi,
This small patchset adds three new IOCTLs that can be used to attach, detach, or transfer from/to a DMABUF object.
This was surprisingly easy to add, as the functionfs code only uses scatterlists for transfers and allows specifying the number of bytes to transfer. The bulk of the code is then for general DMABUF accounting.
The patchset isn't tagged RFC but comments are very welcome, there are some things I am not 100% sure about: ffs_dma_resv_lock (with no ww_acquire_ctx), and I'm using pr_debug which feels wrong. Also, I should probably add documentation? The current IOCTLs for functionfs were not documented, as far as I can tell.
We use it with DMABUFs created with udmabuf, that we attach to the functionfs interface and to IIO devices (with a DMABUF interface for IIO, on its way to upstream too), to transfer samples from high-speed transceivers to USB in a zero-copy fashion.
Cheers, -Paul
Paul Cercueil (2): usb: gadget: Support already-mapped DMA SGs usb: gadget: functionfs: Add DMABUF import interface
drivers/usb/gadget/function/f_fs.c | 398 ++++++++++++++++++++++++++++ drivers/usb/gadget/udc/core.c | 7 +- include/linux/usb/gadget.h | 2 + include/uapi/linux/usb/functionfs.h | 14 +- 4 files changed, 419 insertions(+), 2 deletions(-)