[0/2] usb: gadget: functionfs: DMABUF import interface

Message

Paul Cercueil March 14, 2023, 10:52 a.m. UTC

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(-)

Comments

Christian König March 14, 2023, 12:01 p.m. UTC | #1

Am 14.03.23 um 11:52 schrieb Paul Cercueil:
> 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),

That is perfectly fine as long as you only want to lock one dma_resv object.

I've made a few notes what should be fixed and could potentially be 
improved, but from the DMA-buf side that looks like it should mostly work.

Regards,
Christian.

>   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(-)
>