linux-kernel - Re: [PATCH 0/2] usb: gadget: functionfs: DMABUF import interface

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Message-ID: <777b760e-a9c2-cf46-c7be-26a4bcf633ab@amd.com>
Date:   Tue, 14 Mar 2023 13:01:50 +0100
From:   Christian König <christian.koenig@....com>
To:     Paul Cercueil <paul@...pouillou.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Cc:     michael.hennerich@...log.com, nuno.sa@...log.com,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH 0/2] usb: gadget: functionfs: DMABUF import interface

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(-)
>