From: Daniel Vetter <daniel.vetter@ffwll.ch>
To: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: "Jason Gunthorpe" <jgg@ziepe.ca>,
"DRI Development" <dri-devel@lists.freedesktop.org>,
LKML <linux-kernel@vger.kernel.org>,
"Daniel Vetter" <daniel.vetter@intel.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jérôme Glisse" <jglisse@redhat.com>, "Jan Kara" <jack@suse.cz>,
"Dan Williams" <dan.j.williams@intel.com>,
"Linux MM" <linux-mm@kvack.org>,
"Linux ARM" <linux-arm-kernel@lists.infradead.org>,
"Pawel Osciak" <pawel@osciak.com>,
"Kyungmin Park" <kyungmin.park@samsung.com>,
"Tomasz Figa" <tfiga@chromium.org>,
"Inki Dae" <inki.dae@samsung.com>,
"Joonyoung Shim" <jy0922.shim@samsung.com>,
"Seung-Woo Kim" <sw0312.kim@samsung.com>,
linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
"open list:DMA BUFFER SHARING FRAMEWORK"
<linux-media@vger.kernel.org>,
"Oded Gabbay" <oded.gabbay@gmail.com>
Subject: Re: [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM
Date: Wed, 7 Oct 2020 14:01:44 +0200 [thread overview]
Message-ID: <CAKMK7uF+a1PSn+e-6F+YhkSXn9vC7etS-z0AFBMCU+Vzb2PwqA@mail.gmail.com> (raw)
In-Reply-To: <d2f8e8a7-614d-18c8-9e2a-c604e5e54ce6@samsung.com>
On Wed, Oct 7, 2020 at 12:47 PM Marek Szyprowski
<m.szyprowski@samsung.com> wrote:
>
> Hi Daniel,
>
> On 03.10.2020 11:40, Daniel Vetter wrote:
> >> After he three places above should use pin_user_pages_fast(), then
> >> this whole broken API should be moved into videobuf2-memops.c and a
> >> big fat "THIS DOESN'T WORK" stuck on it.
> >>
> >> videobuf2 should probably use P2P DMA buf for this instead.
> > Yup this should be done with dma_buf instead, and v4l has that.
>
> Yes, V4L2 has dma_buf support NOW. That days, using so called V4L2
> USERPTR method was the only way to achieve zero copy buffer sharing
> between devices, so this is just a historical baggage. I've been
> actively involved in implementing that. I've tried to make it secure as
> much as possible assuming the limitation of that approach. With a few
> assumptions it works fine. Buffers are refcounted both by the
> vm_ops->open or by incrementing the refcount of the vm->file. This
> basically works with any sane driver, which doesn't free the mmaped
> buffer until the file is released. This is true for V4L2 and FBdev devices.
I'm not seeing any of that vm->file refcounting going on, so not
seeing anything that prevents the mmap area from being removed. Can
you pls give me some pointers about which code you're thinking of?
-Daniel
> This API is considered as deprecated in V4L2 world, so I think
> supporting this hack can be removed one day as nowadays userspace should
> use dma buf.
>
> > ...
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
next prev parent reply other threads:[~2020-10-07 12:02 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 17:53 [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Daniel Vetter
2020-10-02 17:53 ` [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Daniel Vetter
2020-10-02 18:06 ` Jason Gunthorpe
2020-10-02 18:16 ` Daniel Vetter
2020-10-02 23:31 ` Jason Gunthorpe
2020-10-03 8:34 ` Oded Gabbay
2020-10-03 9:40 ` Daniel Vetter
2020-10-04 12:50 ` Jason Gunthorpe
2020-10-04 16:09 ` Daniel Vetter
2020-10-05 17:28 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-05 18:37 ` Jason Gunthorpe
2020-10-05 18:54 ` Daniel Vetter
2020-10-05 22:43 ` Daniel Vetter
2020-10-05 23:41 ` Jason Gunthorpe
2020-10-06 6:23 ` Daniel Vetter
2020-10-06 12:26 ` Jason Gunthorpe
2020-10-06 13:08 ` Daniel Vetter
2020-10-07 10:47 ` Marek Szyprowski
2020-10-07 12:01 ` Daniel Vetter [this message]
2020-10-07 12:33 ` Marek Szyprowski
2020-10-07 12:44 ` Jason Gunthorpe
2020-10-07 12:47 ` Tomasz Figa
2020-10-07 12:58 ` Daniel Vetter
2020-10-07 13:06 ` Jason Gunthorpe
2020-10-07 13:34 ` Tomasz Figa
2020-10-07 13:42 ` Jason Gunthorpe
2020-10-07 14:08 ` Daniel Vetter
2020-10-07 14:11 ` Tomasz Figa
2020-10-07 14:22 ` Daniel Vetter
2020-10-07 15:05 ` Tomasz Figa
2020-10-07 14:58 ` Jason Gunthorpe
2020-10-07 13:06 ` Tomasz Figa
2020-10-07 13:14 ` Jason Gunthorpe
2020-10-05 15:03 ` Jan Kara
2020-10-02 22:39 ` John Hubbard
2020-10-03 9:45 ` Daniel Vetter
2020-10-03 22:52 ` John Hubbard
2020-10-03 23:24 ` Jason Gunthorpe
2020-10-04 11:20 ` Daniel Vetter
2020-10-05 17:35 ` Jason Gunthorpe
2020-10-02 18:22 ` [PATCH 1/2] mm/frame-vec: Drop gup_flags from get_vaddr_frames() Tomasz Figa
2020-10-02 19:21 ` Oded Gabbay
2020-10-05 17:38 [PATCH 2/2] mm/frame-vec: use FOLL_LONGTERM Jason Gunthorpe
2020-10-05 17:47 ` Jason Gunthorpe
2020-10-06 3:36 ` Andrew Morton
2020-10-06 11:57 ` Jason Gunthorpe
2020-10-05 17:53 ` Jan Kara
2020-10-05 17:57 ` Jason Gunthorpe
2020-10-05 18:16 ` Daniel Vetter
2020-10-06 11:56 ` Daniel Vetter
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