From: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: "Bryan O'Donoghue" <bryan.odonoghue@linaro.org>,
"Hans de Goede" <hdegoede@redhat.com>,
"Sumit Semwal" <sumit.semwal@linaro.org>,
"Benjamin Gaignard" <benjamin.gaignard@collabora.com>,
"Brian Starkey" <Brian.Starkey@arm.com>,
"John Stultz" <jstultz@google.com>,
"T.J. Mercier" <tjmercier@google.com>,
"Christian König" <christian.koenig@amd.com>,
"Lennart Poettering" <mzxreary@0pointer.de>,
"Robert Mader" <robert.mader@collabora.com>,
"Sebastien Bacher" <sebastien.bacher@canonical.com>,
"Linux Media Mailing List" <linux-media@vger.kernel.org>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
linaro-mm-sig@lists.linaro.org,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Milan Zamazal" <mzamazal@redhat.com>,
"Maxime Ripard" <mripard@redhat.com>,
"Andrey Konovalov" <andrey.konovalov.ynk@gmail.com>
Subject: Re: Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ?
Date: Tue, 7 May 2024 22:59:42 +0300 [thread overview]
Message-ID: <CAA8EJpqLu5w7gnqtDyuDDQBd7AEROTd6LTYi8muzjToXmkKR3w@mail.gmail.com> (raw)
In-Reply-To: <20240507184049.GC20390@pendragon.ideasonboard.com>
On Tue, 7 May 2024 at 21:40, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> On Tue, May 07, 2024 at 06:19:18PM +0300, Dmitry Baryshkov wrote:
> > On Tue, 7 May 2024 at 18:15, Bryan O'Donoghue wrote:
> > > On 07/05/2024 16:09, Dmitry Baryshkov wrote:
> > > > Ah, I see. Then why do you require the DMA-ble buffer at all? If you are
> > > > providing data to VPU or DRM, then you should be able to get the buffer
> > > > from the data-consuming device.
> > >
> > > Because we don't necessarily know what the consuming device is, if any.
> > >
> > > Could be VPU, could be Zoom/Hangouts via pipewire, could for argument
> > > sake be GPU or DSP.
> > >
> > > Also if we introduce a dependency on another device to allocate the
> > > output buffers - say always taking the output buffer from the GPU, then
> > > we've added another dependency which is more difficult to guarantee
> > > across different arches.
> >
> > Yes. And it should be expected. It's a consumer who knows the
> > restrictions on the buffer. As I wrote, Zoom/Hangouts should not
> > require a DMA buffer at all.
>
> Why not ? If you want to capture to a buffer that you then compose on
> the screen without copying data, dma-buf is the way to go. That's the
> Linux solution for buffer sharing.
Yes. But it should be allocated by the DRM driver. As Sima wrote,
there is no guarantee that the buffer allocated from dma-heaps is
accessible to the GPU.
>
> > Applications should be able to allocate
> > the buffer out of the generic memory.
>
> If applications really want to copy data and degrade performance, they
> are free to shoot themselves in the foot of course. Applications (or
> compositors) need to support copying as a fallback in the worst case,
> but all components should at least aim for the zero-copy case.
I'd say that they should aim for the optimal case. It might include
both zero-copying access from another DMA master or simple software
processing of some kind.
> > GPUs might also have different
> > requirements. Consider GPUs with VRAM. It might be beneficial to
> > allocate a buffer out of VRAM rather than generic DMA mem.
>
> Absolutely. For that we need a centralized device memory allocator in
> userspace. An effort was started by James Jones in 2016, see [1]. It has
> unfortunately stalled. If I didn't have a camera framework to develop, I
> would try to tackle that issue :-)
I'll review the talk. However the fact that the effort has stalled
most likely means that 'one fits them all' approach didn't really fly
well. We have too many usecases.
>
> [1] https://www.x.org/wiki/Events/XDC2016/Program/Unix_Device_Memory_Allocation.pdf
--
With best wishes
Dmitry
next prev parent reply other threads:[~2024-05-07 19:59 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-06 11:49 Safety of opening up /dev/dma_heap/* to physically present users (udev uaccess tag) ? Hans de Goede
2024-05-06 12:05 ` Maxime Ripard
2024-05-06 12:11 ` Hans de Goede
2024-05-06 13:38 ` Daniel Vetter
2024-05-06 14:01 ` Hans de Goede
2024-05-07 11:15 ` Daniel Vetter
2024-05-08 5:46 ` Daniel Stone
2024-05-08 8:33 ` Daniel Vetter
2024-05-08 8:38 ` Daniel Stone
2024-05-08 15:49 ` Daniel Vetter
2024-05-09 9:23 ` Daniel Stone
2024-05-16 10:18 ` Daniel Vetter
2024-05-13 13:51 ` Simon Ser
2024-05-16 10:13 ` Daniel Vetter
2024-05-16 11:49 ` Christian König
2024-05-07 13:34 ` Dmitry Baryshkov
2024-05-07 18:59 ` Laurent Pinchart
2024-05-22 13:34 ` Maxime Ripard
2024-05-23 9:41 ` Daniel Vetter
2024-05-07 13:32 ` Dmitry Baryshkov
2024-05-07 14:34 ` Hans de Goede
2024-05-07 15:09 ` Dmitry Baryshkov
2024-05-07 15:15 ` Bryan O'Donoghue
2024-05-07 15:19 ` Dmitry Baryshkov
2024-05-07 18:40 ` Laurent Pinchart
2024-05-07 19:59 ` Dmitry Baryshkov [this message]
2024-05-07 20:15 ` Laurent Pinchart
2024-05-08 8:39 ` Daniel Vetter
2024-05-08 21:54 ` Laurent Pinchart
2024-05-13 8:39 ` Maxime Ripard
2024-05-07 17:36 ` Daniel Vetter
2024-05-07 18:36 ` Laurent Pinchart
2024-05-07 20:07 ` Nicolas Dufresne
2024-05-08 8:36 ` Daniel Vetter
2024-05-08 21:51 ` Laurent Pinchart
2024-05-08 21:52 ` Laurent Pinchart
2024-05-13 8:29 ` Maxime Ripard
2024-05-13 8:34 ` Laurent Pinchart
2024-05-13 15:10 ` Nicolas Dufresne
2024-05-14 20:42 ` Laurent Pinchart
2024-05-15 17:43 ` nicolas.dufresne
2024-05-16 11:27 ` Laurent Pinchart
2024-05-16 17:11 ` nicolas.dufresne
2024-05-21 8:43 ` Maxime Ripard
2024-05-21 14:18 ` nicolas.dufresne
2024-05-16 7:00 ` Simon Ser
2024-05-16 11:20 ` Laurent Pinchart
2024-05-22 13:02 ` Nicolas Dufresne
2024-05-13 13:42 ` Nicolas Dufresne
2024-05-13 13:51 ` Maxime Ripard
2024-05-13 15:06 ` Nicolas Dufresne
2024-05-14 20:45 ` Laurent Pinchart
2024-05-14 20:52 ` Nicolas Dufresne
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