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Date: Tue, 7 May 2024 16:34:24 +0200
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Subject: Re: Safety of opening up /dev/dma_heap/* to physically present users
 (udev uaccess tag) ?
To: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: 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>,
 =?UTF-8?Q?Christian_K=C3=B6nig?= <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>,
 Bryan O'Donoghue <bryan.odonoghue@linaro.org>,
 Milan Zamazal <mzamazal@redhat.com>, Maxime Ripard <mripard@redhat.com>,
 Andrey Konovalov <andrey.konovalov.ynk@gmail.com>
References: <bb372250-e8b8-4458-bc99-dd8365b06991@redhat.com>
 <ojduxo54lpcbfg2wfuhqhy7k3phncamtklh65z7gvttcwztmhk@zkifewcy4ovi>
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From: Hans de Goede <hdegoede@redhat.com>
In-Reply-To: <ojduxo54lpcbfg2wfuhqhy7k3phncamtklh65z7gvttcwztmhk@zkifewcy4ovi>
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Hi Dmitry,

On 5/7/24 3:32 PM, Dmitry Baryshkov wrote:
> On Mon, May 06, 2024 at 01:49:17PM +0200, Hans de Goede wrote:
>> Hi dma-buf maintainers, et.al.,
>>
>> Various people have been working on making complex/MIPI cameras work OOTB
>> with mainline Linux kernels and an opensource userspace stack.
>>
>> The generic solution adds a software ISP (for Debayering and 3A) to
>> libcamera. Libcamera's API guarantees that buffers handed to applications
>> using it are dma-bufs so that these can be passed to e.g. a video encoder.
>>
>> In order to meet this API guarantee the libcamera software ISP allocates
>> dma-bufs from userspace through one of the /dev/dma_heap/* heaps. For
>> the Fedora COPR repo for the PoC of this:
>> https://hansdegoede.dreamwidth.org/28153.html
> 
> Is there any reason for allocating DMA buffers for libcamera through
> /dev/dma_heap/ rather than allocating them via corresponding media
> device and then giving them away to DRM / VPU / etc?
> 
> At least this should solve the permission usecase: if the app can open
> camera device, it can allocate a buffer.

This is with a software ISP, the input buffers with raw bayer data
come from a v4l2 device, but the output buffers with the processed
data are purely userspace managed in this case.

Regards,

Hans