linux-kernel - Re: [PATCH v3] media: add virtio-media driver

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Message-Id: <DA6Q0LZPGS2D.2QCV889PQL2A7@gmail.com>
Date: Tue, 27 May 2025 15:14:50 +0900
From: "Alexandre Courbot" <gnurou@...il.com>
To: "Mauro Carvalho Chehab" <mchehab+huawei@...nel.org>, "Michael S.
 Tsirkin" <mst@...hat.com>
Cc: "Mauro Carvalho Chehab" <mchehab@...nel.org>, "Hans Verkuil"
 <hverkuil@...all.nl>, "Albert Esteve" <aesteve@...hat.com>, "Jason Wang"
 <jasowang@...hat.com>, "Xuan Zhuo" <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 <gurchetansingh@...gle.com>, <daniel.almeida@...labora.com>,
 <adelva@...gle.com>, <changyeon@...gle.com>,
 <nicolas.dufresne@...labora.com>, <linux-kernel@...r.kernel.org>,
 <linux-media@...r.kernel.org>, <virtualization@...ts.linux.dev>, "Alexandre
 Courbot" <acourbot@...gle.com>
Subject: Re: [PATCH v3] media: add virtio-media driver

Hi Mauro,

On Mon May 26, 2025 at 9:13 PM JST, Mauro Carvalho Chehab wrote:
> Hi Michael,
>
> Em Sat, 12 Apr 2025 13:08:01 +0900
> Alexandre Courbot <gnurou@...il.com> escreveu:
>
>> Add the first version of the virtio-media driver.
>>
>> This driver acts roughly as a V4L2 relay between user-space and the
>> virtio virtual device on the host, so it is relatively simple, yet
>> unconventional. It doesn't use VB2 or other frameworks typically used in
>> a V4L2 driver, and most of its complexity resides in correctly and
>> efficiently building the virtio descriptor chain to pass to the host,
>> avoiding copies whenever possible. This is done by
>> scatterlist_builder.[ch].
>>
>> virtio_media_ioctls.c proxies each supported ioctl to the host, using
>> code generated through macros for ioctls that can be forwarded directly,
>> which is most of them.
>>
>> virtio_media_driver.c provides the expected driver hooks, and support
>> for mmapping and polling.
>>
>>  This version supports MMAP buffers, while USERPTR buffers can also be
>>  enabled through a driver option. DMABUF support is still pending.
>
> It sounds that you applied this one at the virtio tree, but it hasn't
> being reviewed or acked by media maintainers.
>
> Please drop it.
>
> Alexandre,
>
> Please send media patches to media maintainers, c/c other subsystem
> maintainers, as otherwise they might end being merged without a
> proper review.

Sorry about that, I put everyone in "To:" without giving it a second
thought.

>
> In this particular case, we need to double-check if this won't cause
> any issues, in special with regards to media locks and mutexes.

Agreed, I am not 100% confident about that part myself.

>
> I'll try to look on it after this merge window, as it is too late
> for it to be applied during this one.

Appreciate that - given the high traffic on the list I was worried that
this patch would eventually be overlooked. Not making it for this merge
window should not be a problem, so please take the time you need.

Cheers,
Alex.