linux-kernel - Re: [RFC PATCH] media: Virtual camera driver

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Message-ID: <20260201210144.GZ3374091@killaraus>
Date: Sun, 1 Feb 2026 23:01:44 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-media@...r.kernel.org, jani.nikula@...ux.intel.com,
	anisse@...ier.eu, oleksandr@...alenko.name,
	Mauro Carvalho Chehab <mchehab@...nel.org>,
	Hans Verkuil <hverkuil@...nel.org>,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Jacopo Mondi <jacopo.mondi@...asonboard.com>,
	Ricardo Ribalda <ribalda@...omium.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] media: Virtual camera driver

On Sun, Feb 01, 2026 at 10:35:06PM +0200, Jarkko Sakkinen wrote:
> On Sun, Feb 01, 2026 at 10:06:49PM +0200, Laurent Pinchart wrote:
> > On Sun, Feb 01, 2026 at 09:04:00PM +0200, Jarkko Sakkinen wrote:
> > > On Sun, Feb 01, 2026 at 08:20:11PM +0200, Laurent Pinchart wrote:
> > > > On Sun, Feb 01, 2026 at 03:33:38PM +0200, Jarkko Sakkinen wrote:
> > > > > vcam is a DMA-BUF backed virtual camera driver capable of creating video
> > > > > capture devices to which data can be streamed through /dev/vcam after
> > > > > calling VCAM_IOC_CREATE. Frames are pushed with VCAM_IOC_QUEUE and recycled
> > > > > with VCAM_IOC_DEQUEUE.
> > > > > 
> > > > > Zero-copy semantics are supported for shared DMA-BUF between capture and
> > > > > output.
> > > > >
> > > > > Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> > > > > ---
> > > > > Early feedback e.g., is this completely in wrong direction? V4L2 world
> > > > > is relatively alien world, and thus I need a sanity check ;-)
> > > > 
> > > > We already have multiple virtual drivers, including vivid and vimc.
> > > > Could you please explain the rationale for yet another one, and why the
> > > > new features it provides (if any) can't be added to existing drivers ?
> > > 
> > > There is a notable user base for v4l2-loopback. It is the defacto choice
> > > for streaming phone cams.
> > 
> > This will then likely face the same hurdles as v4l2-loopback, the main
> > one being that camera support should be upstreamed with proper drivers
> > instead of a closed-source userspace daemon.
> > 
> > For phone cameras, the way forward upstream is libcamera. Until kernel
> > drivers for ISPs are available, the soft ISP is a stop-gap solution. It
> > recently gained GPU acceleration support (with work to improve image
> > quality with additional algorithms ongoing).
> 
> That might have some weight as a pro but the unarguable con is that at
> the same time this policy retains a base of tainted kernels in the wild.

Do you mean tainted by the out-of-tree v4l2loopback module ? Won't those
systems be equally tainted by out-of-tree camera drivers then ? With
libcamera and the soft ISP you can run a 100% mainline stack.

> Not saying that this weight more but it is important to remark this
> fact.
> 
> > > The motivation here is to provide a service optimized for that use and
> > > purpose. It's virtual but non-generic i.e. not aimed for testing/emulation.
> > > 
> > > > >  .../driver-api/media/drivers/index.rst        |    1 +
> > > > >  .../driver-api/media/drivers/vcam.rst         |   16 +
> > > > >  MAINTAINERS                                   |    8 +
> > > > >  drivers/media/Kconfig                         |   13 +
> > > > >  drivers/media/Makefile                        |    1 +
> > > > >  drivers/media/vcam.c                          | 1700 +++++++++++++++++
> > > > >  include/uapi/linux/vcam.h                     |  124 ++
> > > > >  7 files changed, 1863 insertions(+)
> > > > >  create mode 100644 Documentation/driver-api/media/drivers/vcam.rst
> > > > >  create mode 100644 drivers/media/vcam.c
> > > > >  create mode 100644 include/uapi/linux/vcam.h
> > 
> > [snip]

-- 
Regards,

Laurent Pinchart