linux-kernel - Re: [RFC PATCH v2] media: Virtual camera driver

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Message-ID: <20260203212226.GF11369@killaraus>
Date: Tue, 3 Feb 2026 23:22:26 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: Jani Nikula <jani.nikula@...ux.intel.com>,
	johannes.goede@....qualcomm.com, linux-media@...r.kernel.org,
	anisse@...ier.eu, oleksandr@...alenko.name,
	linux-integrity@...r.kernel.org,
	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 v2] media: Virtual camera driver

On Tue, Feb 03, 2026 at 09:15:36PM +0200, Jarkko Sakkinen wrote:
> On Tue, Feb 03, 2026 at 09:07:41PM +0200, Jarkko Sakkinen wrote:
> > On Tue, Feb 03, 2026 at 08:53:13PM +0200, Jani Nikula wrote:
> > > On Tue, 03 Feb 2026, johannes.goede@....qualcomm.com wrote:
> > > > OTHO evdi: https://github.com/DisplayLink/evdi has been kept out
> > > > of the kernel for pretty much the same reasons by the drm/kms folks.
> > > >
> > > > At least AFAIK there still is no way to present virtual kms capable
> > > > display outputs backed by userspace in the kernel.
> > > >
> > > > I completely understand where you're coming from wrt v4l2-loopback
> > > > support (or something equivalent) but asking for this really is
> > > > the same as asking for the evdi driver to get merged, which AFAIK
> > > > has been blocked for the reason of avoiding proprietary userspace
> > > > display output drivers (I guess there might be technical reasons too).
> > > 
> > > I'm not sure this is the same thing, though.
> > > 
> > > The DRM subsystem does require an open source userspace for new uAPI,
> > > which is stricter than most subsystems [1]. Other than that, I don't
> > > think anyone's actively keeping evdi out of the kernel. AFAIK there
> > > hasn't been a serious attempt at upstreaming it either. Which is pretty
> > > much because there's no open userspace. Nobody's cared enough to either
> > > write one or open source the existing one for a decade [2].
> > 
> > This is unrelated of ACK/NACK and not saying this as a "selling point"
> > but realistically speaking based on what I've read I have extremely hard
> > time to believe that my driver would enable a market of proprietary
> > camera drivers :-) Actually, after looking up mipi.org based on Hans
> > response, I even more so believe that this is the case.
> 
> With my maintainer hat on, I'd get the nack better if the driver was
> intrusive on changes to V4L2 subsystem itself. Then, it accumlates
> weight to other maintainers, and as we all have limited amount of time
> in our lives, I do get that. But since the driver would be compliance
> aligning leaf driver with a MAINTAINER entry of its own, it should not
> be a huge burden for V4L2 community and kernel maintainers.  And I do
> have a track record of being long-term on maintaining stuff that I vomit
> out.

I don't dispute that. Even though we haven't really worked together on
kernel development, I have no prejudice towards your commitment as a
driver maintainer :-) There's nothing personal in this mail thread.

> That also does make difference as there are some guarantees that the
> end product would not be left into rotten.

-- 
Regards,

Laurent Pinchart