Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935481AbdCLV3Q (ORCPT ); Sun, 12 Mar 2017 17:29:16 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:49859 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934858AbdCLV3L (ORCPT ); Sun, 12 Mar 2017 17:29:11 -0400 Date: Sun, 12 Mar 2017 22:29:04 +0100 From: Pavel Machek To: Russell King - ARM Linux Cc: Mauro Carvalho Chehab , Sakari Ailus , Hans Verkuil , Steve Longerbeam , robh+dt@kernel.org, mark.rutland@arm.com, shawnguo@kernel.org, kernel@pengutronix.de, fabio.estevam@nxp.com, mchehab@kernel.org, nick@shmanahar.org, markus.heiser@darmarIT.de, p.zabel@pengutronix.de, laurent.pinchart+renesas@ideasonboard.com, bparrot@ti.com, geert@linux-m68k.org, arnd@arndb.de, sudipm.mukherjee@gmail.com, minghsiu.tsai@mediatek.com, tiffany.lin@mediatek.com, jean-christophe.trotin@st.com, horms+renesas@verge.net.au, niklas.soderlund+renesas@ragnatech.se, robert.jarzmik@free.fr, songjun.wu@microchip.com, andrew-ct.chen@mediatek.com, gregkh@linuxfoundation.org, shuah@kernel.org, sakari.ailus@linux.intel.com, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, devel@driverdev.osuosl.org, Steve Longerbeam , Jacek Anaszewski Subject: Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline Message-ID: <20170312212904.GA7995@amd> References: <20170304131329.GV3220@valkosipuli.retiisi.org.uk> <20170310130733.GU21222@n2100.armlinux.org.uk> <20170310140124.GV21222@n2100.armlinux.org.uk> <20170310125342.7f047acf@vento.lan> <20170310223714.GI3220@valkosipuli.retiisi.org.uk> <20170311082549.576531d0@vento.lan> <20170311231456.GH21222@n2100.armlinux.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="7JfCtLOvnd9MIVvH" Content-Disposition: inline In-Reply-To: <20170311231456.GH21222@n2100.armlinux.org.uk> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3180 Lines: 81 --7JfCtLOvnd9MIVvH Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat 2017-03-11 23:14:56, Russell King - ARM Linux wrote: > On Sat, Mar 11, 2017 at 08:25:49AM -0300, Mauro Carvalho Chehab wrote: > > This situation is there since 2009. If I remember well, you tried to wr= ite > > such generic plugin in the past, but never finished it, apparently beca= use > > it is too complex. Others tried too over the years.=20 > >=20 > > The last trial was done by Jacek, trying to cover just the exynos4 driv= er.=20 > > Yet, even such limited scope plugin was not good enough, as it was never > > merged upstream. Currently, there's no such plugins upstream. > >=20 > > If we can't even merge a plugin that solves it for just *one* driver, > > I have no hope that we'll be able to do it for the generic case. >=20 > This is what really worries me right now about the current proposal for > iMX6. What's being proposed is to make the driver exclusively MC-based. >=20 > What that means is that existing applications are _not_ going to work > until we have some answer for libv4l2, and from what you've said above, > it seems that this has been attempted multiple times over the last _8_ > years, and each time it's failed. Yeah. We need a mid-layer between legacy applications and MC devices. Such layer does not exist in userspace or in kernel. > Loading the problem onto the user in the hope that the user knows > enough to properly configure it also doesn't work - who is going to > educate the user about the various quirks of the hardware they're > dealing with? We have docs. Users can write shell scripts. Still, mid-layer would be nice. > So, the problem space we have here is absolutely huge, and merely > having a plugin that activates when you open a /dev/video* node > really doesn't solve it. >=20 > All in all, I really don't think "lets hope someone writes a v4l2 > plugin to solve it" is ever going to be successful. I don't even > see that there will ever be a userspace application that is anything > more than a representation of the dot graphs that users can use to > manually configure the capture system with system knowledge. >=20 > I think everyone needs to take a step back and think long and hard > about this from the system usability perspective - I seriously > doubt that we will ever see any kind of solution to this if we > continue to progress with "we'll sort it in userspace some day." Mid-layer is difficult... there are _hundreds_ of possible pipeline setups. If it should live in kernel or in userspace is a question... but I don't think having it in kernel helps in any way. Best regards, Pavel --=20 (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blo= g.html --7JfCtLOvnd9MIVvH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iEYEARECAAYFAljFvaAACgkQMOfwapXb+vKR8gCcD5FQHJG8ZM1Y4tq2U1TLGrNL oO4AnRfJMH3U5KWa7FUscWzOUqeOqHuw =Ls/3 -----END PGP SIGNATURE----- --7JfCtLOvnd9MIVvH--