Message-Id: <200812011524.43499.laurent.pinchart@skynet.be>
Date:	Mon, 1 Dec 2008 15:24:43 +0100
From:	Laurent Pinchart <laurent.pinchart@...net.be>
To:	Hans Verkuil <hverkuil@...all.nl>
Cc:	video4linux-list@...hat.com,
	"v4l-dvb maintainer list" <v4l-dvb-maintainer@...uxtv.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	davinci-linux-open-source-bounces@...ux.davincidsp.com,
	Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [PULL] http://www.linuxtv.org/hg/~hverkuil/v4l-dvb-ng

Hi Hans,

On Monday 01 December 2008, Hans Verkuil wrote:
> On Monday 01 December 2008 14:29:53 Laurent Pinchart wrote:
> > On Monday 01 December 2008, Hans Verkuil wrote:
> > > On Monday 01 December 2008 13:31:25 Laurent Pinchart wrote:
> > > > On Monday 01 December 2008, Hans Verkuil wrote:
> > > > > Hi Mauro,
> > > > >
> > > > > Please pull from http://www.linuxtv.org/hg/~hverkuil/v4l-dvb-ng
> > > > > for the following:
> > > > >
> > > > > - v4l2: add v4l2_device and v4l2_subdev structs to the v4l2
> > > > > framework. - v4l2-common: add i2c helper functions
> > > > > - cs53l32a: convert to v4l2_subdev.
> > > > > - cx25840: convert to v4l2_subdev.
> > > > > - m52790: convert to v4l2_subdev.
> > > > > - msp3400: convert to v4l2_subdev.
> > > > > - saa7115: convert to v4l2_subdev.
> > > > > - saa7127: convert to v4l2_subdev.
> > > > > - saa717x: convert to v4l2_subdev.
> > > > > - tuner: convert to v4l2_subdev.
> > > > > - upd64031a: convert to v4l2_subdev.
> > > > > - upd64083: convert to v4l2_subdev.
> > > > > - vp27smpx: convert to v4l2_subdev.
> > > > > - wm8739: convert to v4l2_subdev.
> > > > > - wm8775: convert to v4l2_subdev.
> > > > > - ivtv/ivtvfb: convert to v4l2_device/v4l2_subdev.
> > > > >
> > > > > All points raised in reviews are addressed so I think it is
> > > > > time to get this merged so people can start to use it.
> > > >
> > > > Does linuxtv.org and Mercurial provide the necessary
> > > > infrastructure to integrate those changes into the v4l-dvb
> > > > repository while not pushing them upstream yet ? I'd like to see
> > > > more people testing (and breaking and fixing :-)) your changes
> > > > before they reach the mainline kernel.
> > >
> > > That's basically why I want this to go into the v4l-dvb repository:
> > > this makes it easier for people to start working with it. It
> > > doesn't affect existing drivers, except for the i2c driver changes
> > > and those changes are just transforming a big switch to a set of
> > > functions. So I really consider this a pretty low-risk merge.
> > >
> > > If someone is willing to do some testing with my tree in the next
> > > two weeks then I don't mind waiting, but it's been in development
> > > now from early September (if not earlier) and been reviewed several
> > > times. In addition, ivtv has been modified to work with it and that
> > > driver uses more sub-devices by far than any other driver.
> > >
> > > I don't know what more I can do, to be honest.
> >
> > I am all for pushing the changes to the v4l-dvb repository so they
> > can get broader testing. I am, however, a bit more concerned about
> > pushing the changes to Linus yet.
>
> They will of course go to linux-next and end up in 2.6.29 when the merge
> window opens. It's obviously not for 2.6.28.

I would say 2.6.29 is a bit early, but I can live with that.

> > Shouldn't it wait until you convert
> > other drivers and make the v4l2_device (infra)structure more
> > powerful, as you announced you would ? There will probably be API/ABI
> > breakage then, it patches will probably benefit from a few iterations
> > in v4l-dvb before we push them to mainline.
>
> Yes, I want to add more features to them, but those additions need a lot
> more thought. Currently the new subdev support is the most important
> feature of this and the reason is the introduction of v4l2-int-device
> and soc-camera: both are recent arrivals and neither was reviewed
> properly. As a result we now see i2c drivers arriving that can only
> work with v4l2-int-device or with soc-camera infrastructure. This is
> very undesirable and must be fixed asap.

Agreed.

> And v4l2_subdev is the way to do this. Existing i2c drivers are not affected
> and when these changes are in we can start to replace v4l2-int-device.h and
> to modify soc-camera to use v4l2_subdev as well.

Ok.

> In addition, these changes make it easier as well to use the new i2c API
> in bridge drivers (in 2.6.29 the old-style I2C probing will be
> deprecated, so we need to convert). So we get many benefits with just
> these changes.
> Of course, I want to add more v4l2 framework support to these new
> structures, but I don't have any code yet for that anyway, just lots of
> ideas. Start simple, then expand.
>
> > I don't know if that's possible at all, or if all changes in v4l-dvb
> > are automatically selected for a push to the git repository whenever
> > Mauro triggers the hg->git process.
>
> Well, they go to linux-next, but is that a problem?

In a few months time (probably even earlier) the v4l2_device structure will be 
reworked (and possible renamed). I'm fine with it going to linux-next now if 
we agree on the following.

- We should only advocate v4l2_device usage for subdevices-aware video 
devices. Porting all drivers to v4l2_device is currently pointless and will 
only make future transitions more difficult.

- v4l2_device should be marked as experimental. I don't want to hear any 
API/ABI breakage argument in a few months time when the framework will 
evolve.

Best regards,

Laurent Pinchart
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