linux-kernel - Re: [PATCH v2 0/3] DCMI bridge support

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Message-ID: <20190705091637.b5626yvkycumsp6z@paasikivi.fi.intel.com>
Date:   Fri, 5 Jul 2019 12:16:37 +0300
From:   Sakari Ailus <sakari.ailus@...ux.intel.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Hugues FRUCHET <hugues.fruchet@...com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-stm32@...md-mailman.stormreply.com" 
        <linux-stm32@...md-mailman.stormreply.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Philippe CORNU <philippe.cornu@...com>,
        Mickael GUENE <mickael.guene@...com>
Subject: Re: [PATCH v2 0/3] DCMI bridge support

Hi Laurent,

On Fri, Jul 05, 2019 at 11:04:24AM +0300, Laurent Pinchart wrote:

...

> > A reasonable compromise would be to add a Kconfig option that allows
> > enabling MC. This way you can provide backwards compatibility and allow
> > making use of the full potential of the hardware. That's also why hardware
> > that may be part of a non-trivial MC pipeline should start with MC-enabled
> > so we wouldn't run into this.
> 
> I really don't like this, as it introduces additional complexity. My
> recommendation is to go for an MC-centric approach. Going for a video
> node-centric approach is really shooting oneself in the foot regarding
> future extensions. But that being said, if there's a strong desire to go
> for foot self-shooting, the way to go is explained above.

Well, there's nothing that can be done anymore as this has already
happened: this is an existing driver in the mainline kernel. Unless you
have a time machine of some sort, of course. :-) The choice is now really
between breaking existing applications (plain V4L2) and supporting new
functionality (MC-centric), so if you need both, I don't really see another
choice than a Kconfig option.

On the other hand, if we know there are no existing users that could not
support the MC-centric view of the device, we could just change the driver
API and forget the Kconfig option. It'd be much more simple that way
indeed. But I don'k know what's the case.

-- 
Regards,

Sakari Ailus
sakari.ailus@...ux.intel.com