linux-kernel - Re: [PATCH v4 1/3] [media] of: move graph helpers from drivers/media/v4l2-core to drivers/of

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Message-Id: <20140320222631.2F0BBC412EA@trevor.secretlab.ca>
Date:	Thu, 20 Mar 2014 22:26:31 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Tomi Valkeinen <tomi.valkeinen@...com>,
	Philipp Zabel <p.zabel@...gutronix.de>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Rob Herring <robh+dt@...nel.org>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	devicetree@...r.kernel.org,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Philipp Zabel <philipp.zabel@...il.com>
Subject: Re: [PATCH v4 1/3] [media] of: move graph helpers from drivers/media/v4l2-core to drivers/of

On Mon, 10 Mar 2014 08:34:54 +0200, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
> On 08/03/14 14:23, Grant Likely wrote:
> 
> >>> That's fine. In that case the driver would specifically require the
> >>> endpoint to be that one node.... although the above looks a little weird
> >>
> >> The driver can't require that. It's up to the board designer to decide
> >> how many endpoints are used. A driver may say that it has a single input
> >> port. But the number of endpoints for that port is up to the use case.
> > 
> > Come now, when you're writing a driver you know if it will ever be
> > possible to have more than one port. If that is the case then the
> > binding should be specifically laid out for that. If there will never be
> > multiple ports and the binding is unambiguous, then, and only then,
> > should the shortcut be used, and only the shortcut should be accepted.
> 
> I was talking about endpoints, not ports. There's no unclarity about the
> number of ports, that comes directly from the hardware for that specific
> component. The number of endpoints, however, come from the board
> hardware. The driver writer cannot know that.

Okay, I understand now.

g.

> > Just to be clear, I have no problem with having the option in the
> > pattern, but the driver needs to be specific about what layout it
> > expects.
> 
> If we forget the shortened endpoint format, I think it can be quite
> specific.
> 
> A device has either one port, in which case it should require the
> 'ports' node to be omitted, or the device has more than one port, in
> which case it should require 'ports' node.
> 
> Note that the original v4l2 binding doc says that 'ports' is always
> optional.

The original v4l2 behaviour doesn't need to change. In fact it should
not change if it will cause real-world breakage.

g.
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