linux-kernel - Re: [PATCH v2] [media] of: move graph helpers from drivers/media/v4l2-core to drivers/media

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Date:	Wed, 12 Feb 2014 09:15:52 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Philipp Zabel <p.zabel@...gutronix.de>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>
CC:	Grant Likely <grant.likely@...aro.org>,
	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 v2] [media] of: move graph helpers from drivers/media/v4l2-core
 to drivers/media

Hi,

On 11/02/14 23:41, Philipp Zabel wrote:
> From: Philipp Zabel <philipp.zabel@...il.com>
> 
> This patch moves the parsing helpers used to parse connected graphs
> in the device tree, like the video interface bindings documented in
> Documentation/devicetree/bindings/media/video-interfaces.txt, from
> drivers/media/v4l2-core to drivers/media.
> 
> This allows to reuse the same parser code from outside the V4L2
> framework, most importantly from display drivers.
> The functions v4l2_of_get_next_endpoint, v4l2_of_get_remote_port,
> and v4l2_of_get_remote_port_parent are moved. They are renamed to
> of_graph_get_next_endpoint, of_graph_get_remote_port, and
> of_graph_get_remote_port_parent, respectively.
> Since there are not that many current users, switch all of them
> to the new functions right away.
> 
> Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> Acked-by: Mauro Carvalho Chehab <m.chehab@...sung.com>
> Acked-by: Guennadi Liakhovetski <g.liakhovetski@....de>

I don't think the graphs or the parsing code has anything video
specific. It could well be used for anything, whenever there's need to
describe connections between devices which are not handled by the normal
child-parent relationships. So the code could well reside in some
generic place, in my opinion.

Also, I have no problem with having it in drivers/media, but
drivers/video should work also. We already have other, generic, video
related things there like hdmi infoframes and display timings.

And last, it's fine to move the funcs as-is in the first place, but I
think they should be improved a bit before non-v4l2 users use them.
There are a couple of things I tried to accomplish with the omapdss
specific versions in
https://www.mail-archive.com/linux-omap@vger.kernel.org/msg100761.html:

- Iterating ports and endpoints separately. If a node has multiple
ports, I would think that the driver needs to know which port and
endpoint combination is the current one during iteration. It's not
enough to just get the endpoint.

- Simplify cases when there's just one port and one endpoint, in which
case the port node can be omitted from the DT data.

 Tomi



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