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

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Date:	Tue, 18 Feb 2014 14:41:43 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Grant Likely <grant.likely@...aro.org>
Cc:	Rob Herring <robherring2@...il.com>,
	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>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Philipp Zabel <philipp.zabel@...il.com>
Subject: Re: [RFC PATCH] [media]: of: move graph helpers from
 drivers/media/v4l2-core to drivers/of

Hi Grant,

Am Montag, den 17.02.2014, 18:14 +0000 schrieb Grant Likely:
> On Tue, 11 Feb 2014 07:56:33 -0600, Rob Herring <robherring2@...il.com> wrote:
> > On Tue, Feb 11, 2014 at 5:45 AM, Philipp Zabel <p.zabel@...gutronix.de> 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/of.
> > 
> > This is the opposite direction things have been moving...
> > 
> > > This allows to reuse the same parser code from outside the V4L2 framework,
> > > most importantly from display drivers. There have been patches that duplicate
> > > the code (and I am going to send one of my own), such as
> > > http://lists.freedesktop.org/archives/dri-devel/2013-August/043308.html
> > > and others that parse the same binding in a different way:
> > > https://www.mail-archive.com/linux-omap@vger.kernel.org/msg100761.html
> > >
> > > I think that all common video interface parsing helpers should be moved to a
> > > single place, outside of the specific subsystems, so that it can be reused
> > > by all drivers.
> > 
> > Perhaps that should be done rather than moving to drivers/of now and
> > then again to somewhere else.
> 
> This is just parsing helpers though, isn't it? I have no problem pulling
> helper functions into drivers/of if they are usable by multiple
> subsystems. I don't really understand the model being used though. I
> would appreciate a description of the usage model for these functions
> for poor folks like me who can't keep track of what is going on in
> subsystems.

I have taken the liberty to put you on Cc: for the i.MX drm series that
I'd like to use these helpers in. The patch in question is
"[RFC PATCH v3 3/9] staging: imx-drm-core: Use OF graph to find
components and connections between encoder and crtcs"
(http://www.spinics.net/lists/arm-kernel/msg308542.html).
It currently uses local copies (s/of_graph/imx_drm_of/) of the
get_next_endpoint, get_remote_port, and get_remote_port_parent
functions to obtain all necessary components for the componentized
imx-drm device, and to map the connections between crtcs (display
interface ports) and encoders.

regards
Philipp

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