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

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Date:	Tue, 11 Feb 2014 16:27:45 +0100
From:	Philipp Zabel <p.zabel@...gutronix.de>
To:	Rob Herring <robherring2@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Grant Likely <grant.likely@...aro.org>,
	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 Rob,

Am Dienstag, den 11.02.2014, 07:56 -0600 schrieb Rob Herring:
> 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...

I understand subsystem specific functionality is moving from drivers/of
into the subsystems. In this case three subsystems all could benefit
from the same set of parsing functions, so it is not clear to me where
if not drivers/of would be the correct place for this code.

> > 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.
>
> > I moved v4l2_of_get_next_endpoint, v4l2_of_get_remote_port,
> > and v4l2_of_get_remote_port_parent. They are renamed to
> > of_graph_get_next_endpoint, of_graph_get_remote_port, and
> > of_graph_get_remote_port_parent, respectively.
> >
> > Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
> > ---
> >  drivers/media/Kconfig             |   1 +
> >  drivers/media/v4l2-core/v4l2-of.c | 117 ---------------------------------
> >  drivers/of/Kconfig                |   3 +
> >  drivers/of/Makefile               |   1 +
> >  drivers/of/of_graph.c             | 133 ++++++++++++++++++++++++++++++++++++++
> >  include/linux/of_graph.h          |  23 +++++++
> >  include/media/v4l2-of.h           |  16 ++---
> >  7 files changed, 167 insertions(+), 127 deletions(-)
> >  create mode 100644 drivers/of/of_graph.c
> >  create mode 100644 include/linux/of_graph.h
> 
> [snip]
> 
> > diff --git a/include/media/v4l2-of.h b/include/media/v4l2-of.h
> > index 541cea4..404a493 100644
> > --- a/include/media/v4l2-of.h
> > +++ b/include/media/v4l2-of.h
> > @@ -17,6 +17,7 @@
> >  #include <linux/list.h>
> >  #include <linux/types.h>
> >  #include <linux/errno.h>
> > +#include <linux/of_graph.h>
> >
> >  #include <media/v4l2-mediabus.h>
> >
> > @@ -72,11 +73,6 @@ struct v4l2_of_endpoint {
> >  #ifdef CONFIG_OF
> >  int v4l2_of_parse_endpoint(const struct device_node *node,
> >                            struct v4l2_of_endpoint *endpoint);
> > -struct device_node *v4l2_of_get_next_endpoint(const struct device_node *parent,
> > -                                       struct device_node *previous);
> > -struct device_node *v4l2_of_get_remote_port_parent(
> > -                                       const struct device_node *node);
> > -struct device_node *v4l2_of_get_remote_port(const struct device_node *node);
> >  #else /* CONFIG_OF */
> >
> >  static inline int v4l2_of_parse_endpoint(const struct device_node *node,
> > @@ -85,25 +81,25 @@ static inline int v4l2_of_parse_endpoint(const struct device_node *node,
> >         return -ENOSYS;
> >  }
> >
> > +#endif /* CONFIG_OF */
> > +
> >  static inline struct device_node *v4l2_of_get_next_endpoint(
> >                                         const struct device_node *parent,
> >                                         struct device_node *previous)
> >  {
> > -       return NULL;
> > +       return of_graph_get_next_endpoint(parent, previous);
> 
> Won't this break for !OF?

It will. The of_graph_* functions should get their own stubs for that
case.

regards
Philipp

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