linux-kernel - Re: [GIT PULL] Move device tree graph parsing helpers to drivers/of

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Message-ID: <5327E74A.8030705@ti.com>
Date:	Tue, 18 Mar 2014 08:27:22 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Robert Schwebel <r.schwebel@...gutronix.de>,
	Grant Likely <grant.likely@...aro.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Rob Herring <robh+dt@...nel.org>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	<linux-kernel@...r.kernel.org>, <linux-media@...r.kernel.org>,
	<devicetree@...r.kernel.org>
Subject: Re: [GIT PULL] Move device tree graph parsing helpers to drivers/of

On 18/03/14 01:30, Laurent Pinchart wrote:

> I agree with you. I know that DT bindings review takes too much time, slows 
> development down and is just generally painful. I'm trying to reply to this e-
> mail thread as fast as possible, but I'm also busy with other tasks :-/
> 
> The lack of formal consensus comes partly from the fact that people are busy 
> and that the mail thread is growing big. There's still two open questions from 
> my view of the whole discussion:
> 
> - Do we really want to drop bidirectional links ? Grant has been pretty vocal 
> about that, but there has been several replies with arguments for 
> bidirectional links, and no reply from him afterwards. Even though that 
> wouldn't be the preferred solution for everybody, there doesn't seem to be a 
> strong disagreement about dropping bidirectional links, as long as we can come 
> up with a reasonable implementation.
> 
> - If we drop bidirectional links, what link direction do we use ? There has 
> been several proposals (including "north", which I think isn't future-proof as 
> it assumes an earth-centric model) and no real agreement, although there seems 
> to be a consensus among several developers that the core OF graph bindings 
> could leave that to be specified by subsystem bindings. We would still have to 
> agree on a direction for the display subsystem of course.
> 
> If my above explanation isn't too far from the reality the next step could be 
> to send a new version of the DT bindings proposal as a ping.

I agree with the above.

However, I also think we should just go forward with the bidirectional
links for now. The bindings for bidir links are already in the mainline
kernel, so they can't be seen as broken.

When we have an agreement about the direction, and we've got common
parsing code, it's trivial to convert the existing links to single
direction links, and the old dts files with bidir links continue to work
fine.

This is what I'm planning to do with OMAP display subsystem, as I
_really_ want to get the DT support merged for 3.15. The current mix of
pdata + DT that we have for OMAP display is an unmaintainable mess.

So unless I get a nack from someone (I've pinged Grant twice about
this), or someone explains why it's a bad idea, I'll push the OMAP
display bindings [1] for 3.15 with bidir bindings, and change them to
single-dir later.

Note that I did remove the abbreviated endpoint format that I had there
earlier, so now the bindings are fully compatible with the v4l2 bindings.

 Tomi

[1] http://article.gmane.org/gmane.linux.drivers.devicetree/63885



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