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From: Grant Likely <grant.likely@linaro.org>
Subject: Re: [RFC PATCH] [media]: of: move graph helpers from drivers/media/v4l2-core to drivers/of
To: Tomi Valkeinen <tomi.valkeinen@ti.com>,
        Philipp Zabel <p.zabel@pengutronix.de>
Cc: Sascha Hauer <s.hauer@pengutronix.de>, Rob Herring <robherring2@gmail.com>,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Mauro Carvalho Chehab <m.chehab@samsung.com>,
        Rob Herring <robh+dt@kernel.org>,
        Sylwester Nawrocki <s.nawrocki@samsung.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-media@vger.kernel.org" <linux-media@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Philipp Zabel <philipp.zabel@gmail.com>
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Date: Mon, 10 Mar 2014 14:41:02 +0000
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On Mon, 10 Mar 2014 12:18:20 +0200, Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
> On 08/03/14 13:41, Grant Likely wrote:
> 
> >> Ok. If we go for single directional link, the question is then: which
> >> way? And is the direction different for display and camera, which are
> >> kind of reflections of each other?
> > 
> > In general I would recommend choosing whichever device you would
> > sensibly think of as a master. In the camera case I would choose the
> > camera controller node instead of the camera itself, and in the display
> > case I would choose the display controller instead of the panel. The
> > binding author needs to choose what she things makes the most sense, but
> > drivers can still use if it it turns out to be 'backwards'
> 
> I would perhaps choose the same approach, but at the same time I think
> it's all but clear. The display controller doesn't control the panel any
> more than a DMA controller controls, say, the display controller.

In a sense it doesn't actually matter. You sensibly want to choose the
most likely direction that drivers would go looking for a device it
depends on, but it can be matched up at runtime regardless of the
direction chosen by the binding.

g.