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Date:	Mon, 6 Oct 2014 15:58:18 +0200
From:	Boris Brezillon <boris.brezillon@...e-electrons.com>
To:	Thierry Reding <thierry.reding@...il.com>
Cc:	David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	Andrew Victor <linux@...im.org.za>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>, linux-pwm@...r.kernel.org,
	Rob Clark <robdclark@...il.com>,
	linux-arm-kernel@...ts.infradead.org,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, Mark Yao <mark.yao@...k-chips.com>
Subject: Re: [PATCH v7 10/11] ARM: at91/dt: add LCD panel description to
 sama5d3xdm.dtsi

On Mon, 6 Oct 2014 15:30:59 +0200
Thierry Reding <thierry.reding@...il.com> wrote:

> On Mon, Oct 06, 2014 at 03:11:11PM +0200, Boris Brezillon wrote:
> > On Mon, 6 Oct 2014 14:40:15 +0200
> > Thierry Reding <thierry.reding@...il.com> wrote:
> > 
> > > On Mon, Oct 06, 2014 at 02:25:38PM +0200, Boris Brezillon wrote:
> > > > On Mon, 6 Oct 2014 13:01:16 +0200 Thierry Reding <thierry.reding@...il.com> wrote:
> > > > > On Wed, Oct 01, 2014 at 04:53:07PM +0200, Boris Brezillon wrote:
> > > > > [...]
> > > > > > diff --git a/arch/arm/boot/dts/sama5d3xdm.dtsi b/arch/arm/boot/dts/sama5d3xdm.dtsi
> > > [...]
> > > > > > +		backlight = <&backlight>;
> > > > > > +		power-supply = <&panel_reg>;
> > > > > > +		#address-cells = <1>;
> > > > > > +		#size-cells = <0>;
> > > > > > +		status = "disabled";
> > > > > > +
> > > > > > +		port@0 {
> > > > > > +			#address-cells = <1>;
> > > > > > +			#size-cells = <0>;
> > > > > > +
> > > > > > +			panel_input: endpoint@0 {
> > > > > > +				reg = <0>;
> > > > > > +				remote-endpoint = <&hlcdc_panel_output>;
> > > > > > +			};
> > > > > >  		};
> > > > > 
> > > > > There's no support for OF graphs in simple-panel, so this is unused,
> > > > > isn't it?
> > > > 
> > > > Actually I use it in my atmel_hlcdc_ouput implementation to figure out
> > > > the link between a panel and a device connected on the RGB/DPI bus. 
> > > 
> > > That's kind of weird and one of the reasons why I can't make myself like
> > > the OF graph bindings. It requires drivers for one device to reach into
> > > the device tree node of some other device and look for content. Or put
> > > another way, a DT node for a panel that works on one platform doesn't
> > > work on another because the display controller needs additional DT
> > > content that isn't required by the original binding for the panel.
> > 
> > I also have a working POC of a DPI bus implementation (with DPI support
> > in panel-simple driver).
> > 
> > This is a solution I developed to provide a generic DPI implementation
> > in my HLCDC driver and rely on generic external implementations for
> > slave devices (panels, encoders, ...).
> > 
> > But, IIRC, Laurent was not in favor of a bus approach because the DPI
> > bus is just a data bus and not a control bus.
> > 
> > Anyway, I'll clean it up and post an RFC.
> 
> According to the MIPI website there are also control signals and a
> command set to control display behaviour. Does your implementation
> handle any of that?

No it doesn't, and I'm pretty sure what I call DPI does not exactly
respect the MIPI DPI standard (and as such should not be called DPI,
but this is another problem).

This infrastructure provides a way for devices connected on a DPI bus
to agree on a video_bus_format (in my case RGB888, RGB666, ...).

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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