Re: [PATCH v7 10/11] ARM: at91/dt: add LCD panel description to sama5d3xdm.dtsi

From: Thierry Reding <thierry.reding@gmail.com>
To: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	linux-pwm@vger.kernel.org, devicetree@vger.kernel.org,
	Samuel Ortiz <sameo@linux.intel.com>,
	Pawel Moll <pawel.moll@arm.com>,
	Ian Campbell <ijc+devicetree@hellion.org.uk>,
	Lee Jones <lee.jones@linaro.org>,
	Nicolas Ferre <nicolas.ferre@atmel.com>,
	linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Rob Herring <robh+dt@kernel.org>,
	Alexandre Belloni <alexandre.belloni@free-electrons.com>,
	Kumar Gala <galak@codeaurora.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
	Andrew Victor <linux@maxim.org.za>,
	linux-arm-kernel@lists.infradead.org,
	Mark Yao <mark.yao@rock-chips.com>
Subject: Re: [PATCH v7 10/11] ARM: at91/dt: add LCD panel description to sama5d3xdm.dtsi
Date: Mon, 6 Oct 2014 15:30:59 +0200	[thread overview]
Message-ID: <20141006133048.GE26921@ulmo> (raw)
In-Reply-To: <20141006151111.446ed7d6@bbrezillon>

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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@gmail.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@gmail.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?

Thierry

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