[PATCH 04/14] media: add V4L2 DT binding documentation

[Guennadi Liakhovetski]

Hi Rob

On Tue, 2 Oct 2012, Rob Herring wrote:

> On 09/27/2012 09:07 AM, Guennadi Liakhovetski wrote:
> > This patch adds a document, describing common V4L2 device tree bindings.
> > 
> > Co-authored-by: Sylwester Nawrocki <s.nawrocki at samsung.com>
> > Signed-off-by: Guennadi Liakhovetski <g.liakhovetski at gmx.de>
> > ---
> >  Documentation/devicetree/bindings/media/v4l2.txt |  162 ++++++++++++++++++++++
> >  1 files changed, 162 insertions(+), 0 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/media/v4l2.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/media/v4l2.txt b/Documentation/devicetree/bindings/media/v4l2.txt
> > new file mode 100644
> > index 0000000..b8b3f41
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/media/v4l2.txt
> > @@ -0,0 +1,162 @@
> > +Video4Linux Version 2 (V4L2)
> 
> DT describes the h/w, but V4L2 is Linux specific. I think the binding
> looks pretty good in terms of it is describing the h/w and not V4L2
> components or settings. So in this case it's really just the name of the
> file and title I have issue with.

Hm, I see your point, then, I guess, you'd also like the file name 
changed. What should we use then? Just "video?" But there's already a 
whole directory Documentation/devicetree/bindings/video dedicated to 
graphics output (drm, fbdev). "video-camera" or "video-capture?" But this 
file shall also be describing video output. Use "video.txt" and describe 
inside what exactly this file is for?

> 
> One other comment below:
> 
> > +
> > +General concept
> > +---------------
> > +
> > +Video pipelines consist of external devices, e.g. camera sensors, controlled
> > +over an I2C, SPI or UART bus, and SoC internal IP blocks, including video DMA
> > +engines and video data processors.
> > +
> > +SoC internal blocks are described by DT nodes, placed similarly to other SoC
> > +blocks. External devices are represented as child nodes of their respective bus
> > +controller nodes, e.g. I2C.
> > +
> > +Data interfaces on all video devices are described by "port" child DT nodes.
> > +Configuration of a port depends on other devices participating in the data
> > +transfer and is described by "link" DT nodes, specified as children of the
> > +"port" nodes:
> > +
> > +/foo {
> > +	port at 0 {
> > +		link at 0 { ... };
> > +		link at 1 { ... };
> > +	};
> > +	port at 1 { ... };
> > +};
> > +
> > +If a port can be configured to work with more than one other device on the same
> > +bus, a "link" child DT node must be provided for each of them. If more than one
> > +port is present on a device or more than one link is connected to a port, a
> > +common scheme, using "#address-cells," "#size-cells" and "reg" properties is
> > +used.
> > +
> > +Optional link properties:
> > +- remote: phandle to the other endpoint link DT node.
> 
> This name is a little vague. Perhaps "endpoint" would be better.

"endpoint" can also refer to something local like in USB case. Maybe 
rather the description of the "remote" property should be improved?

Thanks
Guennadi

> 
> Rob
> 
> > +- slave-mode: a boolean property, run the link in slave mode. Default is master
> > +  mode.
> > +- data-shift: on parallel data busses, if data-width is used to specify the
> > +  number of data lines, data-shift can be used to specify which data lines are
> > +  used, e.g. "data-width=<10>; data-shift=<2>;" means, that lines 9:2 are used.
> > +- hsync-active: 1 or 0 for active-high or -low HSYNC signal polarity
> > +  respectively.
> > +- vsync-active: ditto for VSYNC. Note, that if HSYNC and VSYNC polarities are
> > +  not specified, embedded synchronisation may be required, where supported.
> > +- data-active: similar to HSYNC and VSYNC specifies data line polarity.
> > +- field-even-active: field signal level during the even field data transmission.
> > +- pclk-sample: rising (1) or falling (0) edge to sample the pixel clock pin.
> > +- data-lanes: array of serial, e.g. MIPI CSI-2, data hardware lane numbers in
> > +  the ascending order, beginning with logical lane 0.
> > +- clock-lanes: hardware lane number, used for the clock lane.
> > +- clock-noncontinuous: a boolean property to allow MIPI CSI-2 non-continuous
> > +  clock mode.
> > +
> > +Example:
> > +
> > +	ceu0: ceu at 0xfe910000 {
> > +		compatible = "renesas,sh-mobile-ceu";
> > +		reg = <0xfe910000 0xa0>;
> > +		interrupts = <0x880>;
> > +
> > +		mclk: master_clock {
> > +			compatible = "renesas,ceu-clock";
> > +			#clock-cells = <1>;
> > +			clock-frequency = <50000000>;	/* max clock frequency */
> > +			clock-output-names = "mclk";
> > +		};
> > +
> > +		port {
> > +			#address-cells = <1>;
> > +			#size-cells = <0>;
> > +
> > +			ceu0_1: link at 1 {
> > +				reg = <1>;		/* local link # */
> > +				remote = <&ov772x_1_1>;	/* remote phandle */
> > +				bus-width = <8>;	/* used data lines */
> > +				data-shift = <0>;	/* lines 7:0 are used */
> > +
> > +				/* If [hv]sync-active are missing, embedded bt.605 sync is used */
> > +				hsync-active = <1>;	/* active high */
> > +				vsync-active = <1>;	/* active high */
> > +				data-active = <1>;	/* active high */
> > +				pclk-sample = <1>;	/* rising */
> > +			};
> > +
> > +			ceu0_0: link at 0 {
> > +				reg = <0>;
> > +				remote = <&csi2_2>;
> > +				immutable;
> > +			};
> > +		};
> > +	};
> > +
> > +	i2c0: i2c at 0xfff20000 {
> > +		...
> > +		ov772x_1: camera at 0x21 {
> > +			compatible = "omnivision,ov772x";
> > +			reg = <0x21>;
> > +			vddio-supply = <&regulator1>;
> > +			vddcore-supply = <&regulator2>;
> > +
> > +			clock-frequency = <20000000>;
> > +			clocks = <&mclk 0>;
> > +			clock-names = "xclk";
> > +
> > +			port {
> > +				/* With 1 link per port no need in addresses */
> > +				ov772x_1_1: link {
> > +					bus-width = <8>;
> > +					remote = <&ceu0_1>;
> > +					hsync-active = <1>;
> > +					vsync-active = <0>;	/* who came up with an inverter here?... */
> > +					data-active = <1>;
> > +					pclk-sample = <1>;
> > +				};
> > +			};
> > +		};
> > +
> > +		imx074: camera at 0x1a {
> > +			compatible = "sony,imx074";
> > +			reg = <0x1a>;
> > +			vddio-supply = <&regulator1>;
> > +			vddcore-supply = <&regulator2>;
> > +
> > +			clock-frequency = <30000000>;	/* shared clock with ov772x_1 */
> > +			clocks = <&mclk 0>;
> > +			clock-names = "sysclk";		/* assuming this is the name in the datasheet */
> > +
> > +			port {
> > +				imx074_1: link {
> > +					clock-lanes = <0>;
> > +					data-lanes = <1>, <2>;
> > +					remote = <&csi2_1>;
> > +				};
> > +			};
> > +		};
> > +	};
> > +
> > +	csi2: csi2 at 0xffc90000 {
> > +		compatible = "renesas,sh-mobile-csi2";
> > +		reg = <0xffc90000 0x1000>;
> > +		interrupts = <0x17a0>;
> > +		#address-cells = <1>;
> > +		#size-cells = <0>;
> > +
> > +		port at 1 {
> > +			compatible = "renesas,csi2c";	/* one of CSI2I and CSI2C */
> > +			reg = <1>;			/* CSI-2 PHY #1 of 2: PHY_S, PHY_M has port address 0, is unused */
> > +
> > +			csi2_1: link {
> > +				clock-lanes = <0>;
> > +				data-lanes = <2>, <1>;
> > +				remote = <&imx074_1>;
> > +			};
> > +		};
> > +		port at 2 {
> > +			reg = <2>;			/* port 2: link to the CEU */
> > +
> > +			csi2_2: link {
> > +				immutable;
> > +				remote = <&ceu0_0>;
> > +			};
> > +		};
> > +	};
> > 
> 

---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/