Re: [PATCH] [media] Add common binding documentation for video interfaces

[Rob Herring <robherring2@gmail.com>]

On 12/15/2012 03:13 PM, Sylwester Nawrocki wrote:
> From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> 
> This patch adds a document describing common OF bindings for video
> capture, output and video processing devices. It is currently mainly
> focused on video capture devices, with data interfaces defined in
> standards like ITU-R BT.656 or MIPI CSI-2.
> It also documents a method of describing data links between devices.
> 
> Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
> Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>

Looks reasonable. You can merge this with the rest of the series.

Acked-by: Rob Herring <rob.herring@calxeda.com>

> ---
> Hi,
> 
> This is an updated version of patch [1]. My changes include resolving
> issues pointed out during review, i.e.:
>  - renaming 'link' node to 'endpoint,
>  - renaming 'remote' phandle to 'remote-endpoint',
>  - file v4l2.txt renamed to video-interfaces.txt,
>  - removed references to V4L2,
>  - added short description of the example DT snippet
> 
> and additionally:
>  - added "Required properties' paragraph,
>  - updated description of 'data-lanes' property,
>  - renamed all erroneous occurrences of 'data-width' to 'bus-width',
>  - added 'bus-width' property description,
>  - modified description of hsync-active, vsync-active properties,
>  - added a little paragraph further explaining that each endpoint
>    node has properties determining configuration of its corresponding
>    device.
> 
> [1] https://patchwork.kernel.org/patch/1514381/
> 
> I'm still unsure about the first sentence, as these bindings can be
> used for describing SoC internal connections between modules as well.
> 
> I was considering adding something like:
> 
> "This document describes common bindings for video capture, processing
> and output devices using data buses defined in standards like ITU-R
> BT.656, MIPI CSI-2,..."
> 
> before the "General concept" paragraph.
> 
> And maybe Documentation/devicetree/bindings/video/ would a better place
> for this video-interfaces.txt file ?
> 
> Thanks,
> Sylwester
> ---
>  .../devicetree/bindings/media/video-interfaces.txt |  198 ++++++++++++++++++++
>  1 files changed, 198 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/media/video-interfaces.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/video-interfaces.txt b/Documentation/devicetree/bindings/media/video-interfaces.txt
> new file mode 100644
> index 0000000..10ebbc4
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/video-interfaces.txt
> @@ -0,0 +1,198 @@
> +Common bindings for video data receiver and transmitter interfaces
> +
> +General concept
> +---------------
> +
> +Video data pipelines usually 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 their child 'port' nodes.
> +Configuration of a port depends on other devices participating in the data
> +transfer and is described by 'endpoint' subnodes.
> +
> +dev {
> +	#address-cells = <1>;
> +	#size-cells = <0>;
> +	port@0 {
> +		endpoint@0 { ... };
> +		endpoint@1 { ... };
> +	};
> +	port@1 { ... };
> +};
> +
> +If a port can be configured to work with more than one other device on the same
> +bus, an 'endpoint' child node must be provided for each of them.  If more than
> +one port is present in a device node or there is more than one endpoint at a
> +port, a common scheme, using '#address-cells', '#size-cells' and 'reg' properties
> +is used.
> +
> +Two 'endpoint' nodes are linked with each other through their 'remote-endpoint'
> +phandles.  An endpoint subnode of a device contains all properties needed for
> +configuration of this device for data exchange with the other device.  In most
> +cases properties at the peer 'endpoint' nodes will be identical, however
> +they might need to be different when there are any signal modifications on the
> +bus between two devices, e.g. there are logic signal inverters on the lines.
> +
> +Required properties
> +-------------------
> +
> +If there is more that one 'port' or more than one 'endpoint' node following
> +properties are required in relevant parent node:
> +
> +- #address-cells : number of cells required to define port number, should be 1.
> +- #size-cells    : should be zero.
> +
> +Optional endpoint properties
> +----------------------------
> +
> +- remote-endpoint : phandle to an 'endpoint' subnode of the other device node.
> +- slave-mode : a boolean property, run the link in slave mode. Default is master
> +  mode.
> +- bus-width : the number of data lines, valid for parallel buses.
> +- data-shift: on parallel data busses, if bus-width is used to specify the
> +  number of data lines, data-shift can be used to specify which data lines are
> +  used, e.g. "bus-width=<10>; data-shift=<2>;" means, that lines 9:2 are used.
> +- hsync-active : active state of HSYNC signal, 0/1 for LOW/HIGH respectively.
> +- vsync-active : active state of VSYNC signal, 0/1 for LOW/HIGH respectively.
> +  Note, that if HSYNC and VSYNC polarities are not specified, embedded
> +  synchronization 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 signal.
> +- data-lanes : an array of physical data lane indexes. Position of an entry
> +  determines logical lane number, while the value of an entry indicates physical
> +  lane, e.g. for 2-lane MIPI CSI-2 bus we could have "data-lanes = <1>, <2>;",
> +  assuming the clock lane is on hardware lane 0. This property is valid for
> +  serial buses only (e.g. MIPI CSI-2).
> +- clock-lanes : a number of physical lane used as a clock lane.
> +- clock-noncontinuous : a boolean property to allow MIPI CSI-2 non-continuous
> +  clock mode.
> +
> +Example
> +-------
> +
> +The below example snippet describes two data pipelines.  ov772x and imx074 are
> +camera sensors with parallel and serial (MIPI CSI-2) video bus respectively.
> +Both sensors are on I2C control bus corresponding to i2c0 controller node.
> +ov772x sensor is linked directly to the ceu0 video host interface.  imx074 is
> +linked to ceu0 through MIPI CSI-2 receiver (csi2). ceu0 has a (single) DMA
> +engine writing captured data to memory.  ceu0 node has single 'port' node which
> +indicates at any time only one of following data pipeline can be active:
> +ov772x -> ceu0 or imx074 -> csi2 -> ceu0.
> +
> +	ceu0: ceu@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: endpoint@1 {
> +				reg = <1>;		/* Local endpoint # */
> +				remote = <&ov772x_1_1>;	/* Remote phandle */
> +				bus-width = <8>;	/* Used data lines */
> +				data-shift = <0>;	/* Lines 7:0 are used */
> +
> +				/* If hsync-active/vsync-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: endpoint@0 {
> +				reg = <0>;
> +				remote = <&csi2_2>;
> +				immutable;
> +			};
> +		};
> +	};
> +
> +	i2c0: i2c@0xfff20000 {
> +		...
> +		ov772x_1: camera@0x21 {
> +			compatible = "omnivision,ov772x";
> +			reg = <0x21>;
> +			vddio-supply = <&regulator1>;
> +			vddcore-supply = <&regulator2>;
> +
> +			clock-frequency = <20000000>;
> +			clocks = <&mclk 0>;
> +			clock-names = "xclk";
> +
> +			port {
> +				/* With 1 endpoint per port no need in addresses. */
> +				ov772x_1_1: endpoint {
> +					bus-width = <8>;
> +					remote-endpoint = <&ceu0_1>;
> +					hsync-active = <1>;
> +					vsync-active = <0>; /* Who came up with an
> +							       inverter here ?... */
> +					data-active = <1>;
> +					pclk-sample = <1>;
> +				};
> +			};
> +		};
> +
> +		imx074: camera@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: endpoint {
> +					clock-lanes = <0>;
> +					data-lanes = <1>, <2>;
> +					remote-endpoint = <&csi2_1>;
> +				};
> +			};
> +		};
> +	};
> +
> +	csi2: csi2@0xffc90000 {
> +		compatible = "renesas,sh-mobile-csi2";
> +		reg = <0xffc90000 0x1000>;
> +		interrupts = <0x17a0>;
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@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: endpoint {
> +				clock-lanes = <0>;
> +				data-lanes = <2>, <1>;
> +				remote-endpoint = <&imx074_1>;
> +			};
> +		};
> +		port@2 {
> +			reg = <2>;			/* port 2: link to the CEU */
> +
> +			csi2_2: endpoint {
> +				immutable;
> +				remote-endpoint = <&ceu0_0>;
> +			};
> +		};
> +	};
> --
> 1.7.4.1
> 
> _______________________________________________
> devicetree-discuss mailing list
> devicetree-discuss@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/devicetree-discuss
>