Hi Sylwester

Ok, looks like there are no more comments coming, so, we can submit a new 
version:-)

Thanks for your comments:

On Tue, 11 Sep 2012, Sylwester Nawrocki wrote:

Hi Guennadi,

On 09/11/2012 05:51 PM, Guennadi Liakhovetski wrote:

quoted

This patch adds a document, describing common V4L2 device tree bindings.

Co-authored-by: Sylwester Nawrocki [off-list ref]
Signed-off-by: Guennadi Liakhovetski <redacted>
---
 Documentation/devicetree/bindings/media/v4l2.txt |  143 ++++++++++++++++++++++
 1 files changed, 143 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..55da6de
--- /dev/null
+++ b/Documentation/devicetree/bindings/media/v4l2.txt

@@ -0,0 +1,143 @@
+Video4Linux Version 2 (V4L2)
+
+General concept:
+- video pipelines consist of external devices, e.g., camera sensors, controlled
+  over an I2C bus, and SoC internal IP blocks, including video DMA engines and
+  video data processors.
+- this document describes common bindings of all video pipeline devices.
+- SoC internal blocks are described by DT nodes, placed similarly to other SoC
+  blocks.
+- external devices are places on their respective control busses, e.g., I2C
+- data interfaces on all video devices are described by "port" child DT nodes
+- port configuration depends on other devices, participating in the data
+  transfer, and is described by "link" DT nodes, specified as children of
+  all "port" nodes, connected to this bus.
+- 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.

How about rephrasing/rearranging this to:

This document describes common bindings of all video pipeline devices.

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.

Well, I don't mind. I looked at a random file under 
Documentation/devicetree/bindings and used the same style, but we can use 
a free-flowing text too.

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@0 {
		link@0 { ... };
		link@1 { ... };
	};
	port@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.

quoted

+Optional link properties:
+- remote: phandle to the other endpoint link DT node.
+- data-shift: on parallel data busses, if data-width is used to specify the

s/busses/buses

Nnnnooo... I think, "busses" is British and "buses" is American English, 
and I'm usually trying to follow the former, as much as I can:-) Also see 
"drivers/i2c/busses/"

quoted

+  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.
+- pclk-sample: rising (1) or falling (0) edge to sample the pixel clock pin.
+- immutable: used for SoC-internal links, if no configuration is required.
+- data-lanes: array of serial, e.g., MIPI CSI-2, data hardware lane numbers in

nit: s/e.g.,/e.g. ?

This is a good question, actually. Until now I've been following a 
suggestion by some well-educated British friend of mine, who told me to 
use commas on either side of "e.g." and "i.e." But in most textx I read I 
indeed see only one comma - before those. So, I tried to search and got a 
couple of hits, which suggest, that putting a comma on both sides or at 
least _after_ those abbreviations is more American grammar, and only 
before is more British... So, I think I'll follow your advise on this too 
and switch to the no-comma-after style, thanks.

quoted

+  the ascending order, beginning with logical lane 0.
+- clock-lanes: hardware lane number, used for the clock lane.

s/clock lane/clock ?

Well, to me both make sense. The meanings are a bit different, but none 
seems wrong to me. My version seems a bit more specific - not just "some" 
clock, but the CSI-2 clock lane?

quoted

+
+Example:
+
+	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: link@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 */
+				pclk-sample = <1>;	/* rising */
+			};
+
+			ceu0_0: link@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 link per port no need in addresses */

s/in/for ?

Ehm, no idea either. Both "no need in" and "no need for" produce enough 
hits in search engines:-)

quoted

+				ov772x_1_1: link {
+					bus-width = <8>;
+					remote = <&ceu0_1>;
+					hsync-active = <1>;
+					hsync-active = <0>;	/* who came up with an inverter here?... */
+					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: link {
+					clock-lanes = <0>;
+					data-lanes = <1>, <2>;
+					remote = <&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: link {
+				clock-lanes = <0>;
+				data-lanes = <2>, <1>;
+				remote = <&imx074_1>;
+			};
+		};
+		port@2 {
+			reg = <2>;			/* port 2: link to the CEU */
+
+			csi2_2: link {
+				immutable;
+				remote = <&ceu0_0>;
+			};
+		};
+	};

--

Regards,
Sylwester

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