Common bindings for video 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.

device {
	...
	ports {
		#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 remote 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, or port node needs to be associated with a selected hardware interface,
a common scheme using '#address-cells', '#size-cells' and 'reg' properties is
used.

All 'port' nodes can be grouped under optional 'ports' node, which allows to
specify #address-cells, #size-cells properties independently for the 'port'
and 'endpoint' nodes and any child device nodes a device might have.

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 other device.  In most
cases properties at the peer 'endpoint' nodes will be identical, however they
might need to be different when there is any signal modifications on the bus
between two devices, e.g. there are logic signal inverters on the lines.

It is allowed for multiple endpoints at a port to be active simultaneously,
where supported by a device.  For example, in case where a data interface of
a device is partitioned into multiple data busses, e.g. 16-bit input port
divided into two separate ITU-R BT.656 8-bit busses.  In such case bus-width
and data-shift properties can be used to assign physical data lines to each
endpoint node (logical bus).

Documenting bindings for devices
--------------------------------

All required and optional bindings the device supports shall be explicitly
documented in device DT binding documentation. This also includes port and
endpoint nodes for the device, including unit-addresses and reg properties where
relevant.

Please also see Documentation/devicetree/bindings/graph.txt .

Required properties
-------------------

If there is more than one 'port' or more than one 'endpoint' node or 'reg'
property is present in port and/or endpoint nodes the following properties
are required in a relevant parent node:

 - #address-cells : number of cells required to define port/endpoint
		    identifier, should be 1.
 - #size-cells    : should be zero.


Optional properties
-------------------

- flash-leds: An array of phandles, each referring to a flash LED, a sub-node
  of the LED driver device node.

- lens-focus: A phandle to the node of the focus lens controller.

- rotation: The camera rotation is expressed as the angular difference in
  degrees between two reference systems, one relative to the camera module, and
  one defined on the external world scene to be captured when projected on the
  image sensor pixel array.

  A camera sensor has a 2-dimensional reference system 'Rc' defined by
  its pixel array read-out order. The origin is set to the first pixel
  being read out, the X-axis points along the column read-out direction
  towards the last columns, and the Y-axis along the row read-out
  direction towards the last row.

  A typical example for a sensor with a 2592x1944 pixel array matrix
  observed from the front is:

              2591       X-axis          0
                <------------------------+ 0
                .......... ... ..........!
                .......... ... ..........! Y-axis
                           ...           !
                .......... ... ..........!
                .......... ... ..........! 1943
                                         V

  The external world scene reference system 'Rs' is a 2-dimensional
  reference system on the focal plane of the camera module. The origin is
  placed on the top-left corner of the visible scene, the X-axis points
  towards the right, and the Y-axis points towards the bottom of the
  scene. The top, bottom, left and right directions are intentionally not
  defined and depend on the environment in which the camera is used.

  A typical example of a (very common) picture of a shark swimming from
  left to right, as seen from the camera, is:

               0               X-axis
             0 +------------------------------------->
               !
               !
               !
               !           |\____)\___
               !           ) _____  __`<
               !           |/     )/
               !
               !
               !
               V
             Y-axis

  with the reference system 'Rs' placed on the camera focal plane:

                                  ¸.·˙!
                              ¸.·˙    !
                  _       ¸.·˙        !
               +-/ \-+¸.·˙            !
               | (o) |                ! Camera focal plane
               +-----+˙·.¸            !
                          ˙·.¸        !
                              ˙·.¸    !
                                  ˙·.¸!

  When projected on the sensor's pixel array, the image and the associated
  reference system 'Rs' are typically (but not always) inverted, due to
  the camera module's lens optical inversion effect.

  Assuming the above represented scene of the swimming shark, the lens
  inversion projects the scene and its reference system onto the sensor
  pixel array, seen from the front of the camera sensor, as follows:

            Y-axis
               ^
               !
               !
               !
               !            |\_____)\__
               !            ) ____  ___.<
               !            |/    )/
               !
               !
               !
             0 +------------------------------------->
               0               X-axis

  Note the shark being upside-down.

  The resulting projected reference system is named 'Rp'.

  The camera rotation property is then defined as the angular difference
  in the counter-clockwise direction between the camera reference system
  'Rc' and the projected scene reference system 'Rp'. It is expressed in
  degrees as a number in the range [0, 360[.

  Examples

  0 degrees camera rotation:


                    Y-Rp
                     ^
              Y-Rc   !
               ^     !
               !     !
               !     !
               !     !
               !     !
               !     !
               !     !
               !     !
               !   0 +------------------------------------->
               !     0               X-Rp
             0 +------------------------------------->
               0               X-Rc


                                X-Rc                0
               <------------------------------------+ 0
                           X-Rp                 0   !
           <------------------------------------+ 0 !
                                                !   !
                                                !   !
                                                !   !
                                                !   !
                                                !   !
                                                !   !
                                                !   !
                                                !   V
                                                !  Y-Rc
                                                V
                                               Y-Rp

  90 degrees camera rotation:

               0        Y-Rc
             0 +-------------------->
               !   Y-Rp
               !    ^
               !    !
               !    !
               !    !
               !    !
               !    !
               !    !
               !    !
               !    !
               !    !
               !  0 +------------------------------------->
               !    0              X-Rp
               !
               !
               !
               !
               V
              X-Rc

  180 degrees camera rotation:

                                            0
       <------------------------------------+ 0
                        X-Rc                !
              Y-Rp                          !
               ^                            !
               !                            !
               !                            !
               !                            !
               !                            !
               !                            !
               !                            !
               !                            V
               !                           Y-Rc
             0 +------------------------------------->
               0              X-Rp

  270 degrees camera rotation:

               0        Y-Rc
             0 +-------------------->
               !                                        0
               !    <-----------------------------------+ 0
               !                    X-Rp                !
               !                                        !
               !                                        !
               !                                        !
               !                                        !
               !                                        !
               !                                        !
               !                                        !
               !                                        !
               !                                        V
               !                                       Y-Rp
               !
               !
               !
               !
               V
              X-Rc


  Example one - Webcam

  A camera module installed on the user facing part of a laptop screen
  casing used for video calls. The captured images are meant to be
  displayed in landscape mode (width > height) on the laptop screen.

  The camera is typically mounted upside-down to compensate the lens
  optical inversion effect:

                    Y-Rp
              Y-Rc   ^
               ^     !
               !     !
               !     !       |\_____)\__
               !     !       ) ____  ___.<
               !     !       |/    )/
               !     !
               !     !
               !     !
               !   0 +------------------------------------->
               !     0           X-Rp
             0 +------------------------------------->
               0            X-Rc

  The two reference systems are aligned, the resulting camera rotation is
  0 degrees, no rotation correction needs to be applied to the resulting
  image once captured to memory buffers to correctly display it to users:

               +--------------------------------------+
               !                                      !
               !                                      !
               !                                      !
               !             |\____)\___              !
               !             ) _____  __`<            !
               !             |/     )/                !
               !                                      !
               !                                      !
               !                                      !
               +--------------------------------------+

  If the camera sensor is not mounted upside-down to compensate for the
  lens optical inversion, the two reference systems will not be aligned,
  with 'Rp' being rotated 180 degrees relatively to 'Rc':


                        X-Rc                0
       <------------------------------------+ 0
                                            !
              Y-Rp                          !
               ^                            !
               !                            !
               !       |\_____)\__          !
               !       ) ____  ___.<        !
               !       |/    )/             !
               !                            !
               !                            !
               !                            V
               !                           Y-Rc
             0 +------------------------------------->
               0            X-Rp

  The image once captured to memory will then be rotated by 180 degrees:

               +--------------------------------------+
               !                                      !
               !                                      !
               !                                      !
               !              __/(_____/|             !
               !            >.___  ____ (             !
               !                 \(    \|             !
               !                                      !
               !                                      !
               !                                      !
               +--------------------------------------+

  A software rotation correction of 180 degrees should be applied to
  correctly display the image:

               +--------------------------------------+
               !                                      !
               !                                      !
               !                                      !
               !             |\____)\___              !
               !             ) _____  __`<            !
               !             |/     )/                !
               !                                      !
               !                                      !
               !                                      !
               +--------------------------------------+

  Example two - Phone camera

  A camera installed on the back side of a mobile device facing away from
  the user. The captured images are meant to be displayed in portrait mode
  (height > width) to match the device screen orientation and the device
  usage orientation used when taking the picture.

  The camera sensor is typically mounted with its pixel array longer side
  aligned to the device longer side, upside-down mounted to compensate for
  the lens optical inversion effect:

               0        Y-Rc
             0 +-------------------->
               !   Y-Rp
               !    ^
               !    !
               !    !
               !    !
               !    !            |\_____)\__
               !    !            ) ____  ___.<
               !    !            |/    )/
               !    !
               !    !
               !    !
               !  0 +------------------------------------->
               !    0                X-Rp
               !
               !
               !
               !
               V
              X-Rc

  The two reference systems are not aligned and the 'Rp' reference
  system is rotated by 90 degrees in the counter-clockwise direction
  relatively to the 'Rc' reference system.

  The image once captured to memory will be rotated:

               +-------------------------------------+
               |                 _ _                 |
               |                \   /                |
               |                 | |                 |
               |                 | |                 |
               |                 |  >                |
               |                <  |                 |
               |                 | |                 |
               |                   .                 |
               |                  V                  |
               +-------------------------------------+

  A correction of 90 degrees in counter-clockwise direction has to be
  applied to correctly display the image in portrait mode on the device
  screen:

                        +--------------------+
                        |                    |
                        |                    |
                        |                    |
                        |                    |
                        |                    |
                        |                    |
                        |   |\____)\___      |
                        |   ) _____  __`<    |
                        |   |/     )/        |
                        |                    |
                        |                    |
                        |                    |
                        |                    |
                        |                    |
                        +--------------------+

- orientation: The orientation of a device (typically an image sensor or a flash
  LED) describing its mounting position relative to the usage orientation of the
  system where the device is installed on.
  Possible values are:
  0 - Front. The device is mounted on the front facing side of the system.
  For mobile devices such as smartphones, tablets and laptops the front side is
  the user facing side.
  1 - Back. The device is mounted on the back side of the system, which is
  defined as the opposite side of the front facing one.
  2 - External. The device is not attached directly to the system but is
  attached in a way that allows it to move freely.

Optional endpoint properties
----------------------------

- remote-endpoint: phandle to an 'endpoint' subnode of a remote device node.
- slave-mode: a boolean property indicating that the link is run in slave mode.
  The default when this property is not specified is master mode. In the slave
  mode horizontal and vertical synchronization signals are provided to the
  slave device (data source) by the master device (data sink). In the master
  mode the data source device is also the source of the synchronization signals.
- bus-type: data bus type. Possible values are:
  1 - MIPI CSI-2 C-PHY
  2 - MIPI CSI1
  3 - CCP2
  4 - MIPI CSI-2 D-PHY
  5 - Parallel
  6 - Bt.656
- bus-width: number of data lines actively used, valid for the parallel busses.
- data-shift: on the 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=<8>; data-shift=<2>;" means, that lines 9:2 are used.
- hsync-active: active state of the HSYNC signal, 0/1 for LOW/HIGH respectively.
- vsync-active: active state of the 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.
- data-enable-active: similar to HSYNC and VSYNC, specifies the data enable
  signal polarity.
- field-even-active: field signal level during the even field data transmission.
- pclk-sample: sample data on rising (1) or falling (0) edge of the pixel clock
  signal.
- sync-on-green-active: active state of Sync-on-green (SoG) signal, 0/1 for
  LOW/HIGH respectively.
- data-lanes: an array of physical data lane indexes. Position of an entry
  determines the 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.
  If the hardware does not support lane reordering, monotonically
  incremented values shall be used from 0 or 1 onwards, depending on
  whether or not there is also a clock lane. This property is valid for
  serial busses only (e.g. MIPI CSI-2).
- clock-lanes: an array of physical clock lane indexes. Position of an entry
  determines the logical lane number, while the value of an entry indicates
  physical lane, e.g. for a MIPI CSI-2 bus we could have "clock-lanes = <0>;",
  which places the clock lane on hardware lane 0. This property is valid for
  serial busses only (e.g. MIPI CSI-2). Note that for the MIPI CSI-2 bus this
  array contains only one entry.
- clock-noncontinuous: a boolean property to allow MIPI CSI-2 non-continuous
  clock mode.
- link-frequencies: Allowed data bus frequencies. For MIPI CSI-2, for
  instance, this is the actual frequency of the bus, not bits per clock per
  lane value. An array of 64-bit unsigned integers.
- lane-polarities: an array of polarities of the lanes starting from the clock
  lane and followed by the data lanes in the same order as in data-lanes.
  Valid values are 0 (normal) and 1 (inverted). The length of the array
  should be the combined length of data-lanes and clock-lanes properties.
  If the lane-polarities property is omitted, the value must be interpreted
  as 0 (normal). This property is valid for serial busses only.
- strobe: Whether the clock signal is used as clock (0) or strobe (1). Used
  with CCP2, for instance.

Example
-------

The example snippet below describes two data pipelines.  ov772x and imx074 are
camera sensors with a parallel and serial (MIPI CSI-2) video bus respectively.
Both sensors are on the I2C control bus corresponding to the i2c0 controller
node.  ov772x sensor is linked directly to the ceu0 video host interface.
imx074 is linked to ceu0 through the MIPI CSI-2 receiver (csi2). ceu0 has a
(single) DMA engine writing captured data to memory.  ceu0 node has a single
'port' node which may indicate that at any time only one of the following data
pipelines can be active: ov772x -> ceu0 or imx074 -> csi2 -> ceu0.

	ceu0: ceu@fe910000 {
		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>;

			/* Parallel bus endpoint */
			ceu0_1: endpoint@1 {
				reg = <1>;		/* Local endpoint # */
				remote = <&ov772x_1_1>;	/* Remote phandle */
				bus-width = <8>;	/* Used data lines */
				data-shift = <2>;	/* Lines 9:2 are used */

				/* If hsync-active/vsync-active are missing,
				   embedded BT.656 sync is used */
				hsync-active = <0>;	/* Active low */
				vsync-active = <0>;	/* Active low */
				data-active = <1>;	/* Active high */
				pclk-sample = <1>;	/* Rising */
			};

			/* MIPI CSI-2 bus endpoint */
			ceu0_0: endpoint@0 {
				reg = <0>;
				remote = <&csi2_2>;
			};
		};
	};

	i2c0: i2c@fff20000 {
		...
		ov772x_1: camera@21 {
			compatible = "ovti,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 for 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@1a {
			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@ffc90000 {
		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 {
				remote-endpoint = <&ceu0_0>;
			};
		};
	};