[media] dt-bindings: media: Add Renesas R-Car DRIF binding

Add binding documentation for Renesas R-Car Digital Radio Interface
(DRIF) controller.
Signed-off-by: Ramesh Shanmugasundaram <ramesh.shanmugasundaram@bp.renesas.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/devicetree/bindings/media/renesas,drif.txt

+Renesas R-Car Gen3 Digital Radio Interface controller (DRIF)
+------------------------------------------------------------
+
+R-Car Gen3 DRIF is a SPI like receive only slave device. A general
+representation of DRIF interfacing with a master device is shown below.
+
++---------------------+                +---------------------+
+|                     |-----SCK------->|CLK                  |
+|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
+|                     |-----SD0------->|D0                   |
+|                     |-----SD1------->|D1                   |
++---------------------+                +---------------------+
+
+As per datasheet, each DRIF channel (drifn) is made up of two internal
+channels (drifn0 & drifn1). These two internal channels share the common
+CLK & SYNC. Each internal channel has its own dedicated resources like
+irq, dma channels, address space & clock. This internal split is not
+visible to the external master device.
+
+The device tree model represents each internal channel as a separate node.
+The internal channels sharing the CLK & SYNC are tied together by their
+phandles using a property called "renesas,bonding". For the rest of
+the documentation, unless explicitly stated, the word channel implies an
+internal channel.
+
+When both internal channels are enabled they need to be managed together
+as one (i.e.) they cannot operate alone as independent devices. Out of the
+two, one of them needs to act as a primary device that accepts common
+properties of both the internal channels. This channel is identified by a
+property called "renesas,primary-bond".
+
+To summarize,
+   - When both the internal channels that are bonded together are enabled,
+     the zeroth channel is selected as primary-bond. This channels accepts
+     properties common to all the members of the bond.
+   - When only one of the bonded channels need to be enabled, the property
+     "renesas,bonding" or "renesas,primary-bond" will have no effect. That
+     enabled channel can act alone as any other independent device.
+
+Required properties of an internal channel:
+-------------------------------------------
+- compatible:	"renesas,r8a7795-drif" if DRIF controller is a part of R8A7795 SoC.
+		"renesas,rcar-gen3-drif" for a generic R-Car Gen3 compatible device.
+
+		When compatible with the generic version, nodes must list the
+		SoC-specific version corresponding to the platform first
+		followed by the generic version.
+
+- reg: offset and length of that channel.
+- interrupts: associated with that channel.
+- clocks: phandle and clock specifier of that channel.
+- clock-names: clock input name string: "fck".
+- dmas: phandles to the DMA channels.
+- dma-names: names of the DMA channel: "rx".
+- renesas,bonding: phandle to the other channel.
+
+Optional properties of an internal channel:
+-------------------------------------------
+- power-domains: phandle to the respective power domain.
+
+Required properties of an internal channel when:
+	- It is the only enabled channel of the bond (or)
+	- If it acts as primary among enabled bonds
+--------------------------------------------------------
+- pinctrl-0: pin control group to be used for this channel.
+- pinctrl-names: must be "default".
+- renesas,primary-bond: empty property indicating the channel acts as primary
+			among the bonded channels.
+- port: child port node corresponding to the data input, in accordance with
+	the video interface bindings defined in
+	Documentation/devicetree/bindings/media/video-interfaces.txt. The port
+	node must contain at least one endpoint.
+
+Optional endpoint property:
+---------------------------
+- sync-active: Indicates sync signal polarity, 0/1 for low/high respectively.
+	       This property maps to SYNCAC bit in the hardware manual. The
+	       default is 1 (active high).
+
+Example:
+--------
+
+(1) Both internal channels enabled:
+-----------------------------------
+
+When interfacing with a third party tuner device with two data pins as shown
+below.
+
++---------------------+                +---------------------+
+|                     |-----SCK------->|CLK                  |
+|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
+|                     |-----SD0------->|D0                   |
+|                     |-----SD1------->|D1                   |
++---------------------+                +---------------------+
+
+	drif00: rif@e6f40000 {
+		compatible = "renesas,r8a7795-drif",
+			     "renesas,rcar-gen3-drif";
+		reg = <0 0xe6f40000 0 0x64>;
+		interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cpg CPG_MOD 515>;
+		clock-names = "fck";
+		dmas = <&dmac1 0x20>, <&dmac2 0x20>;
+		dma-names = "rx", "rx";
+		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
+		renesas,bonding = <&drif01>;
+		renesas,primary-bond;
+		pinctrl-0 = <&drif0_pins>;
+		pinctrl-names = "default";
+		port {
+			drif0_ep: endpoint {
+			     remote-endpoint = <&tuner_ep>;
+			};
+		};
+	};
+
+	drif01: rif@e6f50000 {
+		compatible = "renesas,r8a7795-drif",
+			     "renesas,rcar-gen3-drif";
+		reg = <0 0xe6f50000 0 0x64>;
+		interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cpg CPG_MOD 514>;
+		clock-names = "fck";
+		dmas = <&dmac1 0x22>, <&dmac2 0x22>;
+		dma-names = "rx", "rx";
+		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
+		renesas,bonding = <&drif00>;
+	};
+
+
+(2) Internal channel 1 alone is enabled:
+----------------------------------------
+
+When interfacing with a third party tuner device with one data pin as shown
+below.
+
++---------------------+                +---------------------+
+|                     |-----SCK------->|CLK                  |
+|       Master        |-----SS-------->|SYNC  DRIFn (slave)  |
+|                     |                |D0 (unused)          |
+|                     |-----SD-------->|D1                   |
++---------------------+                +---------------------+
+
+	drif00: rif@e6f40000 {
+		compatible = "renesas,r8a7795-drif",
+			     "renesas,rcar-gen3-drif";
+		reg = <0 0xe6f40000 0 0x64>;
+		interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cpg CPG_MOD 515>;
+		clock-names = "fck";
+		dmas = <&dmac1 0x20>, <&dmac2 0x20>;
+		dma-names = "rx", "rx";
+		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
+		renesas,bonding = <&drif01>;
+	};
+
+	drif01: rif@e6f50000 {
+		compatible = "renesas,r8a7795-drif",
+			     "renesas,rcar-gen3-drif";
+		reg = <0 0xe6f50000 0 0x64>;
+		interrupts = <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&cpg CPG_MOD 514>;
+		clock-names = "fck";
+		dmas = <&dmac1 0x22>, <&dmac2 0x22>;
+		dma-names = "rx", "rx";
+		power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
+		renesas,bonding = <&drif00>;
+		pinctrl-0 = <&drif0_pins>;
+		pinctrl-names = "default";
+		port {
+			drif0_ep: endpoint {
+			     remote-endpoint = <&tuner_ep>;
+			     sync-active = <0>;
+			};
+		};
+	};