Re: [PATCH v12 1/2] rcar-csi2: add Renesas R-Car MIPI CSI-2 receiver documentation

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Niklas,

Thank you for the patch.

On Wednesday, 29 November 2017 21:32:34 EET Niklas Söderlund wrote:
> Documentation for Renesas R-Car MIPI CSI-2 receiver. The CSI-2 receivers
> are located between the video sources (CSI-2 transmitters) and the video
> grabbers (VIN) on Gen3 of Renesas R-Car SoC.
> 
> Each CSI-2 device is connected to more then one VIN device which

s/then/than/

> simultaneously can receive video from the same CSI-2 device. Each VIN
> device can also be connected to more then one CSI-2 device. The routing

s/then/than/

> of which link are used are controlled by the VIN devices. There are only

s/link are/links are/ or s/link are/link is/
s/are controlled/is controlled/

> a few possible routes which are set by hardware limitations, which are
> different for each SoC in the Gen3 family.
> 
> To work with the limitations of routing possibilities it is necessary
> for the DT bindings to describe which VIN device is connected to which
> CSI-2 device. This is why port 1 needs to to assign reg numbers for each
> VIN device that be connected to it. To setup and to know which links are

s/that be/that is/

> valid for each SoC is the responsibility of the VIN driver since the
> register to configure it belongs to the VIN hardware.
> 
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
> Acked-by: Rob Herring <robh@kernel.org>
> ---
>  .../bindings/media/renesas,rcar-csi2.txt           | 105 ++++++++++++++++++
>  MAINTAINERS                                        |   1 +
>  2 files changed, 106 insertions(+)
>  create mode 100644
> Documentation/devicetree/bindings/media/renesas,rcar-csi2.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/renesas,rcar-csi2.txt
> b/Documentation/devicetree/bindings/media/renesas,rcar-csi2.txt new file
> mode 100644
> index 0000000000000000..688afd83bf66f8cf
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/renesas,rcar-csi2.txt
> @@ -0,0 +1,105 @@
> +Renesas R-Car MIPI CSI-2
> +------------------------
> +
> +The rcar-csi2 device provides MIPI CSI-2 capabilities for the Renesas R-Car

rcar-csi2 is the name of the driver, I would call it the "R-Car CSI-2 receiver 
device" (or s/device/IP core/).

> +family of devices. It is to be used in conjunction with the R-Car VIN
> module,

The IP core itself doesn't have to be used with the VIN, but in R-Car SoCs it 
is, so I would phrase it as "It is used ...".

> +which provides the video capture capabilities.
> +
> +Mandatory properties
> +--------------------
> + - compatible: Must be one or more of the following
> +   - "renesas,r8a7795-csi2" for the R8A7795 device.
> +   - "renesas,r8a7796-csi2" for the R8A7796 device.
> +
> + - reg: the register base and size for the device registers
> + - interrupts: the interrupt for the device
> + - clocks: Reference to the parent clock

Either capitalize the first word after the colon or don't, but please don't 
mix them :-)

> +
> +The device node shall contain two 'port' child nodes according to the
> +bindings defined in Documentation/devicetree/bindings/media/
> +video-interfaces.txt. Port 0 shall connect the node that is the video
> +source for to the CSI-2.

Or simply "Port 0 shall connect to the CSI-2 source." ?

> Port 1 shall connect all the R-Car VIN
> +modules, which can make use of the CSI-2 module.

And to be a bit more explicit, how about "Port 1 shall connect to all the R-
Car VIN modules that have a hardware connection to the CSI-2 receiver." ?

> +
> +- Port 0 - Video source (Mandatory)

Nitpicking, I don't think you need to capitalize Mandatory.

> +	- Endpoint 0 - sub-node describing the endpoint that is the video source
> +
> +- Port 1 - VIN instances (Mandatory for all VIN present in the SoC)
> +	- Endpoint 0 - sub-node describing the endpoint that is VIN0
> +	- Endpoint 1 - sub-node describing the endpoint that is VIN1
> +	- Endpoint 2 - sub-node describing the endpoint that is VIN2
> +	- Endpoint 3 - sub-node describing the endpoint that is VIN3
> +	- Endpoint 4 - sub-node describing the endpoint that is VIN4
> +	- Endpoint 5 - sub-node describing the endpoint that is VIN5
> +	- Endpoint 6 - sub-node describing the endpoint that is VIN6
> +	- Endpoint 7 - sub-node describing the endpoint that is VIN7

Should we clarify that only a subset of those endpoints shall be present when 
the CSI-2 receiver isn't connected to all VIN instances ?

Furthermore, as explained in a comment I made when reviewing the VIN patch 
series, I wonder whether we shouldn't identify the CSI-2 receiver instances by 
ID the same way we do with the VIN instances (using the renesas,id property). 
In that case I think the endpoint numbering won't matter.

> +Example:
> +
> +	csi20: csi2@fea80000 {
> +		compatible = "renesas,r8a7796-csi2";
> +		reg = <0 0xfea80000 0 0x10000>;
> +		interrupts = <0 184 IRQ_TYPE_LEVEL_HIGH>;
> +		clocks = <&cpg CPG_MOD 714>;
> +		power-domains = <&sysc R8A7796_PD_ALWAYS_ON>;
> +		resets = <&cpg 714>;
> +
> +		ports {
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +
> +			port@0 {
> +				#address-cells = <1>;
> +				#size-cells = <0>;
> +
> +				reg = <0>;
> +
> +				csi20_in: endpoint@0 {
> +					reg = <0>;
> +					clock-lanes = <0>;
> +					data-lanes = <1>;
> +					remote-endpoint = <&adv7482_txb>;
> +				};
> +			};
> +
> +			port@1 {
> +				#address-cells = <1>;
> +				#size-cells = <0>;
> +
> +				reg = <1>;
> +
> +				csi20vin0: endpoint@0 {
> +					reg = <0>;
> +					remote-endpoint = <&vin0csi20>;
> +				};
> +				csi20vin1: endpoint@1 {
> +					reg = <1>;
> +					remote-endpoint = <&vin1csi20>;
> +				};
> +				csi20vin2: endpoint@2 {
> +					reg = <2>;
> +					remote-endpoint = <&vin2csi20>;
> +				};
> +				csi20vin3: endpoint@3 {
> +					reg = <3>;
> +					remote-endpoint = <&vin3csi20>;
> +				};
> +				csi20vin4: endpoint@4 {
> +					reg = <4>;
> +					remote-endpoint = <&vin4csi20>;
> +				};
> +				csi20vin5: endpoint@5 {
> +					reg = <5>;
> +					remote-endpoint = <&vin5csi20>;
> +				};
> +				csi20vin6: endpoint@6 {
> +					reg = <6>;
> +					remote-endpoint = <&vin6csi20>;
> +				};
> +				csi20vin7: endpoint@7 {
> +					reg = <7>;
> +					remote-endpoint = <&vin7csi20>;
> +				};
> +			};
> +		};
> +	};
> diff --git a/MAINTAINERS b/MAINTAINERS
> index aa71ab52fd76d160..4737de9f41bff570 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8652,6 +8652,7 @@ L:	linux-media@vger.kernel.org
>  L:	linux-renesas-soc@vger.kernel.org
>  T:	git git://linuxtv.org/media_tree.git
>  S:	Supported
> +F:	Documentation/devicetree/bindings/media/renesas,rcar-csi2.txt
>  F:	Documentation/devicetree/bindings/media/rcar_vin.txt
>  F:	drivers/media/platform/rcar-vin/

-- 
Regards,

Laurent Pinchart