linux-kernel - Re: [PATCH v2 2/2] [media] atmel-isc: DT binding for Image Sensor Controller driver

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Date:	Wed, 18 May 2016 18:05:22 -0500
From:	Rob Herring <robh@...nel.org>
To:	Songjun Wu <songjun.wu@...el.com>
Cc:	g.liakhovetski@....de, laurent.pinchart@...asonboard.com,
	nicolas.ferre@...el.com, linux-arm-kernel@...ts.infradead.org,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] [media] atmel-isc: DT binding for Image Sensor
 Controller driver

On Wed, May 18, 2016 at 03:46:29PM +0800, Songjun Wu wrote:
> DT binding documentation for ISC driver.
> 
> Signed-off-by: Songjun Wu <songjun.wu@...el.com>
> ---
> 
> Changes in v2:
> - Remove the unit address of the endpoint.
> - Add the unit address to the clock node.
> - Avoid using underscores in node names.
> - Drop the "0x" in the unit address of the i2c node.
> - Modify the description of "atmel,sensor-preferred".
> - Add the description for the ISC internal clock.
> 
>  .../devicetree/bindings/media/atmel-isc.txt        | 100 +++++++++++++++++++++
>  1 file changed, 100 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/atmel-isc.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/atmel-isc.txt b/Documentation/devicetree/bindings/media/atmel-isc.txt
> new file mode 100644
> index 0000000..9e65395
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/atmel-isc.txt
> @@ -0,0 +1,100 @@
> +Atmel Image Sensor Controller (ISC)
> +----------------------------------------------
> +
> +Required properties for ISC:
> +- compatible
> +	Must be "atmel,sama5d2-isc"
> +- reg
> +	Physical base address and length of the registers set for the device;
> +- interrupts
> +	Should contain IRQ line for the ISC;
> +- clocks
> +	List of clock specifiers, corresponding to entries in
> +	the clock-names property;
> +	Please refer to clock-bindings.txt.
> +- clock-names
> +	Required elements: "hclock", "ispck".
> +- pinctrl-names, pinctrl-0
> +	Please refer to pinctrl-bindings.txt.
> +- clk-in-isc
> +	ISC internal clock node, it includes two clock nodes,
> +	isc-ispck and isc-mck.

And you need to describe each of these nodes and the properties they 
have. But more on this below...

> +- atmel,sensor-preferred
> +	ISC may convert the raw format to the specified format when the sensor
> +	outputs the raw format, and the sensor may output the specified format
> +	directly. If sensor is preferred to output the specified format
> +	directly, the value should be 1 (1-preferred, 0-not).
> +	The default value is 1.

I don't think this belongs in DT. It sounds more like a configuration 
and userspace decision. It is still not clear what you mean by 
"specified format".

> +
> +ISC supports a single port node with parallel bus. It should contain one
> +'port' child node with child 'endpoint' node. Please refer to the bindings
> +defined in Documentation/devicetree/bindings/media/video-interfaces.txt.
> +
> +Required properties for the ISC internal clocks:
> +- #address-cells
> +	should be 1 (reg is used to encode clk id).
> +- #size-cells
> +	should be 0 (reg is used to encode clk id).
> +- name
> +	device tree node describing a ISC internal clock.
> +	* #clock-cells: from common clock binding; should be set to 0.
> +	* reg: clock id, there are two values,
> +	       <0> is ISP clock, <1> is master clock.
> +	* clocks: shall be the isc internal clock source phandles.
> +		  e.g. clocks = <&isc_clk>, <&iscck>, <&isc_gclk>;
> +
> +Example:
> +isc: isc@...08000 {
> +	compatible = "atmel,sama5d2-isc";
> +	reg = <0xf0008000 0x4000>;
> +	interrupts = <46 IRQ_TYPE_LEVEL_HIGH 5>;
> +	clocks = <&isc_clk>, <&isc_ispck>;
> +	clock-names = "hclock", "ispck";
> +	atmel,sensor-preferred = <1>;
> +
> +	port {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		isc_0: endpoint {
> +			remote-endpoint = <&ov7740_0>;
> +			hsync-active = <1>;
> +			vsync-active = <0>;
> +			pclk-sample = <1>;
> +		};
> +	};
> +
> +	clk-in-isc {

Is this really separate from the rest of the isc block. It would be 
much more simple to define all the input clocks at the parent and then 
reference these 2 clocks with <&isc 0> and <&isc 1>.

> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		isc_ispck: isc-ispck@0 {

These would need a compatible string otherwise.

> +			#clock-cells = <0>;
> +			reg = <0>;

Are 0 and 1 meaningful in terms of the hardware description?

> +			clocks = <&isc_clk>, <&iscck>;
> +		};
> +
> +		isc_mck: isc-mck@1 {
> +			#clock-cells = <0>;
> +			reg = <1>;
> +			clocks = <&isc_clk>, <&iscck>, <&isc_gclk>;
> +		};
> +	};
> +};