Re: [PATCH 1/3] media: dt-bindings: add bindings for Toshiba TC358746

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Marco,

My apologies for reviewing this so late. You've received good comments
already. I have a few more.

On Tue, Dec 18, 2018 at 03:12:38PM +0100, Marco Felsch wrote:
> Add corresponding dt-bindings for the Toshiba tc358746 device.
> 
> Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
> ---
>  .../bindings/media/i2c/toshiba,tc358746.txt   | 80 +++++++++++++++++++
>  1 file changed, 80 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.txt
> 
> diff --git a/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.txt b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.txt
> new file mode 100644
> index 000000000000..499733df744a
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/i2c/toshiba,tc358746.txt
> @@ -0,0 +1,80 @@
> +* Toshiba TC358746 Parallel to MIPI CSI2-TX or MIPI CSI2-RX to Parallel Bridge
> +
> +The Toshiba TC358746 is a bridge that converts a Parallel-in stream to MIPI CSI-2 TX
> +or a MIPI CSI-2 RX stream into a Parallel-out. It is programmable through I2C.

This is interesting. The driver somehow needs to figure out the direction
of the data flow if it does not originate from DT. I guess it shouldn't as
it's not the property of an individual device, albeit in practice in all
hardware I've seen the direction of the pipeline is determinable and this
is visible in the kAPI as well. So I'm suggesting no changes due to this in
bindings, likely we'll need to address it somehow elsewhere going forward.

> +
> +Required Properties:
> +
> +- compatible: should be "toshiba,tc358746"
> +- reg: should be <0x0e>
> +- clocks: should contain a phandle link to the reference clock source
> +- clock-names: the clock input is named "refclk".
> +
> +Optional Properties:
> +
> +- reset-gpios: gpio phandle GPIO connected to the reset pin
> +
> +Parallel Endpoint:
> +
> +Required Properties:

It'd be nice if the relation between these sections would be somehow
apparent. E.g. using different underlining, such as in
Documentation/devicetree/bindings/media/ti,omap3isp.txt .

> +
> +- reg: should be <0>
> +- bus-width: the data bus width e.g. <8> for eight bit bus, or <16>
> +	     for sixteen bit wide bus.
> +
> +MIPI CSI-2 Endpoint:
> +
> +Required Properties:
> +
> +- reg: should be <1>
> +- data-lanes: should be <1 2 3 4> for four-lane operation,
> +	      or <1 2> for two-lane operation
> +- clock-lanes: should be <0>
> +- link-frequencies: List of allowed link frequencies in Hz. Each frequency is
> +		    expressed as a 64-bit big-endian integer. The frequency
> +		    is half of the bps per lane due to DDR transmission.
> +
> +Optional Properties:
> +
> +- clock-noncontinuous: Presence of this boolean property decides whether the
> +		       MIPI CSI-2 clock is continuous or non-continuous.
> +
> +For further information on the endpoint node properties, see
> +Documentation/devicetree/bindings/media/video-interfaces.txt.
> +
> +Example:
> +
> +&i2c {
> +	tc358746: tc358746@0e {

The node name should be a generic name of the type of the device, not the
name of the specific device as such. A similar Cadence device uses
"csi-bridge".

> +		reg = <0x0e>;
> +		compatible = "toshiba,tc358746";
> +		pinctrl-names = "default";
> +		clocks = <&clk_cam_ref>;
> +		clock-names = "refclk";
> +		reset-gpios = <&gpio3 2 GPIO_ACTIVE_LOW>;
> +
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@0 {
> +			reg = <0>;
> +
> +			tc358746_parallel_in: endpoint {
> +				bus-width = <8>;
> +				remote-endpoint = <&micron_parallel_out>;
> +			};
> +		};
> +
> +		port@1 {
> +			reg = <1>;
> +
> +			tc358746_mipi2_out: endpoint {
> +				remote-endpoint = <&mipi_csi2_in>;
> +				data-lanes = <1 2>;
> +				clock-lanes = <0>;
> +				clock-noncontinuous;
> +				link-frequencies = /bits/ 64 <216000000>;
> +			};
> +		};
> +	};
> +};

-- 
Kind regards,

Sakari Ailus
sakari.ailus@linux.intel.com