linux-kernel - Re: [PATCH] devicetree: Add video bus switch

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Date:   Fri, 3 Feb 2017 15:07:40 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Pavel Machek <pavel@....cz>
Cc:     robh+dt@...nel.org, devicetree@...r.kernel.org,
        ivo.g.dimitrov.75@...il.com, sre@...nel.org, pali.rohar@...il.com,
        linux-media@...r.kernel.org, galak@...eaurora.org,
        mchehab@....samsung.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] devicetree: Add video bus switch

Hi Pavel,

My apologies for the delays in reviewing. Feel free to ping me in the future
if this happens. :-)

On Fri, Feb 03, 2017 at 01:35:08PM +0100, Pavel Machek wrote:
> 
> N900 contains front and back camera, with a switch between the
> two. This adds support for the switch component, and it is now
> possible to select between front and back cameras during runtime.
> 
> This adds documentation for the devicetree binding.
> 
> Signed-off-by: Sebastian Reichel <sre@...nel.org>
> Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
> Signed-off-by: Pavel Machek <pavel@....cz>
> 
> 
> diff --git a/Documentation/devicetree/bindings/media/video-bus-switch.txt b/Documentation/devicetree/bindings/media/video-bus-switch.txt
> new file mode 100644
> index 0000000..1b9f8e0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/media/video-bus-switch.txt
> @@ -0,0 +1,63 @@
> +Video Bus Switch Binding
> +========================
> +
> +This is a binding for a gpio controlled switch for camera interfaces. Such a
> +device is used on some embedded devices to connect two cameras to the same
> +interface of a image signal processor.
> +
> +Required properties
> +===================
> +
> +compatible	: must contain "video-bus-switch"

How generic is this? Should we have e.g. nokia,video-bus-switch? And if so,
change the file name accordingly.

> +switch-gpios	: GPIO specifier for the gpio, which can toggle the
> +		  selected camera. The GPIO should be configured, so
> +		  that a disabled GPIO means, that the first port is
> +		  selected.
> +
> +Required Port nodes
> +===================
> +
> +More documentation on these bindings is available in
> +video-interfaces.txt in the same directory.
> +
> +reg		: The interface:
> +		  0 - port for image signal processor
> +		  1 - port for first camera sensor
> +		  2 - port for second camera sensor

I'd say this must be pretty much specific to the one in N900. You could have
more ports. Or you could say that ports beyond 0 are camera sensors. I guess
this is good enough for now though, it can be changed later on with the
source if a need arises.

Btw. was it still considered a problem that the endpoint properties for the
sensors can be different? With the g_routing() pad op which is to be added,
the ISP driver (should actually go to a framework somewhere) could parse the
graph and find the proper endpoint there.

I don't think we need to wait for that now, but this is how the problem
could be solved going forward.

> +
> +Example
> +=======
> +
> +video-bus-switch {
> +	compatible = "video-bus-switch"
> +	switch-gpios = <&gpio1 1 GPIO_ACTIVE_HIGH>;
> +
> +	ports {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		port@0 {
> +			reg = <0>;
> +
> +			csi_switch_in: endpoint {
> +				remote-endpoint = <&csi_isp>;
> +			};
> +		};
> +
> +		port@1 {
> +			reg = <1>;
> +
> +			csi_switch_out1: endpoint {
> +				remote-endpoint = <&csi_cam1>;
> +			};
> +		};
> +
> +		port@2 {
> +			reg = <2>;
> +
> +			csi_switch_out2: endpoint {
> +				remote-endpoint = <&csi_cam2>;
> +			};
> +		};
> +	};
> +};
> 
> 
> 

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk