linux-kernel - Re: [PATCH v4 04/21] doc: media/v4l-drivers: Add Qualcomm Camera Subsystem driver document

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Date:   Fri, 25 Aug 2017 16:10:51 +0200
From:   Daniel Mack <daniel@...que.org>
To:     Todor Tomov <todor.tomov@...aro.org>, mchehab@...nel.org,
        hans.verkuil@...co.com, s.nawrocki@...sung.com,
        sakari.ailus@....fi, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 04/21] doc: media/v4l-drivers: Add Qualcomm Camera
 Subsystem driver document

Hi Todor,

Thanks a lot for working on the upstream support for this!

On 08/08/2017 03:30 PM, Todor Tomov wrote:
> +The Camera Subsystem hardware found on 8x16 processors and supported by the
> +driver consists of:
> +
> +- 2 CSIPHY modules. They handle the Physical layer of the CSI2 receivers.
> +  A separate camera sensor can be connected to each of the CSIPHY module;
> +- 2 CSID (CSI Decoder) modules. They handle the Protocol and Application layer
> +  of the CSI2 receivers. A CSID can decode data stream from any of the CSIPHY.
> +  Each CSID also contains a TG (Test Generator) block which can generate
> +  artificial input data for test purposes;
> +- ISPIF (ISP Interface) module. Handles the routing of the data streams from
> +  the CSIDs to the inputs of the VFE;
> +- VFE (Video Front End) module. Contains a pipeline of image processing hardware
> +  blocks. The VFE has different input interfaces. The PIX input interface feeds
> +  the input data to the image processing pipeline. Three RDI input interfaces
> +  bypass the image processing pipeline. The VFE also contains the AXI bus
> +  interface which writes the output data to memory.

[I'm based on the 4.9 Linaro downstream version of this code right now,
but at a glance the driver version there looks very much identical to
this one.]

Could you explain how ISPIF, CSID and CSIPHY are related?

I have a userspace test setup that works fine for USB webcams, but when
operating on any of the video devices exposed by this driver, the
lowlevel functions such as .s_power of the ISPIF, CSID, CSIPHY and the
sensor driver layers aren't called into.

The general setup seems to work fine though. The sensor is probed,
camss_subdev_notifier_complete() is called, and the v4l2 subdevices
exist. But the stream start is not propagated to the other layers, and
I'm trying to understand why.

My DTS looks something like this right now, and the hardware is an
APQ8016 board (Variscite DART SD410).

&i2c {
	cam0: ov5640@3c {
		compatible = "ovti,ov5640";
		reg = <0x3c>;

		// clocks, regulators, gpios etc are omitted

		port {
			cam0_ep: endpoint {
				clock-lanes = <1>;
				data-lanes = <0 2>;
				remote-endpoint = <&csiphy0_ep>;
			};
		};
	};
};

&camss {
	ports {
		port@0 {
			reg = <0>;
			csiphy0_ep: endpoint {
				clock-lanes = <1>;
				data-lanes = <0 1 2 3>;
				qcom,settle-cnt = <0xe>;
				remote-endpoint = <&cam0_ep>;
			};
		};
	};
};

Also, which video device should be opened when accessing the cameras on
each of the hardware ports? And what are the other two devices doing?

I'm sure I'm missing something trivial, but at least I can't find this
information in the documentation.

Thanks,
Daniel