linux-kernel - Re: [PATCH v7 2/6] media: admin-guide: Add starfive

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Message-ID: <a108084b-8044-fe6f-9cb8-df1f3fc6fdfe@linaro.org>
Date:   Wed, 26 Jul 2023 12:26:18 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Jack Zhu <jack.zhu@...rfivetech.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Foss <rfoss@...nel.org>,
        Todor Tomov <todor.too@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Eugen Hristev <eugen.hristev@...labora.com>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, changhuang.liang@...rfivetech.com
Subject: Re: [PATCH v7 2/6] media: admin-guide: Add starfive_camss.rst for
 Starfive Camera Subsystem

On 19/06/2023 12:28, Jack Zhu wrote:
> Add starfive_camss.rst file that documents the Starfive Camera
> Subsystem driver which is used for handing image sensor data.
> 
> Signed-off-by: Jack Zhu <jack.zhu@...rfivetech.com>
> ---
>   .../admin-guide/media/starfive_camss.rst      | 57 +++++++++++++++++++
>   .../media/starfive_camss_graph.dot            | 16 ++++++
>   .../admin-guide/media/v4l-drivers.rst         |  1 +
>   MAINTAINERS                                   |  1 +
>   4 files changed, 75 insertions(+)
>   create mode 100644 Documentation/admin-guide/media/starfive_camss.rst
>   create mode 100644 Documentation/admin-guide/media/starfive_camss_graph.dot
> 
> diff --git a/Documentation/admin-guide/media/starfive_camss.rst b/Documentation/admin-guide/media/starfive_camss.rst
> new file mode 100644
> index 000000000000..a6378849384f
> --- /dev/null
> +++ b/Documentation/admin-guide/media/starfive_camss.rst
> @@ -0,0 +1,57 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +.. include:: <isonum.txt>
> +
> +================================
> +Starfive Camera Subsystem driver
> +================================
> +
> +Introduction
> +------------
> +
> +This file documents the driver for the Starfive Camera Subsystem found on
> +Starfive JH7110 SoC. The driver is located under drivers/media/platform/
> +starfive.
> +
> +The driver implements V4L2, Media controller and v4l2_subdev interfaces.
> +Camera sensor using V4L2 subdev interface in the kernel is supported.
> +
> +The driver has been successfully used on the Gstreamer 1.18.5 with
> +v4l2src plugin.
> +
> +
> +Starfive Camera Subsystem hardware
> +----------------------------------
> +
> +The Starfive Camera Subsystem hardware consists of:
> +
> +- MIPI DPHY Receiver: receives mipi data from a MIPI camera sensor.

Feels like a terribe nit-pick but you have "mipi" and "MIPI" here. I'd 
be consistent with one - recommend MIPI throughout your documentation.

> +- MIPI CSIRx Controller: is responsible for handling and decoding CSI2 protocol
> +  based camera sensor data stream.
> +- ISP: handles the image data streams from the MIPI CSIRx Controller.

Maybe you've done this elsewhere but, it would be worthwhile describing 
what the ISP does. Debayering ? 3As ? Just raw dumps ?

> +- VIN(Video In): a top-level module, is responsible for controlling power
> +  and clocks to other modules, dumps the input data to memory or transfers the
> +  input data to ISP.
> +
> +
> +Topology
> +--------
> +
> +The media controller pipeline graph is as follows:
> +
> +.. _starfive_camss_graph:
> +
> +.. kernel-figure:: starfive_camss_graph.dot
> +    :alt:   starfive_camss_graph.dot
> +    :align: center
> +
> +The driver has 2 video devices:
> +
> +- stf_vin0_wr_video0: capture device for images directly from the VIN module.

OK so you can get the raw images.

> +- stf_vin0_isp0_video1: capture device for images without scaling.
> +
> +The driver has 3 subdevices:
> +
> +- stf_isp0: is responsible for all the isp operations.
> +- stf_vin0_wr: used to dump RAW images to memory.
> +- stf_vin0_isp0: used to capture images for the stf_vin0_isp0_video1 device.

But what is being output here ? RGB, jpeg, YUV ?
It would be worth adding a few bits of text to describe that so you 
don't have to dive into code to understand it.

---
bod