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

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Date:   Mon, 31 Jul 2023 11:39:40 +0800
From:   Jack Zhu <jack.zhu@...rfivetech.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Bryan O'Donoghue <bryan.odonoghue@...aro.org>
CC:     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>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Eugen Hristev <eugen.hristev@...labora.com>,
        Ezequiel Garcia <ezequiel@...guardiasur.com.ar>,
        <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

Hi Laurent,

Thank you for your comments.

On 2023/7/27 18:23, Laurent Pinchart wrote:
> On Wed, Jul 26, 2023 at 12:26:18PM +0100, Bryan O'Donoghue wrote:
>> 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.
> 
> I'd drop the "mipi" and just write "data", not "MIPI data".
> 

Ok, I will modify it.

>> > +- MIPI CSIRx Controller: is responsible for handling and decoding CSI2 protocol
> 
> It's "CSI-2", not "CSI2".

Ok, I will modify it.

> 
>> > +  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.
> 
> A block diagram could be nice. Let me give it a try, based on my
> understanding:
> 
> Starfive Camera Subsystem hardware
> ----------------------------------
> 
> The Starfive Camera Subsystem hardware consists of::
> 
>                 +---------------------------------------------+
>                 | VIN                                         |
>   +--------+    | +-------+   +-------+    +-----+            |
>   | Camera |----->| D-PHY |-->| CSI-2 |-+->| DMA |            |
>   | Sensor |    | |  RX   |   |  RX   | |  +-----+            |
>   +--------+    | +-------+   +-------+ |                     |
>                 |                       |  +-----+   +-----+  |
>                 |                       \->| ISP |-->| DMA |  |
>                 |                          +-----+   +-----+  |
>                 +---------------------------------------------+
> 
> - VIN (Video IN): The top-level module, responsible for controlling
>   power and clocks, and routing data between modules.
> 
> - D-PHY RX: The MIPI D-PHY receiver, receiving data from a MIPI CSI-2
>   camera sensor.
> 
> - CSI-2 RX: The MIPI CSI-2 receiver controller, responsible for decoding
>   the CSI-2 protocol.
> 
> - ISP: The ISP, processing raw Bayer data from the CSI-2 receiver and
>   producing YUV frames.
> 
> 
> I haven't tried compiling this, so please fix formatting if anything is
> wrong (and of course feel free to adapt the diagram and text).
> 

Ok, I will add a block diagram.

>> > +
>> > +
>> > +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.
> 

-- 
Regards,

Jack Zhu