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

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Message-ID: <20230727102328.GE5148@pendragon.ideasonboard.com>
Date:   Thu, 27 Jul 2023 13:23:28 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     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>,
        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

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".

> > +- MIPI CSIRx Controller: is responsible for handling and decoding CSI2 protocol

It's "CSI-2", not "CSI2".

> > +  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).

> > +
> > +
> > +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,

Laurent Pinchart