Re: [PATCH v7 2/6] media: admin-guide: Add starfive_camss.rst for Starfive Camera Subsystem

Laurent Pinchart
2023-07-27T10:23:40Z

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@starfivetech.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