linux-kernel - Re: [PATCH v2 8/8] Documentation: add documentation of AMD isp 4 driver

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Message-ID: <20250805113719.GF24627@pendragon.ideasonboard.com>
Date: Tue, 5 Aug 2025 14:37:19 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Bin Du <Bin.Du@....com>
Cc: mchehab@...nel.org, hverkuil@...all.nl, bryan.odonoghue@...aro.org,
	sakari.ailus@...ux.intel.com,
	prabhakar.mahadev-lad.rj@...renesas.com,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	pratap.nirujogi@....com, benjamin.chan@....com, king.li@....com,
	gjorgji.rosikopulos@....com, Phil.Jawich@....com,
	Dominic.Antony@....com, Svetoslav.Stoilov@....com
Subject: Re: [PATCH v2 8/8] Documentation: add documentation of AMD isp 4
 driver

On Wed, Jun 18, 2025 at 05:19:59PM +0800, Bin Du wrote:
> Add documentation for AMD isp 4 and describe the main components
> 
> Signed-off-by: Bin Du <Bin.Du@....com>
> Signed-off-by: Svetoslav Stoilov <Svetoslav.Stoilov@....com>
> ---
>  Documentation/admin-guide/media/amdisp4-1.rst | 64 +++++++++++++++++++
>  Documentation/admin-guide/media/amdisp4.dot   |  8 +++
>  MAINTAINERS                                   |  2 +
>  3 files changed, 74 insertions(+)
>  create mode 100644 Documentation/admin-guide/media/amdisp4-1.rst
>  create mode 100644 Documentation/admin-guide/media/amdisp4.dot
> 
> diff --git a/Documentation/admin-guide/media/amdisp4-1.rst b/Documentation/admin-guide/media/amdisp4-1.rst
> new file mode 100644
> index 000000000000..417b15af689a
> --- /dev/null
> +++ b/Documentation/admin-guide/media/amdisp4-1.rst
> @@ -0,0 +1,64 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +.. include:: <isonum.txt>
> +
> +====================================
> +AMD Image Signal Processor (amdisp4)
> +====================================
> +
> +Introduction
> +============
> +
> +This file documents the driver for the AMD ISP4 that is part of
> +AMD Ryzen AI Max 385 SoC.
> +
> +The driver is located under drivers/media/platform/amd/isp4 and uses
> +the Media-Controller API.
> +
> +Topology
> +========
> +
> +.. _amdisp4_topology_graph:
> +
> +.. kernel-figure:: amdisp4.dot
> +     :alt:   Diagram of the media pipeline topology
> +     :align: center
> +
> +
> +
> +The driver has 1 sub-device:
> +
> +- isp: used to resize and process bayer raw frames in to yuv.
> +
> +The driver has 1 video device:
> +
> +- <capture video device: capture device for retrieving images.
> +
> +
> +  - ISP4 Image Signal Processing Subdevice Node
> +-----------------------------------------------
> +
> +The isp4 is represented as a single V4L2 subdev, the sub-device does not
> +provide interface to the user space.

Doesn't it ? The driver sets the V4L2_SUBDEV_FL_HAS_DEVNODE flag for the
subdev, and calls v4l2_device_register_subdev_nodes().

As far as I understand, the camera is exposed by the firmware with a
webcam-like interface. We need to better understand your plans with this
driver. If everything is handled by the firmware, why are the sensor and
subdev exposed to userspace ? Why can't you expose a single video
capture device, with a media device, and handle everything behind the
scene ? I assume there may be more features coming later. Please
document the plan, we can't provide feedback on the architecture
otherwise.

> The sub-device is connected to one video node
> +(isp4_capture) with immutable active link. The isp entity is connected
> +to sensor pad 0 and receives the frames using CSI-2 protocol. The sub-device is
> +also responsible to configure CSI2-2 receiver.
> +The sub-device processes bayer raw data from the connected sensor and output
> +them to different YUV formats. The isp also has scaling capabilities.
> +
> +  - isp4_capture - Frames Capture Video Node
> +--------------------------------------------
> +
> +Isp4_capture is a capture device to capture frames to memory.
> +This entity is the DMA engine that write the frames to memory.
> +The entity is connected to isp4 sub-device.
> +
> +Capturing Video Frames Example
> +==============================
> +
> +.. code-block:: bash
> +
> +         # set the links

This seems very under-documented.

> +
> +         # start streaming:
> +         v4l2-ctl "-d" "/dev/video0" "--set-fmt-video=width=1920,height=1080,pixelformat=NV12" "--stream-mmap" "--stream-count=10"
> diff --git a/Documentation/admin-guide/media/amdisp4.dot b/Documentation/admin-guide/media/amdisp4.dot
> new file mode 100644
> index 000000000000..a4c2f0cceb30
> --- /dev/null
> +++ b/Documentation/admin-guide/media/amdisp4.dot
> @@ -0,0 +1,8 @@
> +digraph board {
> +	rankdir=TB
> +	n00000001 [label="{{<port0> 0} | amd isp4\n | {<port1> 1}}", shape=Mrecord, style=filled, fillcolor=green]
> +	n00000001:port1 -> n00000004 [style=bold]
> +	n00000004 [label="Preview\n/dev/video0", shape=box, style=filled, fillcolor=yellow]
> +	n0000000a [label="{{} | ov05c10 22-0010\n/dev/v4l-subdev0 | {<port0> 0}}", shape=Mrecord, style=filled, fillcolor=green]
> +	n0000000a:port0 -> n00000001:port0 [style=bold]
> +}
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 15070afb14b5..e4455bde376f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -1113,6 +1113,8 @@ M:	Nirujogi Pratap <pratap.nirujogi@....com>
>  L:	linux-media@...r.kernel.org
>  S:	Maintained
>  T:	git git://linuxtv.org/media.git
> +F:	Documentation/admin-guide/media/amdisp4-1.rst
> +F:	Documentation/admin-guide/media/amdisp4.dot
>  F:	drivers/media/platform/amd/Kconfig
>  F:	drivers/media/platform/amd/Makefile
>  F:	drivers/media/platform/amd/isp4/*

-- 
Regards,

Laurent Pinchart