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

Du, Bin
2025-08-12T01:36:24Z

Many thanks Laurent Pinchart for the review.

On 8/5/2025 7:37 PM, Laurent Pinchart wrote:
> 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@amd.com>
>> Signed-off-by: Svetoslav Stoilov <Svetoslav.Stoilov@amd.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().
>

We have exported subdev device to user space during the testing with
libcamera sample pipeline.

> 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.
>

Currently, isp fw is controlling the sensor to update just the exposure
and gain, since the 3A algorithms run on ISP HW rather than on x86. In a
future version, we plan to introduce raw output support in the ISP
driver, allowing users to choose between AMD’s 3A running on ISP
hardware or a custom 3A running on x86. If the user opts for the
x86-based 3A, the firmware will relinquish control of the sensor, and
hands over full control to the x86 system.

>> 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.
>

Yes, documentation needs to be updated.

>> +
>> + # 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@amd.com>
>> L: linux-media@vger.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/*
>