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

[Du, Bin]

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@xxxxxxx>
> > Signed-off-by: Svetoslav Stoilov <Svetoslav.Stoilov@xxxxxxx>
> > ---
> >   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@xxxxxxx>
> >   L:	linux-media@xxxxxxxxxxxxxxx
> >   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/*