Re: [PATCH v10 24/64] media: uapi: ccs: Add metadata layout for MIPI CCS embedded data

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi Sakari

On Tue, Jan 13, 2026 at 11:32:18PM +0200, Sakari Ailus wrote:
> Hi Jacopo,
>
> On Fri, Jun 20, 2025 at 03:24:09PM +0200, Jacopo Mondi wrote:
> > Hi Sakari
> >
> > On Thu, Jun 19, 2025 at 02:57:56PM +0300, Sakari Ailus wrote:
> > > Add new metadata layout (V4L2_METADATA_LAYOUT_CCS) for MIPI CCS embedded
> > > data.
> > >
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > Reviewed-by: Julien Massot <julien.massot@collabora.com>
> > > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > ---
> > >  .../userspace-api/media/v4l/meta-formats.rst  |  1 +
> > >  .../media/v4l/metadata-layouts.rst            | 39 +++++++++++++++++++
> > >  .../media/v4l/subdev-formats.rst              |  5 +++
> > >  include/uapi/linux/v4l2-controls.h            |  1 +
> > >  4 files changed, 46 insertions(+)
> > >  create mode 100644 Documentation/userspace-api/media/v4l/metadata-layouts.rst
> > >
> > > diff --git a/Documentation/userspace-api/media/v4l/meta-formats.rst b/Documentation/userspace-api/media/v4l/meta-formats.rst
> > > index bb6876cfc271..c9b908d5fbea 100644
> > > --- a/Documentation/userspace-api/media/v4l/meta-formats.rst
> > > +++ b/Documentation/userspace-api/media/v4l/meta-formats.rst
> > > @@ -15,6 +15,7 @@ These formats are used for the :ref:`metadata` interface only.
> > >      metafmt-c3-isp
> > >      metafmt-d4xx
> > >      metafmt-generic
> > > +    metadata-layouts
> > >      metafmt-intel-ipu3
> > >      metafmt-pisp-be
> > >      metafmt-pisp-fe
> > > diff --git a/Documentation/userspace-api/media/v4l/metadata-layouts.rst b/Documentation/userspace-api/media/v4l/metadata-layouts.rst
> > > new file mode 100644
> > > index 000000000000..5f717d54d1ca
> > > --- /dev/null
> > > +++ b/Documentation/userspace-api/media/v4l/metadata-layouts.rst
> > > @@ -0,0 +1,39 @@
> > > +.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
> > > +
> > > +.. _media_metadata_layouts:
> > > +
> > > +Metadata Layouts
> > > +----------------
> > > +
> > > +The :ref:`metadata layout control <image_source_control_metadata_layout>`
> > > +specifies the on-bus layout of the metadata on pads with a :ref:`generic
> > > +metadata mbus code <media-bus-format-generic-meta>` independently of the bit
> > > +depth.
> >
> > This has been reviewed by 2 people already, so it might be not having
> > this clear, but I guess the intention is to say that the metadata
> > layout control describes how data on the bus should be interpreted by
> > userspace while the generic metadata mbus code only defines the sample
> > size ?
>
> Hmm. This should probably refer to Data Unit instead.
>
> Do you think that would help? Bit depth doesn't really apply here.
>

I have a few problems with the text overall, at least as I read it

1) "the metadata layout control specifies the on-bus layout of the
   metadata on pads with a generic metadata mbus code"

This seems to suggest that the control applies on pads with a generic
metadata mbus code

2) "specifies the on-bus layout"

I understand why you used "on-bus" (because we use generic formats on
pads and when the metadata are written to memory, right ?) but I would
rather use "exact layout" or simply "data layout" as you've done below
?

3) I don't get what "on pads with a metadata mbus code indepedently of
the bit depth". What's independent from the bit depth ?

All in all, I guess what I understand is:

The :ref:`metadata layout control <image_source_control_metadata_layout>`
specifies the exact layout of the metadata stream while the a :ref:`generic
metadata mbus code <media-bus-format-generic-meta>` on the subdevice pads
only describe the data unit size.

if that's what you meant

> >
> > I don't really get that from the above paragraph. Feel free to ignore
> > if it's me only :)
>
> --
> Kind regards,
>
> Sakari Ailus