[v4,00/20] Generic line based metadata support, internal pads

Hi folks,

Here are a few patches to add support generic, line based metadata as well
as internal pads. While the amount of code is not very large, to the
contrary it is quite small actually IMO, I presume what this is about and
why it is being proposed requires some explaining.

Metadata mbus codes and formats have existed for some time in V4L2. They
however have been only used by drivers that produce the data itself and
effectively this metadata has always been statistics of some sort (at
least when it comes to ISPs). What is different here is that we intend to
add support for metadata originating from camera sensors.

Camera sensors produce different kinds of metadata, embedded data (usually
register address--value pairs used to capture the frame, in a more or less
sensor specific format), histograms (in a very sensor specific format),
dark pixels etc. The number of these formats is probably going to be about
as large as image data formats if not larger, as the image data formats
are much better standardised but a smaller subset of them will be
supported by V4L2, at least initially but possibly much more in the long
run.

Having this many device specific formats would be a major problem for all
the other drivers along that pipeline (not to mention the users of those
drivers), including bridge (e.g. CSI-2 to parallel) but especially CSI-2
receiver drivers that have DMA: the poor driver developer would not only
need to know camera sensor specific formats but to choose the specific
packing of that format suitable for the DMA used by the hardware. It is
unlikely many of these would ever get tested while being present on the
driver API. Also adding new sensors with new embedded data formats would
involve updating all bridge and CSI-2 receiver drivers. I don't expect
this to be a workable approach.

Instead what I'm proposing is to use specific metadata formats on the
sensor devices only, on internal pads (more about those soon) of the
sensors, only visible in the UAPI, and then generic mbus formats along the
pipeline and finally generic V4L2 metadata formats on the DMAs (specific
to bit depth and packing). This would unsnarl the two, defining what data
there is (specific mbus code) and how that is transported and packed
(generic mbus codes and V4L2 formats).

The user space would be required to "know" the path of that data from the
sensor's internal pad to the V4L2 video node. I do not see this as these
devices require at least some knowledge of the pipeline, i.e. hardware at
hand. Separating what the data means and how it is packed may even be
beneficial: it allows separating code that interprets the data (sensor
internal mbus code) from the code that accesses it (packing).

These formats are in practice line based, meaning that there may be
padding at the end of the line, depending on the bus as well as the DMA.
If non-line based formats are needed, it is always possible to set the
"height" field to 1.

The internal (source) pads are an alternative to source routes [1]. The
source routes were not universally liked and I do have to say I like
re-using existing interface concepts (pads and everything you can do with
pads, including access format, selections etc.) wherever it makes sense,
instead of duplicating functionality.

Effectively internal source pads behave mostly just like sink pads, but
they describe a flow of data that originates from a sub-device instead of
arriving to a sub-device. The SUBDEV_S_ROUTING IOCTLs are used to enable
and disable routes from internal source pads to sub-device's source pads.
The subdev format IOCTLs are usable, too, so one can find which subdev
format is available on given internal source pad.

This set depends on these patches:

<URL:https://lore.kernel.org/linux-media/20230922115730.251779-1-sakari.ailus@linux.intel.com/T/#t>

I've also pushed these here and I'll keep updating the branch, I've also
included untested OV2740 patches:

<URL:https://git.linuxtv.org/sailus/media_tree.git/log/?h=metadata>

Questions and comments are most welcome.

I have used IMX219 as an example on routing in a sensor driver in this
version. I also hope I can add OV2740 support in the next version after
testing the patches.

[1] <URL:https://lore.kernel.org/linux-media/20220831141357.1396081-20-tomi.valkeinen@ideasonboard.com/>

since v3:

- Separate preparation patches from this set.

- Add a definition for "Data unit", a pixel that is not image data and use
  it instead in format documentation.

- Fix more numbered lists in dev-subdev.rst.

- Remove a redundant definition for V4L2_META_FMT_GENERIC_CSI2_2_24 ---
  V4L2_META_FMT_GENERIC_CSI2_12 can be used instead.

- Use "X" instead of "p" to denote padding in format documentation.

- Use IMX219 in examples instead of CCS.

- Document that the generic V4L2 CSI-2 metadata formats use padding
  defined in CSI-2 spec and packing defined in CCS spec.

- Add patches to align [GS]_ROUTING behaviour with V4L2. This means mainly
  returning configured routes as part of S_ROUTING as well. "len_routes"
  field is added to denote the length of the array and having more routes
  than fits in the array is no longer an error. Also added more reserved
  fields.

- Added trivial support for S_ROUTING (via G_ROUTING implementation) for
  use in drivers with static-only routes.

- Added helper functions to obtain mbus format as well as crop and compose
  rectangles that are streams-independent.

- Added a patch to define generic CSI-2 long packet types.

- Removed MEDIA_BUS_FMT_IS_META() macro. It didn't seem useful in the end.

- Use a single CCS embedded data format. The bit depth can be selected
  using the meta stream on the source pad.

- Fix mbus code numbers (there were holes due to removed redundant
  formats).

- Fix generic mbus code documentation (byte was being used instead of
  bit).

- Fix spelling of "length".

- Added a patch to remove v4l2_subdev_enable_streams_api that disables
  streams API. This should be merged once libcamera support for streams
  works nicely.

- Don't use strings in printing frame descriptor flags.

- Warn on string truncation in printing frame descriptor.

since v2:

- Add a better example, with formats.

- Add CCS static data media bus codes.

- Added an example demonstrating the use of internal pads. --- Is the
  level of detail enough for the purpose?

- Improved documentation.

- Added a macro to tell whether a format is a metadata format.
  (Documentation could be added.)

- A small ReST syntax fix in the same section.

- Drop leftovers of a patch checking for the INTERNAL_SOURCE flag.

since v1:

- Make the new pad flag just "INTERNAL", requiring either SINK or SOURCE
  pad flag to accompany it. Removed the union in struct v4l2_subdev_route.

- Add the term "stream" to MC glossary.

- Improved and fixed documentation (according to comments).

- Note these formats are little endian.

- Remove 1X8 from the names of the mbus codes. These formats have generally
  8 bits per pixel.

- Fix mbus code numbering (had holes in RFC).

- Add new metadata fields to debug prints.

- Fix a minor documentation build issue.

Sakari Ailus (23):
  media: mc: Add INTERNAL pad flag
  media: uapi: Add generic serial metadata mbus formats
  media: uapi: Document which mbus format fields are valid for metadata
  media: uapi: Add generic 8-bit metadata format definitions
  media: v4l: Support line-based metadata capture
  media: uapi: ccs: Add media bus code for MIPI CCS embedded data
  media: Documentation: ccs: Document routing
  media: Documentation: Additional streams generally don't harm capture
  media: Documentation: Document embedded data guidelines for camera
    sensors
  media: Documentation: v4l: Document source routes
  media: Documentation: Document S_ROUTING behaviour
  media: v4l: subdev: Add helpers for format, crop and compose pointers
  media: ccs: Move ccs_validate_csi_data_format up
  media: ccs: Support frame descriptors
  media: ccs: Add support for embedded data stream
  media: Add MIPI CSI-2 generic long packet type definition
  media: v4l: subdev: Move G_ROUTING handling below S_ROUTING
  media: v4l: subdev: Copy argument back to user also for S_ROUTING
  media: v4l: subdev: Add len_routes field to struct v4l2_subdev_routing
  media: v4l: subdev: Return routes set using S_ROUTING
  media: uapi: Allow a larger number of routes than there's room for
  media: v4l: subdev: Add trivial set_routing support
  media: uapi: v4l: subdev: Enable streams API

 .../driver-api/media/camera-sensor.rst        |  23 +
 .../userspace-api/media/drivers/ccs.rst       |  34 +-
 .../userspace-api/media/glossary.rst          |  14 +
 .../media/mediactl/media-types.rst            |   6 +
 .../userspace-api/media/v4l/dev-meta.rst      |  15 +
 .../userspace-api/media/v4l/dev-subdev.rst    | 208 ++++++++-
 .../userspace-api/media/v4l/meta-formats.rst  |   1 +
 .../media/v4l/metafmt-generic.rst             | 304 +++++++++++++
 .../media/v4l/subdev-formats.rst              | 288 ++++++++++++
 .../media/v4l/vidioc-enum-fmt.rst             |   7 +
 .../media/v4l/vidioc-subdev-g-routing.rst     |  40 +-
 .../media/videodev2.h.rst.exceptions          |   1 +
 drivers/media/i2c/ccs/ccs-core.c              | 419 ++++++++++++++++--
 drivers/media/i2c/ccs/ccs-quirk.h             |   7 +
 drivers/media/i2c/ccs/ccs.h                   |  19 +-
 drivers/media/mc/mc-entity.c                  |  10 +-
 drivers/media/v4l2-core/v4l2-ioctl.c          |  19 +-
 drivers/media/v4l2-core/v4l2-subdev.c         | 132 +++---
 include/media/mipi-csi2.h                     |   1 +
 include/media/v4l2-subdev.h                   |  58 +++
 include/uapi/linux/media-bus-format.h         |  12 +
 include/uapi/linux/media.h                    |   1 +
 include/uapi/linux/v4l2-mediabus.h            |  18 +-
 include/uapi/linux/v4l2-subdev.h              |   8 +-
 include/uapi/linux/videodev2.h                |  18 +
 25 files changed, 1534 insertions(+), 129 deletions(-)
 create mode 100644 Documentation/userspace-api/media/v4l/metafmt-generic.rst


base-commit: 1eb313b9ec4b45825601f4dbf9bd7b441e96f9cc