Hi Sakari, On Fri, Jun 30, 2023 at 11:43:31PM +0300, Sakari Ailus wrote: > Hi folks, > > Here are a few patches to add support generic, line based metadata as well > as internal source 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. I've just realized that, unless I'm mistaken, we've never documented which of the v4l2_mbus_framefmt fields are valid for metadata formats. Should this be fixed as part of this series ? > 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/20230505205416.55002-1-sakari.ailus@xxxxxxxxxxxxxxx/T/#t> > > I've also pushed these here and I'll keep updating the branch: > > <URL:https://git.linuxtv.org/sailus/media_tree.git/log/?h=metadata> > > Questions and comments are most welcome. > > Driver support is to be added, as well as an example. Jacopo and I are working on this, including libcamera support. > [1] <URL:https://lore.kernel.org/linux-media/20220831141357.1396081-20-tomi.valkeinen@xxxxxxxxxxxxxxxx/> > > 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 (7): > media: mc: Check pad flag validity > media: mc: Add INTERNAL pad flag > media: v4l: subdev: Support INTERNAL pads in routing IOCTLs > media: uapi: v4l: Document source routes > media: uapi: Add generic serial metadata mbus formats > media: uapi: Add generic 8-bit metadata format definitions > media: v4l: Support line-based metadata capture > > .../userspace-api/media/glossary.rst | 6 + > .../media/mediactl/media-types.rst | 6 + > .../userspace-api/media/v4l/dev-meta.rst | 15 + > .../userspace-api/media/v4l/dev-subdev.rst | 20 ++ > .../userspace-api/media/v4l/meta-formats.rst | 1 + > .../media/v4l/metafmt-generic.rst | 331 ++++++++++++++++++ > .../media/v4l/subdev-formats.rst | 257 ++++++++++++++ > .../media/v4l/vidioc-enum-fmt.rst | 7 + > .../media/videodev2.h.rst.exceptions | 1 + > drivers/media/mc/mc-entity.c | 17 +- > drivers/media/v4l2-core/v4l2-ioctl.c | 13 +- > drivers/media/v4l2-core/v4l2-subdev.c | 3 +- > include/uapi/linux/media-bus-format.h | 9 + > include/uapi/linux/media.h | 1 + > include/uapi/linux/videodev2.h | 19 + > 15 files changed, 701 insertions(+), 5 deletions(-) > create mode 100644 Documentation/userspace-api/media/v4l/metafmt-generic.rst -- Regards, Laurent Pinchart
