Hi Hans, On Tue, Aug 08, 2023 at 09:42:07AM +0200, Hans Verkuil wrote: > On 02/08/2023 23:45, Sakari Ailus wrote: > > 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/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. > > > > [1] <URL:https://lore.kernel.org/linux-media/20220831141357.1396081-20-tomi.valkeinen@xxxxxxxxxxxxxxxx/> > > > > since v2: > > > > - 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 (9): > > media: Documentation: Align numbered list > > media: mc: Check pad flag validity > > media: mc: Add INTERNAL pad flag > > media: uapi: v4l: Document source routes > > media: uapi: Add generic serial metadata mbus formats > > media: uapi: Document which mbus format fields are valid for metadata > > media: uapi: Add a macro to tell whether an mbus code is metadata > > media: uapi: Add generic 8-bit metadata format definitions > > media: v4l: Support line-based metadata capture > > FYI: building the documentation results in these warnings: > > Documentation/media/userspace-api/glossary.rst:117: WARNING: term not in glossary: 'V4L2 API' > Documentation/media/userspace-api/glossary.rst:130: WARNING: term not in glossary: 'V4L2 Hardware' > Documentation/media/userspace-api/glossary.rst:194: WARNING: term not in glossary: 'V4L2 API' > Documentation/media/userspace-api/glossary.rst:207: WARNING: term not in glossary: 'V4L2 API' > Documentation/media/userspace-api/glossary.rst:207: WARNING: term not in glossary: 'V4L2 Sub-device' I've seen them, too. I'll post fixes some time soon... -- Sakari Ailus
