Hello, On Fri, Jun 02, 2023 at 08:54:35AM +0100, Naushir Patuck wrote: > Hi Sakari, > > Thank you for working on this. Sensor metadata is something that Raspberry Pi > do make extensive use of, and our downstream changes to support it, although a > bit hacky, are not too dissimilar to your proposal here. > > On Fri, 5 May 2023 at 22:53, 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. > > > > 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. Optical dark pixels are image data, I wouldn't include them in the "metadata" category. They can of course be transmitted over a different stream, so they're relevant to the API being designed. > > 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. Strictly speaking, the number of metadata formats depends on how we define "format". Today, we can use the GREY pixel format to capture greyscale images in the visible spectrum, but also IR images, thermal images, or even depth images. They're all one pixel format. On the other hand, we have Y16 for greyscale visible and IR images, and Z16 for depth maps. It's already a mess, even without metadata :-) > > 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. I'm glad we agree on this. > > 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). Decoupling the information needed by the kernel (e.g. are we transporting RAW8 or RAW10 from the sensor through the pipeline) from the information useful for userspace only (e.g. the sensor embedded data is encoding using register + value pairs, based on the IMX708 registers set) is a good idea. I expect the main question to be where to draw the line between those two categories. Some pieces of information may be useless to any processing block in the pipeline except for an odd block in the middle. This is, I believe, a problem similar to the CFA pattern. That information is useless for most devices, but required by the demosaicing block and some other blocks along the pipeline (colour gains for instance, or some Bayer statistics engines). We currently convey the CFA pattern in the media bus codes and pixel formats (e.g. SGRBG8 vs. SRGGB8) through the whole pipeline, while it could be conveyed out of band (e.g. exposed by the sensor using a control, and set on the devices that need it using a control as well). If we come up with a good solution for metadata (and I hope we will), maybe we'll be able to use a similar mechanism for CFA patterns, simplifying new drivers and userspace. Or maybe this will remain a pipe dream given the backward compatibility implications. > > 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. > > One thing that may be worth considering or clarifying - for the case of the > BCM2835 Unicam CSI-2 device, we only have 2x DMA output channels. So one will > match image data packets, and the other will match "everything else". Typically > "everything else" would only be CSI-2 embedded data, but in the case of the > Raspberry Pi Camera v3 (IMX708), it includes embedded data, PDAF data, and > HDR histogram data. Each of these outputs can be programmed to use a different > packet ID in the sensor, but since Unicam only has a single DMA for "everything > else", it all gets dumped into one metadata buffer. But given we know the exact > structure of the data streams, it's trivial for useland to find the right bits > in this buffer. Of course, other CSI-2 receivers with more DMA channels might > allow these streams to end up in their own buffers. > > Nothing in your series seems to stop us operating Unicam in this way, > particularly because there is no fixed definition of the data format for > V4L2_META_FMT_GENERIC_8. So I don't think it's a problem, but perhaps it's worth > documenting that the metadata might include multiple streams from the sensor? Thanks for your feedback Naush. Would you consider reviewing the individual patches in the series ? :-) > > 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. > > > > > > [1] <URL:https://lore.kernel.org/linux-media/20220831141357.1396081-20-tomi.valkeinen@xxxxxxxxxxxxxxxx/> > > > > Sakari Ailus (7): > > media: mc: Add INTERNAL_SOURCE pad type flag > > media: v4l: subdev: Support INTERNAL_SOURCE pads in routing IOCTLs > > media: uapi: v4l: Document source routes > > media: mc: Check pad flag validity > > media: uapi: Add generic serial metadata mbus formats > > media: uapi: Add generic 8-bit metadata format definitions > > media: v4l: Support line-based metadata capture > > > > .../media/mediactl/media-types.rst | 7 + > > .../userspace-api/media/v4l/dev-meta.rst | 15 + > > .../userspace-api/media/v4l/dev-subdev.rst | 18 + > > .../userspace-api/media/v4l/meta-formats.rst | 1 + > > .../media/v4l/metafmt-generic.rst | 317 ++++++++++++++++++ > > .../media/v4l/subdev-formats.rst | 257 ++++++++++++++ > > .../media/v4l/vidioc-enum-fmt.rst | 7 + > > .../media/v4l/vidioc-subdev-g-routing.rst | 5 + > > drivers/media/mc/mc-entity.c | 20 +- > > drivers/media/v4l2-core/v4l2-ioctl.c | 8 + > > drivers/media/v4l2-core/v4l2-subdev.c | 6 +- > > include/uapi/linux/media-bus-format.h | 9 + > > include/uapi/linux/media.h | 1 + > > include/uapi/linux/v4l2-subdev.h | 6 +- > > include/uapi/linux/videodev2.h | 19 ++ > > 15 files changed, 691 insertions(+), 5 deletions(-) > > create mode 100644 Documentation/userspace-api/media/v4l/metafmt-generic.rst -- Regards, Laurent Pinchart
