Em Wed, 6 Jun 2018 13:19:39 +0900 Tomasz Figa <tf...@chromium.org> escreveu:
> On Mon, Jun 4, 2018 at 10:33 PM Mauro Carvalho Chehab > <mchehab+sams...@kernel.org> wrote: > > > > Hi all, > > > > I consolidated hopefully all comments I receive on the past announcement > > with regards to the complex camera workshop we're planning to happen in > > Tokyo, just before the Open Source Summit in Japan. > > > > The main focus of the workshop is to allow supporting devices with MC-based > > hardware connected to a camera. > > > > I'm enclosing a detailed description of the problem, in order to > > allow the interested parties to be at the same page. > > > > We need to work towards an agenda for the meeting. > > > > From my side, I think we should have at least the following topics at > > the agenda: > > > > - a quick review about what's currently at libv4l2; > > - a presentation about PipeWire solution; > > - a discussion with the requirements for the new solution; > > - a discussion about how we'll address - who will do what. > > I believe Intel's Jian Xu would be able to give us some brief > introduction to IPU3 hardware architecture and possibly also upcoming > hardware generations as well. That would be great! > My experience with existing generations of ISPs from other vendors is > that the main principles of operation are very similar to the model > represented by IPU3 and very much different to the OMAP3 example > mentioned by Mauro below. I further commented on it below. > > > > > Comments? Suggestions? > > > > Are there anyone else planning to either be there physically or via > > Google Hangouts? > > > > Tomaz, > > > > Do you have any limit about the number of people that could join us > > via Google Hangouts? > > > > Technically, Hangouts should be able to work with really huge > multi-party conferences. There is obviously some limitation on client > side, since thumbnails of participants need to be decoded at real > time, so even if the resolution is low, if the client is very slow, > there might be some really bad frame drop happening on client side. > > However, I often have meetings with around 8 parties and it tends to > work fine. We can also disable video of all participants, who don't > need to present anything at the moment and the problem would go away > completely. Ok, good! > > Regards, > > Mauro > > > > --- > > > > 1. Introduction > > =============== > > > > 1.1 V4L2 Kernel aspects > > ----------------------- > > > > The media subsystem supports two types of devices: > > > > - "traditional" media hardware, supported via V4L2 API. On such hardware, > > opening a single device node (usually /dev/video0) is enough to control > > the entire device. We call it as devnode-based devices. > > An application sometimes may need to use multiple video nodes with > > devnode-based drivers to capture multiple streams in parallel > > (when the hardware allows it of course). That's quite common for > > Analog TV devices, where both /dev/video0 and /dev/vbi0 are opened > > at the same time. > > > > - Media-controller based devices. On those devices, there are typically > > several /dev/video? nodes and several /dev/v4l2-subdev? nodes, plus > > a media controller device node (usually /dev/media0). > > We call it as mc-based devices. Controlling the hardware require > > opening the media device (/dev/media0), setup the pipeline and adjust > > the sub-devices via /dev/v4l2-subdev?. Only streaming is controlled > > by /dev/video?. > > > > In other words, both configuration and streaming go through the video > > device node on devnode-based drivers, while video device nodes are used > > used for streaming on mc-based drivers. > > > > With devnode-based drivers, "standard" media applications, including open > > source ones (Camorama, Cheese, Xawtv, Firefox, Chromium, ...) and closed > > source ones (Skype, Chrome, ...) support devnode-based devices[1]. Also, > > when just one media device is connected, the streaming/control device > > is typically /dev/video0. > > > > [1] It should be noticed that closed-source applications tend to have > > various bugs that prevent them from working properly on many devnode-based > > devices. Due to that, some additional blocks were requred at libv4l to > > support some of them. Skype is a good example, as we had to include a > > software scaler in libv4l to make it happy. So in practice not everything > > works smoothly with closed-source applications with devnode-based drivers. > > A few such adjustments were also made on some drivers and/or libv4l, in > > order to fulfill some open-source app requirements. > > > > Support for mc-based devices currently require an specialized application > > in order to prepare the device for its usage (setup pipelines, adjust > > hardware controls, etc). Once pipeline is set, the streaming goes via > > /dev/video?, although usually some /dev/v4l2-subdev? devnodes should also > > be opened, in order to implement algorithms designed to make video quality > > reasonable. > > To further complicate the problem, on many modern imaging subsystems > (Intel IPU3, Rockchip RKISP1), there is more than 1 video output > (CAPTURE device), for example: > 1) full resolution capture stream and > 2) downscaled preview stream. OMAP3 also has both full-res and downscaled for previews, on separate /dev/video. On a "simple" usecase (like PC apps and videoconference), just one /dev/video is enough. For devices used to take static pictures, both streams are important. > Moreover, many ISPs also produce per-frame metadata (statistics) for > 3A algorithms, which then produces per-frame metadata (parameters) for > processing of next frame. These would be also exposed as /dev/video? > nodes with respective V4L2_BUF_TYPE_META_* queues. True, but the metadata frames don't need to go the the application, as it will be consumed by the 3A logic. > > It is complicated even more on systems with separate input (e.g. CSI2) > and processing (ISP) hardware, such as Intel IPU3. In such case, the > raw frames captured from the CSI2 interface directly are not usable > for end-user applications. This means that some component in userspace > needs to forward the raw frames to the ISP and only the output of the > ISP can be passed to the application. Yes. Nowadays, several devices do the same. > > On such devices, it is not uncommon that the device used by the > > application to be a random number (on OMAP3 driver, typically, is either > > /dev/video4 or /dev/video6). > > > > One example of such hardware is at the OMAP3-based hardware: > > > > > > http://www.infradead.org/~mchehab/mc-next-gen/omap3-igepv2-with-tvp5150.png > > > > On the picture, there's a graph with the hardware blocks in blue/dark/blue > > and the corresponding devnode interfaces in yellow. > > > > The mc-based approach was taken when support for Nokia N9/N900 cameras > > was added (with has OMAP3 SoC). It is required because the camera hardware > > on SoC comes with a media processor (ISP), with does a lot more than just > > capturing, allowing complex algorithms to enhance image quality in runtime. > > Those algorithms are known as 3A - an acronym for 3 other acronyms: > > > > - AE (Auto Exposure); > > - AF (Auto Focus); > > - AWB (Auto White Balance). > > > > The main reason that drove the MC design is that the 3A algorithms (that is > > the 3A control loop, and sometimes part of the image processing itself) > > often > > need to run, at least partially, on the CPU. As a kernel-space > > implementation > > wasn't possible, we needed a lower-level UAPI. > > > > Setting a camera with such ISPs are harder because the pipelines to be > > set actually depends the requirements for those 3A algorithms to run. > > Also, usually, the 3A algorithms use some chipset-specific userspace API, > > that exports some image properties, calculated by the ISP, to speed up > > the convergence of those algorithms. > > > > Btw, usually, the 3A algorithms are IP-protected, provided by vendors > > as binary only blobs, although there are a few OSS implementations. > > > > Part of the problem is that, so far, there isn't a proper userspace API > > to implement 3A libraries. Once we have an userspace camera stack, we > > hope that we'll gradually increase the number and quality of open-source > > 3A stacks. > > > [snip] > > > > 2.2 Modern hardware is starting to come with "complex" camera ISP > > ----------------------------------------------------------------- > > > > While mc-based devices were limited to SoC, it was easy to > > "delegate" the task of talking with the hardware to the > > embedded hardware designers. > > > > However, this is changing. Dell Latitude 5285 laptop is a standard > > PC with an i3-core, i5-core or i7-core CPU, with comes with the > > Intel IMU3 ISP hardware[2]. > > IPU3 :) Yeah, I noticed the typo too late. I actually fixed it at the announcement at linuxtv.org. > > > > [2] https://www.spinics.net/lists/linux-usb/msg167478.html > > > > There, instead of an USB camera, the hardware is equipped with a > > MC-based ISP, connected to its camera. Currently, despite having > > a Kernel driver for it, the camera doesn't work with any > > userspace application. > > > > I'm also aware of other projects that are considering the usage of > > mc-based devices for non-dedicated hardware. > > > [snip] > > > > 3.2 libv4l2 support for 3A algorithms > > ===================================== > > > > The 3A algorithm handing is highly dependent on the hardware. The > > idea here is to allow libv4l to have a set of 3A algorithms that > > will be specific to certain mc-based hardware. > > > > One requirement, if we want vendor stacks to use our solution, is that > > it should allow allow external closed-source algorithms to run as well. > > > > The 3A library API must be standardized, to allow the closed-source > > vendor implementation to be replaced by an open-source implementation > > should someone have the time and energy (and qualifications) to write > > one. > > > > Sandboxed execution of the 3A library must be possible as closed-source > > can't always be blindly trusted. This includes the ability to wrap the > > library in a daemon should the platform's multimedia stack wishes > > and to avoid any direct access to the kernel devices by the 3A library > > itself (all accesses should be marshaled by the camera stack). > > > > Please note that this daemon is *not* a camera daemon that would > > communicates with the V4L2 driver through a custom back channel. > > > > The decision to run the 3A library in a sandboxed process or to call > > it directly from the camera stack should be left to the camera stack > > and to the platform integrator, and should not be visible by the 3A > > library. > > > > The 3A library must be usable on major Linux-based camera stacks (the > > Android and Chrome OS camera HALs are certainly important targets, > > more can be added) unmodified, which will allow usage of the vendor > > binary provided for Chrome OS or Android on regular Linux systems. > > This is quite an interesting idea and it would be really useful if it > could be done. I'm kind of worried, though, about Android in > particular, since the execution environment in Android differs > significantly from a regular Linux distributions (including Chrome OS, > which is not so far from such), namely: > - different libc (bionic) and dynamic linker - I guess this could be > solved by static linking? Static link is one possible solution. IMHO, we should try to make it use just a C library (if possible) and be sure that it will also compile with bionic/ulibc in order to make it easier to be used by Android and other embedded distros. > - dedicated toolchains - perhaps not much of a problem if the per-arch > ABI is the same? Depending on library dependency, we could likely make it work with more than one toolchain. I guess acconfig works with Android, right? If so, it could auto-adjust to the different toolchains everywhere. > > It would make sense to design a modular camera stack, and try to make > > most components as platform-independent as possible. This should include: > > > > - the kernel drivers (V4L2-compliant and usable without any closed-source > > userspace component); > > - the 3A library > > - any other component that could be shared (for instance a possible > > request API library). > > > > The rest of the code will mostly be glue around those components to > > integrate them in a particular camera stack, and should be as > > platform-agnostic as possible. > > > > In the case of the Android camera HAL, ideally it would be a glue that > > could be used with different camera vendors (probably with some kind of > > vendor-specific configuration, or possibly with a separate vendor-specific > > component to handle pipeline configuration). > > > > 4 Complex camera workshop > > ========================= > > > > The workshop will be happening in Tokyo, Japan, at Jun, 19, at the > > google offices. The location is: > > > > 〒106-6126 Tokyo, Minato, Roppongi, 6 Chome−10−1 Roppongi Hills Mori Tower > > 44F > > Nearest station exits: > - Hibiya line Roppongi station exit 1c (recommended) > - Oedo line Roppongi station exit 3 (and few minutes walk) > > > > > 4.1 Physical Attendees > > ====================== > > > > Tomasz Figa <tf...@google.com> > > Mauro Carvalho Chehab <Mauro Carvalho Chehab <mchehab+sams...@kernel.org> > > Kieran Bingham <kieran.bing...@ideasonboard.com> > > Laurent Pinchart <laurent.pinch...@ideasonboard.com> > > Niklas Söderlund <niklas.soderl...@ragnatech.se> > > Zheng, Jian Xu Zheng <jian.xu.zh...@intel.com> > > > > Anywone else? > > Looking at latest reply in this thread: > > jacopo mondi <jac...@jmondi.org> > > Anyone else, please tell me beforehand (at least 1-2 days before), as > I need to take care of building access, since it's a multi-tenant > office building. I'll contact each attendee separately with further > details by email. > > > > > 4.2. Attendees Via Google Hangouts > > ================================== > > > > Hans Verkuil <hverk...@xs4all.nl> - Via Google Hangouts - maybe only on > > afternoon > > Javier Martinez Canillas <jav...@dowhile0.org> - Via Google Hangouts - only > > on reasonable TZ-compatible-hours > > What time zone would that be? I guess we could try to tweak the agenda > to take this into account. Thanks, Mauro
