On Sat, Nov 25, 2017 at 1:20 PM, Rob Clark <[email protected]> wrote:
> On Sat, Nov 25, 2017 at 12:46 PM, Jason Ekstrand <[email protected]> > wrote: > > On November 24, 2017 09:29:43 Rob Clark <[email protected]> wrote: > >> > >> > >> On Mon, Nov 20, 2017 at 8:11 PM, James Jones <[email protected]> > wrote: > >>> > >>> As many here know at this point, I've been working on solving issues > >>> related > >>> to DMA-capable memory allocation for various devices for some time now. > >>> I'd > >>> like to take this opportunity to apologize for the way I handled the > EGL > >>> stream proposals. I understand now that the development process > followed > >>> there was unacceptable to the community and likely offended many great > >>> engineers. > >>> > >>> Moving forward, I attempted to reboot talks in a more constructive > manner > >>> with the generic allocator library proposals & discussion forum at XDC > >>> 2016. > >>> Some great design ideas came out of that, and I've since been > prototyping > >>> some code to prove them out before bringing them back as official > >>> proposals. > >>> Again, I understand some people are growing concerned that I've been > >>> doing > >>> this off on the side in a github project that has primarily NVIDIA > >>> contributors. My goal was only to avoid wasting everyone's time with > >>> unproven ideas. The intent was never to dump the prototype code as-is > on > >>> the community and presume acceptance. It's just a public research > >>> project. > >>> > >>> Now the prototyping is nearing completion, and I'd like to renew > >>> discussion > >>> on whether and how the new mechanisms can be integrated with the Linux > >>> graphics stack. > >>> > >>> I'd be interested to know if more work is needed to demonstrate the > >>> usefulness of the new mechanisms, or whether people think they have > value > >>> at > >>> this point. > >>> > >>> After talking with people on the hallway track at XDC this year, I've > >>> heard > >>> several proposals for incorporating the new mechanisms: > >>> > >>> -Include ideas from the generic allocator design into GBM. This could > >>> take > >>> the form of designing a "GBM 2.0" API, or incrementally adding to the > >>> existing GBM API. > >>> > >>> -Develop a library to replace GBM. The allocator prototype code could > be > >>> massaged into something production worthy to jump start this process. > >>> > >>> -Develop a library that sits beside or on top of GBM, using GBM for > >>> low-level graphics buffer allocation, while supporting non-graphics > >>> kernel > >>> APIs directly. The additional cross-device negotiation and sorting of > >>> capabilities would be handled in this slightly higher-level API before > >>> handing off to GBM and other APIs for actual allocation somehow. > >> > >> > >> tbh, I kinda see GBM and $new_thing sitting side by side.. GBM is > >> still the "winsys" for running on "bare metal" (ie. kms). And we > >> don't want to saddle $new_thing with aspects of that, but rather have > >> it focus on being the thing that in multiple-"device"[1] scenarious > >> figures out what sort of buffer can be allocated by who for sharing. > >> Ie $new_thing should really not care about winsys level things like > >> cursors or surfaces.. only buffers. > >> > >> The mesa implementation of $new_thing could sit on top of GBM, > >> although it could also just sit on top of the same internal APIs that > >> GBM sits on top of. That is an implementation detail. It could be > >> that GBM grows an API to return an instance of $new_thing for > >> use-cases that involve sharing a buffer with the GPU. Or perhaps that > >> is exposed via some sort of EGL extension. (We probably also need a > >> way to get an instance from libdrm (?) for display-only KMS drivers, > >> to cover cases like etnaviv sharing a buffer with a separate display > >> driver.) > >> > >> [1] where "devices" could be multiple GPUs or multiple APIs for one or > >> more GPUs, but also includes non-GPU devices like camera, video > >> decoder, "image processor" (which may or may not be part of camera), > >> etc, etc > > > > > > I'm not quite some sure what I think about this. I think I would like to > > see $new_thing at least replace the guts of GBM. Whether GBM becomes a > > wrapper around $new_thing or $new_thing implements the GBM API, I'm not > > sure. What I don't think I want is to see GBM development continuing on > > it's own so we have two competing solutions. > > I don't really view them as competing.. there is *some* overlap, ie. > allocating a buffer.. but even if you are using GBM w/out $new_thing > you could allocate a buffer externally and import it. I don't see > $new_thing as that much different from GBM PoV. > > But things like surfaces (aka swap chains) seem a bit out of place > when you are thinking about implementing $new_thing for non-gpu > devices. Plus EGL<->GBM tie-ins that seem out of place when talking > about a (for ex.) camera. I kinda don't want to throw out the baby > with the bathwater here. > Agreed. GBM is very EGLish and we don't want the new allocator to be that. > *maybe* GBM could be partially implemented on top of $new_thing. I > don't quite see how that would work. Possibly we could deprecate > parts of GBM that are no longer needed? idk.. Either way, I fully > expect that GBM and mesa's implementation of $new_thing could perhaps > sit on to of some of the same set of internal APIs. The public > interface can be decoupled from the internal implementation. > Maybe I should restate things a bit. My real point was that modifiers + $new_thing + Kernel blob should be a complete and more powerful replacement for GBM. I don't know that we really can implement GBM on top of it because GBM has lots of wishy-washy concepts such as "cursor plane" which may not map well at least not without querying the kernel about specifc display planes. In particular, I don't want someone to feel like they need to use $new_thing and GBM at the same time or together. Ideally, I'd like them to never do that unless we decide gbm_bo is a useful abstraction for $new_thing. > > I *think* I like the idea of having $new_thing implement GBM as a > deprecated > > legacy API. Whether that means we start by pulling GBM out into it's own > > project or we start over, I don't know. My feeling is that the current > > dri_interface is *not* what we want which is why starting with GBM makes > me > > nervous. > > /me expects if we pull GBM out of mesa, the interface between GBM and > mesa (or other GL drivers) is 'struct gbm_device'.. so "GBM the > project" is just a thin shim plus some 'struct gbm_device' versioning. > > BR, > -R > > > I need to go read through your code before I can provide a stronger or > more > > nuanced opinion. That's not going to happen before the end of the year. > > > >>> -I have also heard some general comments that regardless of the > >>> relationship > >>> between GBM and the new allocator mechanisms, it might be time to move > >>> GBM > >>> out of Mesa so it can be developed as a stand-alone project. I'd be > >>> interested what others think about that, as it would be something worth > >>> coordinating with any other new development based on or inside of GBM. > >> > >> > >> +1 > >> > >> We already have at least a couple different non-mesa implementations > >> of GBM (which afaict tend to lag behind mesa's GBM and cause > >> headaches). > >> > >> The extracted part probably isn't much more than a header and shim. > >> But probably does need to grow some versioning for the backend to know > >> if, for example, gbm->bo_map() is supported.. at least it could > >> provide stubs that return an error, rather than having link-time fail > >> if building something w/ $vendor's old gbm implementation. > >> > >>> And of course I'm open to any other ideas for integration. Beyond just > >>> where this code would live, there is much to debate about the > mechanisms > >>> themselves and all the implementation details. I was just hoping to > kick > >>> things off with something high level to start. > >> > >> > >> My $0.02, is that the place where devel happens and place to go for > >> releases could be different. Either way, I would like to see git tree > >> for tagged release versions live on fd.o and use the common release > >> process[2] for generating/uploading release tarballs that distros can > >> use. > > > > > > Agreed. I think fd.o is the right place for such a project to live. We > can > > have mirrors on GitHub and other places but fd.o is where Linux graphics > > stack development currently happens. > > > >> [2] https://cgit.freedesktop.org/xorg/util/modular/tree/release.sh > >> > >>> For reference, the code Miguel and I have been developing for the > >>> prototype > >>> is here: > >>> > >>> https://github.com/cubanismo/allocator > >>> > >>> And we've posted a port of kmscube that uses the new interfaces as a > >>> demonstration here: > >>> > >>> https://github.com/cubanismo/kmscube > >>> > >>> There are still some proposed mechanisms (usage transitions mainly) > that > >>> aren't prototyped, but I think it makes sense to start discussing > >>> integration while prototyping continues. > >> > >> > >> btw, I think a nice end goal would be a gralloc implementation using > >> this new API for sharing buffers in various use-cases. That could > >> mean converting gbm-gralloc, or perhaps it means something new. > >> > >> AOSP has support for mesa + upstream kernel for some devices which > >> also have upstream camera and/or video decoder in addition to just > >> GPU.. and this is where you start hitting the limits of a GBM based > >> gralloc. In a lot of way, I view $new_thing as what gralloc *should* > >> have been, but at least it provides a way to implement a generic > >> gralloc. > > > > > > +100 > > > > > >> Maybe that is getting a step ahead, there is a lot we can prototype > >> with kmscube. But gralloc gets us into interesting real-world > >> use-cases that involve more than just GPUs. Possibly this would be > >> something that linaro might be interested in getting involved with? > >> > >> BR, > >> -R > >> > >>> In addition, I'd like to note that NVIDIA is committed to providing > open > >>> source driver implementations of these mechanisms for our hardware, in > >>> addition to support in our proprietary drivers. In other words, > wherever > >>> modifications to the nouveau kernel & userspace drivers are needed to > >>> implement the improved allocator mechanisms, we'll be contributing > >>> patches > >>> if no one beats us to it. > >>> > >>> Thanks in advance for any feedback! > >>> > >>> -James Jones > >>> _______________________________________________ > >>> mesa-dev mailing list > >>> [email protected] > >>> https://lists.freedesktop.org/mailman/listinfo/mesa-dev > >> > >> _______________________________________________ > >> mesa-dev mailing list > >> [email protected] > >> https://lists.freedesktop.org/mailman/listinfo/mesa-dev > > > > > > >
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