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ATI R600g Gains Mip-Map, Face Culling Support

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  • #31
    Originally posted by rohcQaH View Post
    you're making the assumption that fglrx is neatly modularized with clean inter-module APIs. I wouldn't count on that.
    Not necessarily: they could just rip the offending parts out even if intermingled with the rest, and keep both a "public" and a "private" development branch. With tools like git, this is quite manageable.
    Private code could be marked with a special comment and tools can then prevent accidental release of private code.

    Then there's the legal review. If you follow the news, you'll know how much work legal review is for the OS drivers that are mostly written from a known amount of documentation. Try to imagine sifting through a few hundred thousand lines of fglrx code to determine if it contains any licensed code that mustn't be shared, uses any patents that aren't covered outside of fglrx or tells internals about the hardware which AMD wants to keep secret.

    When AMD/ATI's linux strategy was formed, opening up parts of fglrx was discussed. But it was deemed easier to start from the scratch.
    The result may not be as fast as fglrx, but it's cleaner, better structured code. To me, that's more important.
    I think it should take much less time to review code than to rewrite it from scratch, obviously, especially for very non-trivial parts like how to maximize utilization of the r600+ VLIW ALUs.

    Not to mention that the result is guaranteed to work well and be as good as the original one (if only non-essential parts are withheld), while starting from scratch gives no guarantee of matching fglrx performance at all.

    But the really important thing is that the open source Linux driver would be at least partially a subset of the "real" driver that AMD really cares about, and thus would be guaranteed to be top notch and support new hardware immediately.

    As long as the open driver is separate from the primary driver, hardware will always be supported months late (e.g. no HD 5xxx 3D support almost a year after release!), and the driver won't be competitive for 3D gaming, which is definitely not a desirable outcome for users, and arguably not desirable for AMD either (unless other concerns are more important).

    Obviously, the ATI situation is still much better than the nVidia one, but it still falls way short of the ideal outcome (a top-notch open driver with full AMD software engineering support).

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    • #32
      ATI is never going to open source fglrx, you can forget about that. Despite the few devs they've allocated to the open source drivers, they're still very much a closed source company.

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      • #33
        I can live with full docs and a decent open source driver which can use all the card's features. It doesn't have to be a speed demon either, as long as it's reasonable (i.e. not 20% of the fglrx performance, but more like 75-80%)

        I'd like UVD support, but I can live with shader decoding.

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        • #34
          Originally posted by V!NCENT View Post
          @Agdr,
          you are two things:
          1. license to playback bluray means entire device must be drm'ed
          If they are allowed to release 3D documentation, almost surely they can also release an open driver that only uses that functionality, so I don't think this should be an issue, except for video-related parts that they can just not open at first.

          Obviously there may be DRM-related hooks in the 3D code, but they can be just ripped out and kept in a branch.

          Originally posted by V!NCENT View Post
          @Agdr,
          2. competition is clearly at the driver level and not so much on the hardware, although the theoretical computation power needs to be closely leveled.
          Actually, according for instance to Anandtech's "The RV770 Story: Documenting ATI's Road to Success", hardware seems the deciding factor, particularly the ability to effectively adapt to evolving silicon manufacturing processes (which makes sense, since that's where erformance ultimately comes from).

          Originally posted by V!NCENT View Post
          That said: if AMD releases portions of the driver then they literaly give away their optimisations that can show nVidia their way to victory.
          Yes, this is may be a good argument against opening parts of the driver.
          However, it is likely not the case at least for parts of the driver since they could either be too specific for ATI hardware, already publicly known, already implemented by nVidia or just easy to reverse engineer.

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          • #35
            Agdr, people at AMD have considered this option and decided against it. Trust their judgment. They know more about GPUs than you do. They also know more about their markets and the things they must do to stay in business.

            Your GIT idea doesn't work, either. GIT can do quite a few nice things, but it doesn't magically provide a stable API where there's none. If the branches differ too much, you'll end up with patches that don't apply to both branches, leading to even bigger differences etc.. it can be made to work, but that puts additional requirements on anyone working on that code.
            Remember, their windows drivers are mission-critical. Their linux drivers are not. Allowing the latter to impede work on the former doesn't sound smart to me.

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            • #36
              Actually, the x86 machine code has remained rather stable over the last 20 years. GPUs have a much shorter lifespan and there is more change.

              On the other hand, Gallium3d should be able to help, at least with keeping the generic knowledge in one place. Also, it seems like the major 3d hardware is becoming more similar and doesn't make such radical changes in design as often nowadays.

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              • #37
                Originally posted by rohcQaH View Post
                Remember, their windows drivers are mission-critical. Their linux drivers are not. Allowing the latter to impede work on the former doesn't sound smart to me.
                That doesn't need to be the case.

                They could do development on their proprietary branch as usual and from time to time cherry-pick the commits that can be made public (editing them if necessary) to the public branch (this would be done by the open/linux team). This has no impact at all on windows/proprietary driver development.

                In the worst case, the open driver may lag a bit behind if significant adaptation work has to be done, but that would likely still be much better than the current situation.

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                • #38
                  @Agdr,
                  Do you have any idea about just how much these driver _stacks_ differ?

                  There is no need for code sharing because the know-how is already there and the 'two' drivers differ so much that any code effort of sharing could be spend coding the triple amount of usefulness.

                  Besides, the new floss driver architecture is made to share code with all cards. Intel and nVidia included. So there is no point in sharing with just fglrx for very card specific details.

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                  • #39
                    Like Vincent said, it's not just a "driver", as a separate piece of code.

                    The open source drivers are distributed between the kernel (drm), the X driver and Mesa (which does OpenGL). Now all drivers are migrating over to the Gallium3d infrastructure.

                    Fglrx and the Nvidia blob do all of this inside the kernel blob, and they duplicate much of the code that sits in the X server and the linux kernel as a result.

                    Either you port fglrx to match the open stack (which is a lot of work), or you carefully separate out the parts that can be released into a separate branch, and then develop it with no community help whatsoever and maintain the whole thing on your own. Neither is a good proposition.

                    The most reasonable thing to do is to do the open drivers the Linux way -- by building on the OSS technology like Gallium3d and the kernel drm infrastructure, KMS, etc. This makes the fglrx code difficult to port directly, and the effort it would take is probably no less than writing the thing from scratch.

                    The important thing is opening the docs and providing the basic infrastructure and getting the community involved. I think that AMD are doing it the right way. The problem that few people in the community have both the know-how and the time to contribute is a real one, but a different issue altogether.

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                    • #40
                      Originally posted by V!NCENT View Post
                      @Agdr,
                      Do you have any idea about just how much these driver _stacks_ differ?

                      There is no need for code sharing because the know-how is already there and the 'two' drivers differ so much that any code effort of sharing could be spend coding the triple amount of usefulness.
                      If fglrx/Catalyst were to be opened, it could be used as a full standalone OpenGL stack, without using Mesa and DRM.

                      Alternatively, it could be turned into a Gallium driver: the Gallium driver interface is very similar to the Direct3D 10/11 one, so it should be relatively feasible to convert the Catalyst Direct3D 10/11 driver to become a Gallium driver. The kernel interface would need to be replaced with libdrm-radeon.

                      A third option would be to just integrate the VLIW shader optimizer into r600g. I'd say this is likely the most interesting (i.e. hard to rewrite well, and most self-contained) part of fglrx, and the one easiest to actually reuse in a Mesa/Gallium driver. It is also very AMD-specific, so it shouldn't provide a competitive advantage.

                      Even in this case, the generic parts of the 3D driver could be rather useful to have available when writing equivalent functionality for r600g, especially for advanced stuff like Evergreen tessellation support that the Mesa classic driver probably won't get soon.

                      The source code of their OpenGL 4 implementation, while probably not directly usable in Mesa, could still be insightful and speed up work on GL3 and GL4 for Mesa. nVidia already has their own, so it might be possible to open (unless deeply intertwined with 3rd-party licensed code).

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