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Airlie Is Looking At Tournier's Soft FP64 Work For R600-Rats

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  • Airlie Is Looking At Tournier's Soft FP64 Work For R600-Rats

    Phoronix: Airlie Is Looking At Tournier's Soft FP64 Work For R600-Rats

    A few days ago I wrote about David Airlie's work on a new "r600-rats" branch where he's working on bringing up OpenGL 4.2 support to more Radeon HD 5000/6000 series hardware on R600g that's currently limited to OpenGL 3.3. Some questions arose about the FP64 support...

    http://www.phoronix.com/scan.php?pag...Rats-Soft-FP64

  • #2
    Cool, so that was the reason why r600 was limited to 3.3, so the hardware itself does not have proper GL support.

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    • #3
      Originally posted by leipero View Post
      Cool, so that was the reason why r600 was limited to 3.3, so the hardware itself does not have proper GL support.
      More like the hardware is designed to be using soft float in official drivers, as it is too weak to be used for serious fp64 code anyway. No reason to add parts that will never be used.

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      • #4
        Originally posted by leipero View Post
        Cool, so that was the reason why r600 was limited to 3.3, so the hardware itself does not have proper GL support.
        Not all r600, not all... Radeon HD 5800-5900 support hardware fp64, same with Radeon HD 6900. All below series like Radeon hd 5400-5700 and Radeon hd 6400-6800 not support hardware fp64 but in old catalyst driver (fglrx) they use software fp64.

        Also card with hw fp64 can reach OpenGL 4.5 - same like on fglrx if anyone can backport code from other implementation.

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        • #5
          Originally posted by leipero View Post
          Cool, so that was the reason why r600 was limited to 3.3, so the hardware itself does not have proper GL support.
          True, although it's actually more the opposite.

          r600 hardware was out before the GL4 spec was created, so it's GL that didn't properly spec itself to the hardware available at the time.

          It was always stupid to require fp64 for GL 4.0, given that no one really needed or even wanted the feature, and there was hardware out without it. But no one worried about it too much at the time, because NVidia hardware had support, AMD binary drivers already papered around it, and Intel/Mesa were nowhere close to having 4.0 support anyway, so it must have seemed unimportant at the time.

          I believe it was likely brought in to 4.0 mostly for OpenCL interop purposes. In my opinion, GL 4.3 with it's compute shaders would have been a better point to do that.
          Last edited by smitty3268; 05-27-2017, 01:43 PM.

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          • #6
            Originally posted by leipero View Post
            Cool, so that was the reason why r600 was limited to 3.3, so the hardware itself does not have proper GL support.
            It has OpenGL 4.5 support with the old Fglrx and the Windows drivers.

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            • #7
              Rallos Zek Yeah, but what others explained and one post above yours, it's "semi-support" for mid-low end GPU's in 5-6400-6700 series.

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              • #8
                Nice, I thought this had already been abandoned...

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