[Mesa-dev] GBM backend dynamic dispatch method

[Nicolai Hähnle]

On 13.05.2016 00:22, Jammy Zhou wrote:
>
>
> 2016-05-13 12:39 GMT+08:00 Nicolai Hähnle <nhaehnle at gmail.com
> <mailto:nhaehnle at gmail.com>>:
>
>     On 12.05.2016 20:20, Jammy Zhou wrote:
>
>
>
>         2016-05-12 17:39 GMT+08:00 Michel Dänzer <michel at daenzer.net
>         <mailto:michel at daenzer.net>
>         <mailto:michel at daenzer.net <mailto:michel at daenzer.net>>>:
>
>              On 12.05.2016 17:58, Yu, Qiang wrote:
>              > Oh, what a crazy idea. So you mean it can work like this?
>              >
>              > 1. use the libgbm/gbm_dri/libEGL/libGLES from mesa which
>         will load
>              > radeonsi_dri.so
>              >
>              > 2. libGL/amdgpu_dri.so from amdgpu-pro
>
>              glamor uses libEGL/GBM and libGL, so this could only work
>         with Mesa's
>              libGL (or the GLVND one in the future). Can amdgpu_dri.so
>         work with
>              Mesa's libGL right now?
>
>
>         I think amdgpu_dri.so is not completely compatible with Mesa's libGL
>         (considering some special feature requirements for amdgpu-pro
>         and Mesa's
>         evolving). Another problem is that Mesa's libgbm cannot share
>         necessary
>         buffer attributes (such as tiling info, etc) with amdgpu_dri.so
>         at this
>         moment.
>
>
>     I think the long-term plan for such attributes is passing them via
>     amdgpu_bo_metadata (which is defined in libdrm's amdgpu.h). This
>     metadata is read and written directly through libdrm_amdgpu, and so
>     libgbm doesn't have to be involved as far as I can see.
>
>
> Yes, amdgpu_bo_metadata is exactly one good place for such kind of
> information. But IMHO there are still several things to take care. Did I
> miss something?
> - Same meta data definition ("umd_metadata" field) should be used by
> radeonsi and amdgpu-pro.

I absolutely agree that we need to coordinate on how the metadata fields 
are used.

At this time, radeonsi uses and sets the explicit members of 
amdgpu_bo_metadata, i.e. tiling_info and size_metadata. As far as I can 
see, no flags have been defined - flags and umd_metadata are preserved 
by radeonsi if a different UMD were to set them, and are otherwise 
initialized to 0.


> - We need some way to translate gbm_bo or EGLImage into amdgpu_bo, so
> that libdrm_amdgpu interfaces can be used.

In general, how to do this kind of mapping depends on the situation. For 
example, for gbm_bo it is the GBM backend that allocates the gbm_bo 
structure, so C-style inheritance can be used. For example, the DRI 
backend has a type:

struct gbm_dri_bo {
    struct gbm_drm_bo base;

    __DRIimage *image;

    /* Used for cursors and the swrast front BO */
    uint32_t handle, size;
    void *map;
};

It will allocate a struct gbm_dri_bo, and pass a pointer to base back to 
the caller. Then, callbacks implemented by the backend cast the provided 
gbm_bo pointer to gbm_dri_bo. The GBM backend implementation in 
amdgpu-pro can use the same trick, and store whatever internal info it 
requires in the "derived" structure, e.g. an amdgpu_bo_handle.

Cheers,
Nicolai

>
> Regards,
> Jammy
>
>
>     Or is there some use-case that I'm forgetting where libgbm _does_
>     need those attributes?
>
>     Cheers,
>     Nicolai
>
>
>
>              Also, I'm afraid there might still be cases where
>         amdgpu-pro supports
>              new hardware before radeonsi, in which case amdgpu_dri.so
>         needs to
>              support GBM for glamor and EGL in general.
>
>
>         IIRC radeonsi can support Southern Islands and later ASICs. I don't
>         think amdgpu-pro can support pre-GCN products easily, given current
>         amdgpu kernel driver support.
>
>
>
>              Also note that Nvidia developers were talking about
>         possibly creating an
>              nvidia specific GBM backend recently on the wayland-devel
>         mailing list.
>
>
>         Will nvidia open source their code for GBM backend?
>
>
>
>              --
>              Earthling Michel Dänzer               | http://www.amd.com
>              Libre software enthusiast             |             Mesa
>         and X developer
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