[Mesa-dev] Removing GRALLOC_MODULE_PERFORM_GET_DRM_FD

[Stefan Schake]

Hey Robert,

On Wed, Mar 21, 2018 at 4:16 PM, Robert Foss <robert.foss at collabora.com> wrote:
> Hey,
>
> I've started looking into removing the gralloc method
> GRALLOC_MODULE_PERFORM_GET_DRM_FD.
>
> The issues around this seems to be two parts:
> 1) Finding the right device to open
> 2) Sharing the device between components
>
> Sharing the device between components
> -------------------------------------
>
> Currently the device is used by drm_hwc, gbm_gralloc and mesa.
>
> drm_hwc opens the *primary* node in DrmResources::Init() and creates an
> internal model of what properties/components the device has.
>
> gbm_gralloc uses the *render* node during in gbm_dev_create().
>
> Mesa uses uses the *render* node during dri_screen creation in
> dri2_create_screen() and for loading the driver in
> dri2_initialize_android().
>
> However, problematically, drm_hwc uses OpenGL composition as a fallback
> method, and when doing so mesa has to be able to import buffers, which means
> mesa has to use a *primary* node.
>
> The way this is currently worked around in production systems seems to be to
> disable drm master authentication. This is at least what ChromeOS & Intel
> are doing as far as I understand it.
>

Thanks for kicking this off.

I've done a few tests on 2) with VC4 and 8.1.0_r18. With drm_hwc the primary
or master on card0 and gbm_gralloc & Mesa each getting their own fd from
render128, I didn't need any of the DRM authentication hacks in the kernel
anymore. That's with full overlay composition, everything forced to hwui GL
composition or everything done through my hacked up ES2 version of glworker
in drm_hwc (well it made it to launcher until succumbing to a resource leak).
So I don't think mesa would need a master node and could make do with render.

The one thing that mesa on a render node definitely breaks is flink/GEM names
which drm_gralloc uses (the Android-x86 version anyway). No flink anything
with render nodes; drm_gralloc would have to move to dmabuf fds.

That said, it would finally get rid of the strict coupling between Mesa and
gralloc. Ripping out the PERFORM and drm_gralloc facsimile in gbm_gralloc
saves a big bunch of code:

https://github.com/stschake/gbm_gralloc/tree/libdrm_handle_def

With more in mesa/platform_android from the flink stuff.

Thanks,
Stefan